Appendix 1. USDA Notifications and States Approved for Environmental 

Releases of DAS-40278-9 corn, DAS-68416-4 soybean, and 

DAS-44406-6 soybean

Page 1-1
USDA

Notification

Number

Notification

Authorization

Date

Notification

Expiration

Date

State(s)

09-086-105n 4/20/2009 4/20/2010 IL, IN, IA, MN, MO, NE, WI

09-090-107n 4/21/2009 4/21/2010

CA, GA, IL, IA, IN,

KS, MI, MN, MO,

OH, NE, NJ, OK, PA, TX

09-075-106n 3/26/2009 3/26/2010 HI, IA, IL, IN, MN, NE, NE, SD, WI

09-061-005n 4/6/2009 4/6/2010 IA, MN, MS, NY, OH

09-005-107n 1/15/2009 1/15/2010 HI, IL, IN, IA, NE, PR

08-259-103n 10/15/2008 10/15/2009 HI

08-133-107n 6/1/2008 6/1/2009 IL (1), TX (1)

08-021-110n 4/1/2008 4/1/2009 IA

08-021-104n 3/20/2008 3/20/2009

IL (7), IN (11), IA

(6), MN (4), MS (1),

NE (4), WI (3)

07-242-103n 10/15/2007 10/15/2008 HI

06-338-101n 1/29/2007 1/29/2008 HI

05-308-03n 12/13/2005 12/13/2006 HI

Table 1-1. USDA Notifications and States Approved for Environmental Releases of DAS40278-9 corn

Page 1-2
Table 1-2. USDA Notifications and States Approved for Environmental Releases of DAS68416-4 soybean

USDA

Notification

Number

Notification

Authorization

Date

Notification

Expiration

Date State(s)

09-259-105n 9/25/2009 9/25/2010 PR

09-086-101n 5/30/2009 5/30/2010 IL, IN, IA, MN, MO, NE, WI

09-084-110n 4/15/2009 4/15/2010 AL, AR, CA, GA, IL,

IN, IA, MI, MN, MO, MS, NE, OH

09-075-105n 4/15/2009 4/15/2010 HI, IN, IA, PR

09-068-101n 4/13/2009 4/13/2010 AR, IL, IN, IA, MD,

MI, MO, ND, NE, OH, PR, WI

09-061-104n 4/6/2009 4/6/2010 AR, IL, IN, IA, MN, MS, NY, OH, TN

09-005-108n 1/1/2009 1/1/2010 HI

08-323-102n 12/3/2008 12/3/2009 PR

08-254-110n 9/26/2008 9/26/2009 PR

08-170-103n 6/26/2008 6/26/2009 MO

08-137-103n 6/5/2008 6/5/2009 MD

08-121-103n 5/14/2008 5/14/2009 IA

08-121-102n 5/15/2008 5/15/2009 IL, IN, MO, NE, OH

08-071-107n 4/14/2008 4/14/2009 CA, IL, IN, IA, MN, MN, NE

07-242-107n 9/30/2007 9/30/2008 PR

06-292-105n 12/1/2006 12/1/2007 IN

Page 1-3
USDA

Notification

Number

Notification

Authorization

Date

Notification

Expiration

Date

State(s)

11-095-105n 4/29/2011 4/29/2012 MS

11-087-114n 4/20/2011 4/20/2012 AL, AR, GA, IL, IN, MD, NE

11-067-105n 3/30/2011 3/30/2012

AR, CA, IA, IN,

IL, LA, MN,

MO, MS, OH, WI

10-243-104n 9/30/2010 9/30/2011 PR

10-085-103n 4/19/2010 4/19/2011 GA, IA, IN,IL, MI, MO, NE

10-083-105n 4/22/2010 4/22/2011 IA, IN, MO,MS

10-077-107n 4/14/2010 4/14/2011

GA, IA, IN,IL,

MD, MO,NE, OH, PR

09-259-108n 10/5/2009 10/5/2010 PR

09-068-103n 4/1/2009 4/1/2010 IN, PR

08-254-109n 9/30/2008 9/30/2009 PR

Table 1-3. USDA Notifications and States Approved for Environmental Releases of DAS44406-6 soybean

1

Pending reports as of June 21, 2011 to be submitted within six months of the notification

expiration date.

Page 1-4
Appendix 2. Summary of Public Comments

Page 2-1
Public Scoping Comments

Members of the public were invited to participate in the scoping process for this draft EIS through 

an announcement of a Notice of Intent (NOI) to prepare an Environmental Impact Statement (EIS) 

in connection with making a determination on the status of DowAgrosciences (DAS) petitions 09-

233-01p (event DAS-40278-9 corn), 09-349-01p (event DAS-68416-4 soybean), and 11-234-01p 

(event DAS-44406-6 soybean). APHIS published a NOI to prepare an EIS for the three petitions 

and requested public comments for scoping the EIS in the Federal Register on May 16, 2013. The 

60-day public comment period closed on July 17, 2013. The docket file was published 

at http://www.regulations.gov/#!docketDetail;D=APHIS-2013-0042.

In this NOI, APHIS asked for comments, data, and information regarding 18 broad, overlapping 

issues. APHIS also requested the public to provide suggestions for other issues to be discussed or 

alternatives to be analyzed in the draft EIS. During this comment period, APHIS received 41

comments (see summary in Table 2-1) with an additional 9 comments from the virtual public 

meetings (see summary in Table 2-2). Comments were made by interest groups, industry 

representatives, industry trade organizations, growers, private individuals, scientists, agronomists 

and crop specialists, and a Federal agency. Full text of the comments received during the open 

comment period is available online at www.regulations.gov.

In addition to posting written comments directly to the docket, members of the public were given 

opportunities to provide their comments directly to APHIS during public meetings held on June 26 

and 27, 2013. Transcripts of the public meetings are available as follows:

For the June 26, 2013, virtual meeting:

http://www.aphis.usda.gov/biotechnology/downloads/VPM/062613/VPM_062613_transcript.pdf

For June 27, 2013, virtual meeting:

http://www.aphis.usda.gov/biotechnology/downloads/VPM/062713/VPM_062713_transcript.pdf

In all, a total of 50 public comments were received with 41 public comments submitted to the 

docket folder on the NOI for the preparation of an EIS on 2,4-D-resistant corn and soybean and an 

additional 9 comments were given on the NOI during the virtual meetings. 

APHIS used the public comments to identify issues to be considered in development of the Draft 

EIS. A number of commenters indicated they object to APHIS NOI to prepare an EIS, finding the 

level of analysis performed in the EAs scientifically sufficient. These commenters felt preparing 

an EIS unnecessarily keeps valuable traits and tools currently needed by growers battling 

herbicide-resistant weeds. 

Overall, the comments submitted echoed the issues previously raised in the public comments made 

on the petitions and/or draft EAs for the three events. Most of the comments continued to voice 

concern over the potential increased use of 2,4-D by growers with adoption of the three 

deregulated events. While APHIS recognizes these concerns, APHIS does not regulate pesticide 

use. EPA is reviewing and analyzing the information DAS has submitted in support of the 

registration of their new 2,4-D choline salt formulation. This includes assessing the physical and 

Page 2-2
chemical properties of, fate and transport of, and impacts to the environment and human health 

from the new formulation. APHIS has no input into the decision of permitting the use of the new 

2,4-D formulation; therefore, those issues are not analyzed in this EIS. 

The public comments on the NOI, the two draft EAs, and the petitions were grouped into several 

main themes. Below is a summary of the issues identified in the public scoping comments.

1. Alternatives

• Consider an alternative involving mandatory weed resistance management.

• Provide an assessment of Integrated Weed Management (IWM) systems or non- chemical 

tactics as an alternative to deregulation of DAS‐68416-4 soybean for the stated purpose of 

Dow’s product, to provide a means to control glyphosate-resistant weeds

• The statement of purpose and need is missing from the notices. To what need and for 

what purposes are petitioners responding in developing and commercializing their 

products? The answer to this question largely determines the range of reasonable 

alternatives the agency must consider in the NEPA process.

• Granting (with or without conditions) or denying petitions does not constitute 

“alternatives” to be considered in NEPA’s environmental impact statement process; 

rather, they are decision options for the agency (see my earlier comment for 

explanation). Alternatives that must be considered under NEPA relate directly to the 

purposes of and need for proposed actions.

2. Inserted Genes/Plant Composition

• Degree of resistance conferred by the transgene in different plant parts and stages of 

development.

• APHIS did not take into account the potential toxicity of DAS-40278-9 corn, DAS-68416-4 

soybean, and DAS-44406-6 soybean to listed species that might eat leaves, roots, stems, or 

flower parts. Migrating birds, for example, eat parts of the soybean plant. Bees consume 

the pollen and nectar, and presumably other insects do as well. Soybean detritus washes 

into wetlands.

• APHIS should initiate consultations with FWS and NMFS concerning the approval of 

DAS-40278-9 corn, DAS-68416-4 soybean, and DAS-44406-6 soybean.

• Assess the characteristics of DAS-40278-9 corn conferred by the activity of the novel 

enzyme AAD-1 and potential impacts.

• Analyze composition of the AAD-1 protein in the crop after exposure of DAS-40278-9 

corn to 2,4-D or quizalofop.

• Perform additional research and information regarding any impacts to the nutritive value of 

DAS-68416-4 soybean compared to non-GE soybean. The commenter stated that the U.S. 

Food and Drug Administration (FDA) noted several differences in the compositional 

analysis of DAS soybean. Although the FDA recognized DAS-68416-4 Soybean as safe, 

the commenter requested a description of the differences, including supporting data, to 

confirm the DAS soybean is as safe as conventional soybean varieties. The commenter also 

requested additional research beyond the initial 15-day study to determine the safety of the 

Page 2-3
AAD-12 protein to confirm the nutritional differences would not affect human or animal 

health.

• More research must be done to show that these nutritional differences do not result in any 

functional differences that could affect human or animal health when this corn is present in 

food or animal feed.

• Information on the degree of resistance conferred by the transgene in different plant parts 

and stages of development should be available for review by APHIS and the public.

• Information on the expression of the transgene in pollen, nectar, and levels of herbicide 

residues. Metabolites in pollen and nectar should be available for review by APHIS and the 

public. 

3. Miscellaneous

• Prove the deregulation will neither jeopardize any species nor harm any critical habitat 

anywhere the crop system may be grown.

• The conversion of natural areas and Conservation Reserve Program lands to corn 

production and the resultant increase in herbicide use would result in adverse impacts to 

listed threatened and endangered species, because these areas have not been previously 

farmed and are likely to support native species.

• Tillage can greatly reduce selection pressure on herbicides and thus aid in prevention of 

herbicide resistance. Tillage can also aid in management of resistant weeds once they 

become a problem. Tillage, however, is not an option in most cases. Our growers have 

worked hard to make no-till a success on their farms. They adopted no-till partly because of 

conservation compliance requirements in the past several farm bills. But regardless of 

conservation compliance, the major driving force was economics. Savings in fuel, labor, 

and equipment through no-till production helped growers remain competitive. A return to 

tillage would be a step backwards in terms of productivity and environmental protection. 

Moreover, growers simply do not have the labor and equipment to go back to tillage.

• Address the cumulative impact of seed market concentration. The seed market 

concentration impacts of a deregulation of 2,4-D resistant corn constitute a significant 

intertwined socioeconomic impact that is reasonably foreseeable.

• Assess economic impact of the higher cost of 2,4-D resistant corn to farmers.

• APHIS should find or develop studies that explore the extent to which pricing strategies for 

HR crop systems (e.g. high-priced seed, low-cost herbicide) reinforce herbicide use patterns 

that foster resistance in the case of 2,4-D-resistant corn and soybeans. 

• Consider the possible impacts that yet another genetic trait can have on farmers in Mexico 

and around the world where native maize and wild corn relatives are not only grown, but an 

indispensable part of their culture and the economy. 

• Conduct a larger analysis of domestic socioeconomic impacts given that biotech soybeans 

are more costly than non-biotech seeds and would increase costs for farmers.

• Herbicide tolerant crops have made the no-till system much more timely and cost effective 

for our operation. The no-till system is so effective at controlling erosion in our area that if 

we had to go back to tillage to control resistant weeds, the long-term cost would be very 

high in soil loss alone.

• Biotechnology has allowed plant breeders to develop soybeans that are tolerant to 

herbicides, thus allowing soybean farmers to better control weeds and implement no-till 

Page 2-4
and conservation tillage practices that save fuel, reduce erosion, and protect the 

environment.

• APHIS must assess 2,4-D-resistant corn and soybeans as crop systems comprising the 

herbicide-resistant crop itself and associated use of 2,4-D.

• APHIS should examine both short-term and long-term impacts of the proposed herbicideresistant crop systems in the light of what has been learned from real-world experiences 

with previously-approved herbicide-resistant crop systems. What are the likely similarities 

and differences in terms of environmental health and economic concerns?

• APHIS has often claimed that, although individual farmers may be affected by releasing 

genetically engineered organisms in the area, when examined in total, none of the potential 

business losses is expected to be so severe as to amount to a significant impact. This 

determination fails to recognize that environmental “significance” exists at all 

levels―“society as a whole (human, national), the affected region, the affected interests, 

and the locality.” 

• The USDA’s Environmental Impact Statement must include, at a minimum research on 

how the ingestion of foods manufactured from these crops will affect human health and 

how the continued use of the herbicide in agriculture could endanger agricultural workers 

and the general public.

• Thus, 92% of Georgia cotton growers hand-weed 52% of the crop with an average cost of 

$23 per hand-weeded acre, which is an increase of at least 475% as compared to hand 

weeding costs prior to resistance. In addition to increased herbicide use and hand weeding, 

growers in Georgia have indicated that they are using mechanical, in-crop cultivation (44% 

of acres), tillage for the incorporation of pre-plant herbicides (20% of the acres), and deep 

turning (19% of the acres every three years) to aid in Palmer amaranth control. Current 

weed management systems are extremely diverse, complex, less environmentally friendly, 

and costly when compared to those systems employed only a decade ago. Growers are in 

desperate need of new technologies that will aid in the management of glyphosate-resistant 

Palmer amaranth, and other problematic weeds, for long term sustainability.

• The introduction of soybeans tolerant to 2,4-D will allow an additional mode of action to be 

used in the system, allowing for better weed control and harvested soybeans with less 

foreign material from weed seeds, a valuable characteristic for processors.

• APHIS should assess the socioeconomic consequences of 2,4-D-resistant corn and 

soybeans, in terms of increased land and rental prices from increased competition for land, 

increased average size of farms, and accelerated exit of small- to medium-size farmers from 

agriculture.

4. Herbicide-Resistant Weeds

• Provide analysis of the prevalence/emergence of glyphosate‐resistant weeds.

• Weed resistance is a well understood scientific phenomenon that is not unique to 

biotechnology or any other form of agriculture. Different herbicides attack weeds by 

different methods or “modes of action.”

• Overuse of any herbicide technology leads to selection pressure for development of 

resistance to that technology. Resistance to other herbicides was problematic previously 

and thus will continue to present management problems for growers in terms of herbicide 

Page 2-5
alternatives that remain as effective options. New cases of weed resistance will evolve in 

response to current soybean weed management programs. 

• Science has clearly shown that there is a risk of resistance development to all herbicides, 

and 2,4-D and dicamba are no exception. In fact, weeds have evolved resistance to nearly 

all forms of weed control including herbicides, tillage, mowing and hand weeding.

• The greatest risk for developing herbicide resistance is actually occurring right now with 

the PPO herbicides and glufosinate. These products are being over-used in certain cropping 

systems as farmers have no other effective herbicide options. The 2,4-D and dicamba 

resistant crops could be used to delay resistance development to the PPO herbicides and 

glufosinate and, in turn, weed management systems could be developed using the PPO 

herbicides, glufosinate, 2,4-D and dicamba, extending the life of each of these chemistries.

• Growers need multiple modes of action to help manage herbicide-resistant weeds.

• Because of the resistance threat, growers are now more likely than ever to utilize multiple 

weed management strategies (tillage, row spacing, cover crops, residual herbicides, 

mechanical cultivation, and hand-weeding) in combination with herbicide-resistant crops.

• APHIS provides no empirical assessment of farmer use of resistant weed mitigation 

measures at all, but rather flaccidly relies on Dow’s stewardship program, which is quite 

similar to Monsanto’s stewardship program for RR crops.

• APHIS fails to provide any critical assessment of Dow’s stewardship plan.

• Evaluate the potential for the increased use of 2,4-D associated with the adoption of DAS 

corn and soybean events to exacerbate the problems of herbicide-resistant weeds by 

accelerating the evolution of 2,4-D resistant weed populations.

• The EnlistTM technology will not be an exclusive answer to resistance development, but 

will be an extremely important tool in the development of comprehensive, science-based 

approaches to resistance management.

• APHIS fails to provide any assessment of the special proclivity of HR crop systems, or 

DAS‐68416‐4 soybean in particular, to trigger evolution of resistant weeds. The rapid 

emergence of GR weeds in RR crop systems is evidence of the resistant weed‐promoting 

effect of HR crop systems in general and a proper analysis would have provided APHIS 

with important insights into the risks of resistant weed evolution in the context of the DAS‐

68416‐4 soybean system.

• Evaluate the potential for 2,4-D-resistant weeds in 2,4-D resistant cropping systems. 

APHIS must take into account the reasonably foreseeable impact of future 2,4-D resistant 

crop deregulations in analyzing the development of superweeds that are resistant to 2,4-D 

and “fop” herbicides. Multiple resistance will develop in response to widespread use of 

2,4-D in corn and soon, if approved, in soybean and cotton.

• Without effective herbicide options for controlling resistant weeds, growers are left with no 

choice but to re-introduce intensive tillage systems for weed management.

• Resistance to auxin herbicides has not been prevalent throughout the world (relative to 

other commonly used herbicides such as atrazine, imazethapyr, or glyphosate) due to at 

least three main reasons: (l) auxin herbicides have a complicated mode or action with 

multiple target sites (Kelley and Riechers, 2007), (2) weeds that evolve resistance to auxin 

herbicides have typically displayed a 'fitness cost', which means that the plant is less 

physiologically fit or less competitive in the absence of the herbicide in relation to wildtype 

(i.e., sensitive to 2,4-D) plants, and (3) auxin herbicides have rarely been used by 

themselves but are instead typically applied in tank mixtures.

Page 2-6
• Resistance to 2,4-D and dicamba represents no more a threat to agricultural production than 

resistance to other critical herbicides and the likelihood that it will be used in a manner 

consistent with best management practices is good.

• Stacking 2,4-D and dicamba tolerance with that of glyphosate, glufosinate, and other 

herbicide tolerant traits will further facilitate the use of these herbicides in a diversified 

program. Stacking herbicide traits does not in itself promote the evolution of resistance to 

more than one herbicide since, just as for individual herbicides, the evolution of resistance 

is a function of how the herbicides are used rather than a function of the selectivity of the 

crop to multiple herbicides.

5. Impacts Resulting from the Increase of Resistant Weeds 

• Assess the reasonably foreseeable impact of increased tillage, soil erosion, and herbicide 

use to control weeds that become resistant to 2,4‐D, quizalofop, and/or glyphosate.

• APHIS provides no meaningful assessment of the costs to farmers or U.S. agriculture from 

the reasonably foreseeable evolution of weeds resistant to 2,4-D or glufosinate.

• Provide assessment of the impacts or costs to farmers of past herbicide resistance that has 

triggered patterns of weed control, the use of herbicides, and the increased cost to farmers.

• Discuss the increasing costs and labor to combat resistant weeds that persist and spread in 

fields. 

• Because the development of herbicide-resistant weeds and volunteer corn are reasonably 

foreseeable impacts of 2,4-D resistant corn cultivation, the analysis needs to consider the 

negative impacts on conservation tillage.

• Herbicide‐resistant weeds lead directly to adverse impacts on farmers, the environment and 

public health. Adverse impacts include the increased costs incurred by growers for 

additional herbicides to control them, greater farmer exposure to herbicides, consumer 

exposure to herbicide residues in food and water, soil erosion, greater fuel use and 

emissions from increased use of mechanical tillage to control resistant weeds, 

environmental impacts from herbicide runoff, and in some cases substantial labor costs for 

manual weed control. These are some of the costs of unsustainable weed control practices, 

the clearest manifestation of which is evolution of herbicide‐resistant weeds. 

• As the spread of glyphosate-resistant weeds occurred, the adoption of tillage, including 

deep tillage with a moldboard plow has once again become more common. The return of 

conventional tillage has led to increased wind and water erosion. Neither 2,4-D nor 

dicamba technologies would eliminate tillage, but they would greatly reduce the need for 

deep tillage allowing many farmers to return to more reduced tillage production systems.

• APHIS must assess the potential for 2,4-D crop systems to foster resistance, not only to 2,4-

D, but also to dicamba, and the impacts such cross-resistant weeds (against a background of 

resistance to glyphosate, ALS inhibitors, and/or other herbicides), would have on weed 

control in soybeans, corn, and other crops. Known weed biotypes with resistance to either 

2,4-D or dicamba should be tested for tolerance to the other, to help establish the potential 

for such cross-resistance.

• APHIS must assess the potential for 2,4-D crop systems to further increase soil erosion 

through increased use of tillage to control the 2,4-D-resistant weeds that will be generated 

by these crop systems.

Page 2-7
6. Weed Resistance Management

• Evaluate in detail the farmer use of resistant-weed mitigation measures or effectiveness of 

the mitigation measures.

• Provide an assessment of weed resistance stewardship, including the flaws of past 

stewardship plans or how they might be improved.

• APHIS failed to consider that the value of crop rotation for suppressing weeds is 

undermined when rotated crops are resistant to the same herbicides.

• New and expanded uses of existing herbicides are needed for integrated weed management 

programs in order to mitigate weed resistance and meet our current and future crop 

production needs.

7. Volunteer Corn/Soybean

• Estimate the cost to farmers for controlling volunteer DAS‐ 40278‐9 corn which will 

become a problematic “resistant weed” in its own right by virtue of its resistance to two to 

four herbicides.

• Assess the dispersal of herbicide resistance traits via pollen or seed dispersal or its 

implications for stewardship practices.

• Dow discusses the potential for DAS-68416-4 soybean to cross with soybeans possessing 

other herbicide resistance traits to produce soybean volunteers with resistance to additional 

herbicides. Indeed, three different GE soybean events with resistance to dicamba 

(Monsanto), the HPPD inhibitor isoxaflutole (BASF), and imidazolinone herbicides 

(Bayer) are presently pending deregulation decisions by USDA (APHIS Pending Dereg 

2012). Such crossing could result in volunteer soybeans resistant to four or more classes of 

herbicide.

• Soybean is primarily a self-pollinating crop, but the potential for perhaps considerable 

cross-pollination is suggested by the frequency with which pollinators – bees (honeybees 

and wild bees), wasps, and flies – visit soybean fields (Anonymous 2012, O’Neal & Gill 

2012). Insect pollinators are known to effect pollination at considerable distances from the 

source plants, including from primarily self-pollinating crops (e.g. Pasquet et al. 2008).

• Even if soybean cross-pollination is relatively uncommon, it could give rise to problematic 

volunteer HR soybean control problems where it does occur, with the adverse 

consequences noted above.

• APHIS should consider scenarios with volunteers that have stacked resistance. The 

assessment should include increased costs of control, increased use of herbicides, increased 

weed resistance risks from a narrowing of herbicidal control options, and increased reliance 

on those (few) herbicides still effective.

• HR corn volunteers produce lower levels of Bt toxin and thereby promote Bt resistance in 

corn rootworm; the more HR traits in the corn volunteers, the less likely they will be 

managed adequately, and hence the more likely they will contribute to Bt resistance.

8. Impacts on Organic and Non-GE Crops

• Assess the socioeconomic impacts of transgenic contamination on the entire organic 

industry. 

Page 2-8
• Complete a full analysis of the economic impacts due to GE contamination for organic and 

non-GE growers. GE crops can cross-pollinate with non-GE crops, contaminating 

conventional or organic crops. This contamination can result in a rejection of loads by the 

Organic Trade Association, resulting in economic losses for farmers, previously estimated 

at 40 million dollars annually. APHIS needs to reevaluate the effect of DAS-40278-9 corn 

on organic corn, as cross-pollination may pose a plant pest risk. 

• Include an analysis of the cost of testing, tracing and separating DAS- 40278-9 corn and 

DAS-68416-4 soybeans to avoid contamination of non-GE crops and the subsequent impact 

on exports.

• Assess the potential impacts of deregulating 2,4-D-resistant corn on the supply of organic 

corn feed.

• Genetic admixture is an environmental concern that can cause the alteration of a plant’s 

deoxyribonucleic acid (DNA) by transmitting a GE gene to a non-GE plant, in turn, causing 

a loss of biodiversity that could result in the potential elimination or reduction of 

conventional and organic corn varieties.

• Evaluate the impact of deregulating 2,4-D resistant corn and the subsequent transgenic 

contamination on both the public’s and the grower’s ability to choose non-GE corn; and

consider individual choice or the social or economic impact of eliminating that choice.

• Evaluate the impacts of GE admixture through feed and food products on animal and 

human food chains, and related human health impacts.

9. Cumulative Impacts

• Address the potential cumulative environmental impacts resulting from reasonably 

foreseeable future crops with “stacked” genetic traits.

• Consider the cumulatively significant impacts of all synthetic auxin herbicide-tolerant 

crops.

• Impact analysis should consider drift not only from 2,4-D resistant corn, but also the use of 

2,4-D in other reasonably foreseeable 2,4-D-resistant GE crop systems that are now 

pending before APHIS.

• Assessment of the resistant weed impact of DAS-68416-4 soybean grown in rotation with 

EnlistTM corn.

• Dow plans to sell this GE 2-4,D soy “stacked” with resistance to glyphosate and glufosinate 

herbicides, yet neither Dow nor USDA has analyzed the potential synergistic or cumulative 

impacts that these planned combinations pose. Glufosinate has both reproductive and 

neurological toxicity to mammals, and on this basis is slated to be banned in the EU by 

2017.

• Assess the cumulative impacts of growing multiple HR crops, including changes in 

herbicide use patterns, weed resistance, human health effects, environmental effects from 

herbicide drift and runoff, and harm to wildlife, in particular threatened and endangered 

species and their critical habitats.

• APHIS must take into account any reasonably foreseeable impacts of conferring multiple 

herbicide-resistant traits via stacking of different resistance traits in the same crops, 

growing crops with different resistance traits in the vicinity of each other within a given 

year, and using the same resistance traits in rotation crops, for example.

Page 2-9
The following issues related to herbicide use were identified from public comments. As noted, 

above, herbicide use is regulated by EPA. EPA is evaluating DAS' submission for their new 2,4-D 

choline salt formulation and will be making those assessments available to public. Therefore, these 

issues are listed here but for the most part are not being addressed in this EIS. When these issues 

are covered, they are included in the Appendices.

Herbicide Use and Impacts from Herbicide Use

• Examine the potential for increased use of 2,4-D, glyphosate, glufosinate, and quizalofop 

associated with deregulation of DAS-40278-9 corn, DAS-68416-4 soybean, and DAS44406-6 soybean. Consider the rate applied per application, number of applications per 

season, and number of acres planted.

• Project the shift in herbicide use patterns associated with DAS-40278-9 corn, DAS-68416-4 

soybean, and DAS-44406-6 soybean. 

• USDA has not thoroughly assessed the environmental risks associated with many of these 

transgenic crops. 2,4-D is a volatile herbicide, which can easily drift onto nearby crops, 

vegetables and flowers. In fact, a comparative risk assessment found that 2,4-D was 400 

times more likely to cause non-target plant injury than glyphosate.

• The transgene confers resistance to 2,4-D, glufosinate, and glyphosate, and in conjunction 

with the insertion site and genetic background of the host plant, determines how much 2,4-

D, glufosinate, and glyphosate can be applied and when during the growing season without 

injuring the crop. Thus the pattern of tolerance to the herbicide(s) is event-specific and 

should be described by the applicant in the Petition, and the implications rigorously 

explored by APHIS in a robust analysis pursuant to the National Environmental Policy Act 

(NEPA) and the Plant Protection Act.

• Compare increased herbicide use to conventional varieties.

• APHIS must disclose and analyze the impacts of herbicides used on a deregulating DAS40278-9 corn on both organic and conventional non-GE corn.

• Fully address impacts from the shift of use rates among different herbicides that may 

accompany deregulation of DAS-40278-9 corn, DAS-68416-4 soybean, and DAS-44406-6 

soybean.

• Provide a detailed examination of the cumulative effects of stacking 2,4-D resistant corn 

with other herbicide tolerances. 

• Acreage likely to shift in herbicide use from glyphosate to synthetic auxin herbicides is not 

identified. 

• If an engineered crop is immune to injury even at rates higher than allowed by label or at 

later times in development, experience has shown that growers will push or exceed the 

label limits in situations where there is weed pressure. APHIS needs to explore the 

implications of removing biological constraints to herbicide use in their assessments.

• USDA must consider the biological opinion of the National Marine Fishery Service 

regarding 2,4-D registration.

• Benefits of 2,4-D technology for the Georgia cotton grower would include: 1) Improved 

weed control; 2) Prevention of additional herbicide resistance development; 3) Reduction in 

herbicide use; and 4) Reduction in tillage, wind erosion, and soil erosion.

Page 2-10
• An enormous amount of research by the registrants and other weed scientists around the 

world has been conducted to develop methods to minimize the potential for off-target 

movement. These efforts include 1) improving herbicide formulations, thereby reducing 

volatility and/or drift, 2) improving application equipment techniques and application 

methods, thereby reducing drift, and 3) developing educational materials to assist growers 

in reducing off target movement when making pesticide applications. There is no question 

these research efforts will greatly minimize off-target movement of all pesticides, not just 

2,4-D and dicamba, and will greatly improve the ability of a grower to apply pesticides that

stay in the targeted area.

• APHIS must project the impact of 2,4-D-resistant corn and soybean systems (with 

additional resistance to glyphosate and/or glufosinate) in further reducing populations of 

milkweed in agricultural fields and thus exacerbating the decline in Monarch populations.

• APHIS must assess the impacts of 2,4-D-resistant corn and soybean systems (with 

additional resistance to glyphosate and/or glufosinate) on amphibian populations.

Herbicide Use - General 

• Any questions or concerns about the use of 2,4-D in a 2,4-D-tolerant soybean cropping 

system should continue to be addressed through the authority of the Environmental 

Protection Agency (EPA) to regulate the safe use of registered herbicides.

• Assess potential impacts to animals in fields of DAS‐68416‐4 soybean in light of the 

foreseeable increase in exposure to herbicides and their metabolites based on realistic use 

scenarios and a wide range of relevant independent scientific studies in order to compare 

alternatives.

• Assess the potential of the EnlistTM corn and soybean systems to increase drift-related crop 

injury as well as potential mitigation measures.

• Assess the negative environmental impacts of pesticide drift associated with the prevalence 

of glyphosate-resistant weeds.

• Assess cumulative impact of a combination of herbicides on water resources, including the 

impacts to surface water from off-site movement of herbicides.

• APHIS should consider late, off-label treatment of crops, and include protection of insects, 

birds, reptiles, amphibians or other animals.

• Examine impacts that increased herbicide use in DAS‐68416‐4 soybean would have on 

those nearby habitats.

• The potential impact on the plant population diversity within treated fields of DAS-40278-9 

corn and the resulting impacts to animals from those changes should be evaluated.

• Concerns about the impacts to plant and animal biodiversity in and around cornfields from 

increased pesticide use due to implementation of DAS-40278-9 crop systems.

• The estimated increase in herbicide use would likely jeopardize species and critical habitats 

protected under the Endangered Species Act (ESA). A “failure by USDA to recognize the 

risks of jeopardizing endangered species and adversely modifying their critical habitats 

would not be in compliance with the statutory requirements of the National Environmental 

Policy Act (NEPA).”

• Dow plans to sell this GE 2-4,D soy “stacked” with resistance to glyphosate—the active 

ingredient in Roundup—and glufosinate herbicides, yet neither Dow nor USDA has 

Page 2-11
analyzed the potential synergistic or cumulative impacts that these planned combinations 

pose.

• The ability to effectively control weeds is one of the most important factors in profitable 

crop production. The use of glyphosate in Roundup Ready crops was a highly costeffective approach to weed control for many years, but heavy reliance on glyphosate-only 

weed control programs eventually led to the development of glyphosate resistant weeds, 

including marestail, waterhemp, Palmer amaranth, kochia and giant ragweed, that are 

difficult to control with current technologies. 

• Weed management will be much more successful if post-emergence 2,4-D treatments are 

used in conjunction with pre-emergence residual herbicides that can provide extended 

control. The use of pre-emergence herbicides as part of an integrated approach has 

increased in recent years due to the difficulties of controlling glyphosate resistant weeds 

and because of the improved commodity prices. This approach helps minimize potential for 

early season weed competition and provides more flexibility and better efficacy with the 

post-emergence treatment. The other huge benefit is that by utilizing more herbicide modes 

of action, the risk of developing herbicide resistant weeds is greatly diminished.

Herbicide Use - 2,4-D

• Assess impacts associated with the potential increases in use of 2,4-D, quizalofop, and their 

metabolites on non-target animal communities, particularly on the honeybee population.

• Thoroughly evaluate the likely increase in 2,4-D application, along with the associated 

environmental and public health impacts.

• Adequately account for the unique risks associated with 2,4-dichlorophenoxyacetic acid 

(2,4-D) herbicides.

• Evaluate health risks posed by drift of 2,4-D onto unsuspecting victims. There is no worse 

herbicide for drifting long distances and damaging fruit and vegetable plants than 2,4-D, 

and the introduction of these resistant varieties will make it far more likely that such drift 

will be occurring with increasing frequency in the future. For some growers, it will make 

their livelihoods untenable and for homeowners in the country, they will see increasing 

damage of their gardens and trees of 2,4-D drift.

• APHIS and EPA must assess the increased incidence of disease to be expected with the 

substantial increase in 2,4-D use accompanying introduction of these crop systems.

• Farmers have a long history of successfully using proper equipment and application 

procedures to avoid and minimize off-target movement of herbicides. Similarly to other 

herbicide products, off-site movement of 2,4-D can be prevented through proper 

stewardship, application techniques, equipment settings and consideration of environmental 

conditions during application, such as wind speed..... newer 2,4-D formulations have been 

developed to substantially reduce volatility compared to first-generation products. We are 

also pleased that the petitioner has addressed the potential for off-site movement by 

prohibiting aerial applications and implementing specific environmental and equipment 

application requirements on the 2,4-D label, including a wind-directional buffer when 

sensitive areas are present, and the use of low volatility 2,4-D formulations.

• Adequately assess the potential for an increased health risk to farmers and farmworkers 

using 2,4-D.

Page 2-12
• APHIS needs to reconsider potential risks to animal communities from eating DAS-68416‐

4 soybean tissues or drinking runoff containing residues of 2,4-D and the unique 

metabolites.

• The developer in the future may petition the EPA for an increased tolerance for 2,4-D 

simply because residues increase with increased 2,4-D use, and that APHIS should consider 

the health implications of such higher levels of 2,4-D likely to be found in food. USDA 

must consider the effects that higher 2,4-D residues in food would have on human health.

• Account for the risks associated with 2,4-D and their severity relative to the potential harm 

associated with other herbicides.

• Increase in 2,4-D use would increase the amount of herbicide in surface waters, adversely 

impacting drinking water quality. This will have implications for fragile wetland areas, 

especially those under conservation.

• Impacts need to be assessed not only for the direct toxicity of the herbicides (2,4-D and 

quizalofop) and their metabolites on animal communities, but also for animals that may be 

indirectly exposed by over-spraying, brushing up against newly sprayed foliage, or feeding 

on corn leaves that may receive a higher dose of herbicide, as well as drinking surface 

water potentially impacted from surface runoff containing the herbicides. 

• APHIS must comprehensively assess the increased drift damage that would occur with 

various 2,4-D-resistant corn and soybean adoption scenarios, both in terms of lost yield and 

income, broken down by major crop (e.g. soybeans, cotton) or crop category (e.g. 

vegetables). APHIS should further assess the extent to which 2,4-D-resistant crop adoption 

would reduce plantings of susceptible crops (e.g. vegetables, grapes) and/or shift acreage to 

2,4-D- tolerant crops that could withstand drift level doses (e.g. corn).

• APHIS must account for the inevitable use of more drift-prone 2,4-D formulations (e.g.,

because likely to be cheaper than the choline salt), and not presume an ideal world scenario 

where only potentially less drift-prone formulations are used.

Herbicide Use – Glufosinate

• Analyze the health impacts stemming from the expected increase in use of glufosinate.

• Glufosinate poses significant ecological risks to non-target plants and animals and the 

implications from increased use as a result of the determination of nonregulated status of 

DAS-68416-4 Soybean should be included in the EA. 

• Analyze the potential impact from the metabolite of glufosinate, 

methylphosphinicopropionic acid (MPPA), which could also pose human health risks, 

especially to pregnant women and their fetuses. Research should be completed on this 

metabolite to ensure that it will not be detrimental to wildlife, especially those plants and 

animals protected by the Endangered Species Act.

Herbicide Use – Quizalofop

• Need complete information on the environmental impacts of 2,4-D and quizalofop.

• Perform human health assessment of the occupational exposure to quizalofop

• Assess impacts associated with the potential increases in use of 2,4-D, quizalofop, and their 

metabolites on non-target animal communities, particularly on the honeybee population.

Page 2-13
• Impacts need to be assessed not only for the direct toxicity of the herbicides (2,4-D and 

quizalofop) and their metabolites on animal communities, but also for animals that may be 

indirectly exposed by over-spraying, brushing up against newly sprayed foliage, or feeding 

on corn leaves that may receive a higher dose of herbicide, as well as drinking surface 

water potentially impacted from surface runoff containing the herbicides.

• Synergistic effects of the combined use of 2,4-D and quizalopfop have not been considered 

for the increased ecological risks.

Herbicide Use - Dioxin Impurities in 2,4-D

• USDA and EPA should conduct an assessment of the greatly increased exposure to dioxins 

that would be triggered by EnlistTM soybeans and corn in light of EPA’s ongoing review of 

dioxin toxicity, both cancer and non-cancer risks.

• Include analysis for the health impacts from dioxin contamination in 2,4-D. Impacts to 

human reproduction and to workers from exposure to dioxin (especially 2,3,7,8-TCDD) 

have not fully been considered and analyzed and request that these impacts be analyzed.

• Assess potential short- and long-term impacts on animals from the dioxin impurities, as 

well as 2,4-D.

• Evaluate potential effects of the dioxin impurities on treated pollen from DAS-40278-9

corn on honeybees and other animal populations that are in contact with/collect pollen.

• Need cumulative effects on human health and environment from dioxin and potential 

effects on surface water quality and non-target plants and animals (including endangered 

species).

• Assess the increased dioxin emissions and exposure associated with incineration of 

unrinsed 2,4-D containers that would result from the vastly increased use of 2,4-D with 

EnlistTM soybeans and corn.

• USDA should conduct or commission independent dioxin testing of 2,4-D formulations.

Herbicide Use - 2,4-D Metabolites

• APHIS failed to fully consider the impacts of increased 2,4-D use, related DCP-conjugates, 

and increased glyphosate.

• APHIS needs to consider the impacts to human health of exposure to DCP and DCP 

conjugates that are a result of the activity of the engineered AAD-12 enzyme in DAS68416-4 soybean.

• The types and levels of DCP and DCP conjugates in DAS‐68416‐4 soybean forage and hay 

after 2,4‐D applications need to be compared with independent research on 2,4‐D and DCP 

metabolism in conventional soybeans (Pascal‐Lorber et al. 2003), with any differences 

explained. 

• DCP conjugates were not included in the evaluation of whether DAS-40278-9 corn will 

meet tolerance requirements in forage and fodder, and suggested that, if DCP conjugates 

had been included, with the assumption of similar toxicity to free DCP, tolerance levels 

would be exceeded

• APHIS should consider levels of all expected toxic residues and metabolites; and assess 

impacts to non‐target organisms of the novel, potentially toxic constituents expected to 

Page 2-14
result when 2,4‐D with DAS‐68416‐4 soybeans under a variety of anticipated application 

scenarios.

• Evaluate potential impacts of pollen containing residues and metabolites not found in 

conventional pollen that might make it toxic to organisms that come in contact with it.

• APHIS did not take into account independent research and Dow studies showing that 

potentially toxic metabolites do occur as a result of the engineered trait. USDA should 

carefully consider the impacts of the accumulation of novel molecules with similarity to 

known toxins in DAS-68416-4 soybean. APHIS needs to know if the AAD-12 enzyme 

alters metabolism in DAS-68 416-4 soybean such that the plants have a new composition 

after 2,4-D is used, and thus have the potential to harm non-target species. APHIS must

consider whether DCP and its conjugates are present in soluble fractions of DAS-68416-4 

soybeans after AAD-12 enzyme acts upon 2,4‐D in order to fully assess the impacts to nontarget organisms and on human health.

• APHIS should consider whether DCP and its conjugates are present in soluble fractions of 

DAS-40278‐9 corn after the AAD‐1 enzyme acts upon 2,4-D in order to fully assess the 

“plant pest risks” to non-target organisms

• Consider the possible toxicity of the metabolites that are present in DAS-40278-9 corn 

exposed to herbicide substrates of the ADD-1 protein, and the impact of this toxicity to 

listed species requiring formal USFWS consultation.

• Information on the herbicide residues and metabolites in plant tissues from the time of 

application through post-harvest should be available for review by APHIS and the public

Page 2-15
Table 2-1. EIS Public Scoping Comments Submitted Online

Comment # Comment ID Commenter Comment Excerpt Topic Area

1 APHIS-2013-

0042-0002

Jean Public The American Public wants this permit denied. Monsanto and Dow 

are releasing harmful items to the American Public with these 

unregulated soybean and corns.

N/A

2 APHIS-2013-

0042-0003

Carl Bausch

Undertaking the National Environmental Policy Act process for the 

identified petitions is both wasteful and superfluous.

N/A

Granting (with or without conditions) or denying a petition does not 

constitute “alternatives” to be considered in the NEPA process; 

rather, they are decision options for the agency. Alternatives that 

must be considered under NEPA relate directly to the purpose and 

need for a proposed action, the statement of which, again, is missing 

from the notice. 

3 APHIS-2013-

0042-0004

Illinois Farm 

Bureau (IFB) –

Philip Nelson

These traits have already gone through USDA's rigorous regulatory 

review protocol and there have been no scientific, findings to 

warrant additional EIS. On behalf of nearly 83,000 Illinois farmers, I 

write today to request-that, APHIS move expeditiously when 

completing this seemingly superfluous regulatory review.

Biotechnology has produced vast improvements in farm production 

practices, permitting farmers to do more with less. Herbicidetolerant seeds are simply another tool for our producers to utilize 

towards helping feed the world's ever increasing population. These 

technologies will have a positive impact on farming and the food 

that we produce.

4 APHIS-2013-

0042-0006

U.S. Department of 

Interior, National 

Park Service –

Roxanne Runkel

The National Park Service supports the objective identified or 

development of science that addresses the Environmental Issues for 

Consideration identified o pages 28799 [of the Federal Register 

notice]. The NPS is concerned about the indirect effects on the soil 

and water quality in NPS areas as a result of increased herbicide use. 

We believe the indirect effects on soil and water quality as a result 

of increased herbicide use of the products proposed to be deregulated, be evaluated.

Herbicide use -

effects on soil and 

water

5 APHIS-2013- Louis Metzman I implore you to not approve release of 2,4-D resistant plants. I have Herbicide drift

Page 2-16
Comment # Comment ID Commenter Comment Excerpt Topic Area

0042-0007 (grower) had collateral damage from 2,4-D drift to my fruit orchard and my 5 

acre tree planting and to landscape plants at my house 6 times over 

the past 14 years - this is a very dangerous herbicide that tends to 

vaporize and cause damage to neighboring plants. This damage is all 

too common with this particular herbicide. 

Forester Mike Warner, with Mike Warner ARBORTERRA 

Consulting, tells me he has been asked to check on 15 claims of 

what he feels are 2,4-D damage so far this year. I can only imagine 

the damage we will see with more widespread use of this very 

dangerous chemical. It causes damage very far away to plants - how 

will we know who did the damage, and how will we hold them 

responsible? And, with no accountability, they can spray with 

impunity. Also, perhaps in future years we will find out it was also 

harmful to the people who are also exposed to it.

6 APHIS-2013-

0042-0009

David Ortman • The EIS should include an alternative prohibiting field 

testing of herbicide resistant corn and soybeans.

• The EIS should provide an estimate and analysis of the 

quantities of 2,4-D and glyphosate that would enter 

watercourses and waterbodies, including within our nation’s 

coastal zone, under alternatives that would ban herbicide 

resistant corn and soybeans; that would continue herbicide 

resistant corn and soybeans as regulated articles; and under 

Dow AgroSciences LLC’s request for nonregulated status.

• The EIS should set out a testing protocol for determining the 

level of Glyphosate and 2,4-D in water bodies in order to 

establish a baseline for future evaluations of Glyphosate and 

2,4-D use due to “herbicide resistant” corn and soybeans.

• The EIS should set out a testing protocol for determining the 

level of Glyphosate residues in shellfish and fish to assure 

that residue tolerances are not exceeded and to ensure that 

Page 2-17
Comment # Comment ID Commenter Comment Excerpt Topic Area

2,4-D residues are not present.

7 APHIS-2013-

0042-0011

Carl Bausch • Where specifically in chapter 104 of title 7 of the United 

States Code is APHIS authorized to regulate the introduction 

(importation, interstate movement, or release into the 

environment) of genetically engineered organisms and 

products?

• Why does APHIS feel it is necessary to undertake a costly 

(to industry and taxpayers), unnecessary environmental 

impact statement process when a conventional risk 

assessment establishes that the organism is not a plant pest 

and that APHIS therefore lacks jurisdiction (see my earlier 

comment for explanation)?

• The statement of purpose and need is missing from the 

notices. To what need and for what purposes are petitioners

responding in developing and commercializing their 

products? The answer to this question largely determines the 

range of reasonable alternatives the agency must consider in 

the NEPA process.

• Granting (with or without conditions) or denying petitions 

does not constitute “alternatives” to be considered in 

NEPA’s environmental impact statement process; rather, 

they are decision options for the agency (see my earlier 

comment for explanation). Alternatives that must be 

considered under NEPA relate directly to the purposes of and 

need for proposed actions.

• APHIS NEPA documents are not written in plain language, 

as required by the NEPA implementing procedures (40 

C.F.R. § 1502.8). 

• Monitoring, which is an essential component of the NEPA 

process (40 C.F.R. § 1505.3), should be employed in 

biotechnology permitting to confirm assumptions made in 

NEPA documents and respond to many unanswered, but oftPage 2-18
Comment # Comment ID Commenter Comment Excerpt Topic Area

repeated questions.

• APHIS has often claimed that, although individual farmers 

may be affected by releasing genetically engineered 

organisms in the area, when examined in total, none of the 

potential business losses is expected to be so severe as to 

amount to a significant impact. This determination fails to 

recognize that environmental “significance” exists at all 

levels―“society as a whole (human, national), the affected 

region, the affected interests, and the locality.” 40 C.F.R. § 

1508.27(a).

• APHIS tends to rely on the United States Environmental 

Protection Agency’s (EPA) consideration of environmental 

effects in the context of the Federal Insecticide, Fungicide 

and Rodenticide Act (FIFRA) registration process, as well as 

FDA’s determinations under its enabling legislation. The 

regulatory and review processes of EPA and FDA cannot be 

relied upon to relieve APHIS from considering in the context 

of the National Environmental Policy Act (NEPA) process 

any and all effects associated with release into the 

environmental of petitioners’ products. 

• In the past, APHIS appears to have placed a great deal of 

reliance on petitioners in complying with NEPA. Agencies 

have a responsibility under NEPA to independently 

investigate and assess the environmental impacts of 

proposals under consideration (40 C.F.R. § 1506.5(a) and 

(b)). 

• There is considerable uncertainty regarding potential 

environmental effects of releasing genetically engineered 

organisms. Although an agency is not precluded from 

approving a particular proposal involving substantial 

uncertainty, it must disclose all areas of uncertainty. Save 

Our Ecosystems v. Clark, 747 F.2d 1240, 1246 (9th Cir. 

Page 2-19
Comment # Comment ID Commenter Comment Excerpt Topic Area

1984).

• The taxpayer and the agricultural biotechnology industry 

would be better served if APHIS announced it would no 

longer “regulate” agricultural biotechnology because there 

has not been a proven plant-pest risk associated with the 

technology in decades, perhaps ever.

APHIS-2013-

0042-0010 Carl Bausch Duplicate of comment APHIS-2013-0042-0003 N/A

8 APHIS-2013-

0042-0012

Tess Cramer Once GMO's are introduced into the environment, there is no way to 

recall them OR their genetic pollution to organic crops.

N/A

9 APHIS-2013-

0042-0013

Arthur Tesla These plants will turn up as volunteer weeds in other farmers fields Plant 

Communities

10 APHIS-2013-

0042-0014

MS Lower glyphosate and Round Up now. Do not do what you're 

planning on doing, EPA and raise the limits. It's already at very 

toxic levels and raising the limits of poison is not only going to be 

doing the exact opposite of what you're supposed to be in your job 

but the very exact opposite. Do not allow your ethics and conscience 

from deep within to be override by greed and money. Do what's 

right for the environment and protect it.

Herbicide use –

glyphosate limit

11 APHIS-2013-

0042-0015

Renae Hockaday • Why is nonregulation even being considered?

• There's too much impact on people's health and neighboring 

(organic and non) producers.

• To put GMO into foods without being listed as GMO in the 

ingredients is blatant dishonesty. At the very least products 

from GMO must be listed in the ingredients label.

FDA - labeling

12 APHIS-2013-

0042-0016

Jordan Scheibel 

(grower)

• There is no worse herbicide for drifting long distances and 

damaging fruit and vegetable plants than 2,4-D, and the 

introduction of these resistant varieties will make it far more 

likely that such drift will be occurring with increasing 

frequency in the future. For some growers, it will make their 

livelihoods untenable and for homeowners in the country, they

Herbicide use -

drift

Page 2-20
Comment # Comment ID Commenter Comment Excerpt Topic Area

will see increasing damage of their gardens and trees of 2,4-D 

drift.

• The introduction of these varieties is an implicit admission that 

glyphosate resistant varieties are failing, weeds are becoming 

resistant, and stronger herbicides are needed. I shudder to think 

what herbicides will be necessary in 5 or 10 years as herbicide 

resistance continues to grow and the regulatory bodies that are 

supposed to be considering the long term implications of 

introducing these herbicide resistant varieties continue to 

rubber stamp them. 

13 APHIS-2013-

0042-0017

Martin Johnstone As there is no actual requirement for GM food, what makes you think 

you have the right to impose it upon the people without asking them if 

they want it? Is this the case: Ask the people if they want GM 

products. You will never ask, because you know the answer will be no. 

Therefore you continue without asking, forcing people to 'accept' your 

products? You don't have the right to do that.

N/A

14 APHIS-2013-

0042-0018

Arthur Tesla History has shown these crops will appear as volunteer weeds in 

farmers fields and be difficult to control because they are herbicide 

resistant/ They are plant pests!

They are also plant pests to consumers who don't want to eat these 

Dangerous genetically engineered foods.

Plant 

communities -

volunteers

15 APHIS-2013-

0042-0019

Anonymous 

Against Crop 

Oppression

America does not want to purchase biotechnology as a food source 

or fuel source. Europe does not want to purchase biotechnology as a 

food source or fuel source. The rest of the world does not want to 

have biotechnology as a food or fuel source imposed on them. There 

is no market for genetically modified, genetically engineered, 

genetically enhanced or altered food crops used for food or fuel.

N/A

16 APHIS-2013-

0042-0020

Klaas Raater Please consider the environmental impact of every country in the world 

hating America for its corporate fascism. I am already boycotting every 

American product. The same goes for my family and my friends. You 

have alienated yourself from the rest of the world. Way to go America! 

N/A

Page 2-21
Comment # Comment ID Commenter Comment Excerpt Topic Area

And i will not even spend a single holiday at your country anymore for 

the rest of my life. You want war with the rest of the world? No 

problem, you got it! I'd rather die than eat your Frankenfoods!

17 APHIS-2013-

0042-0021

Doris Headley For some time now, knowing that what I purchase was produced in 

North America or the UK was my only safety net. If you take that 

away, I shudder to think what I could be consuming.

N/A

18 APHIS-2013-

0042-0022

Marina Vrouvlianis Stop poisoning the world N/A

19 APHIS-2013-

0042-0023

Tanya Molyneux Weeds are becoming resistant to the chemicals we treat them with and 

the answer to just apply more herbicide is poisoning our ground and 

drinking water, the food that we feed to our animals and the food we 

are eating. Stop the insanity before its too late for the human race.

N/A

20 APHIS-2013-

0042-0024

JS Deran I am against any increase in herbicide resistant corn and soybeans. I 

don't think these crops should be allowed at all. I have seen the nonbiased reports from France and read of problems on farms and 

ranches in many countries that used GE crops. I think that all the 

herbicide resistant corn and soybeans should be banned from use. 

There is so much evidence that shows these crops to be detrimental 

to people AND animals that to allow further use should be criminal.

N/A

21 APHIS-2013-

0042-0025

Donna Deran Weeds treated with Glyphosate have become stronger from 

exposure so now they want to treat the SUPER weeds with more 

Glyphosate and then what will we have? Toxic wastelands with 

FRANKENWEEDS that nothing can kill!!! When will this madness 

stop? Our land and food are already contaminated with this chemical 

and now they want to make it worse by increasing allowable toxic 

exposure!!! JUST SAY NO !!! The EPA's first job is supposed to be 

protecting people from harmful toxins, not selling us out for the BIG 

BUCKS, from BIG CHEMICAL companies.

N/A

22 APHIS-2013-

0042-0026

Dale Moore -

American Farm 

Bureau Federation 

(Farm Bureau)

Farm Bureau respectfully asks APHIS to abide by the Ninth 

Circuit’s interpretation of its legal obligations under the PPA and 

NEPA and reconsider its decision to prepare EISs for the herbicide 

tolerant crops identified in the Notices. Farm Bureau asks APHIS to 

Oppose 

preparation of 

EIS

Page 2-22
Comment # Comment ID Commenter Comment Excerpt Topic Area

act expeditiously to finalize the deregulation process for these crops 

in keeping with the Ninth Circuit’s recent RRA decision and the 

APHIS regulations governing deregulation petitions.

23 APHIS-2013-

0042-0027

Drew Kershen (The 

University of 

Oklahoma, College 

of Law)

• If these seeds and plants are not plant pests, USDA-APHIS 

should deregulate without further study.

• In the Notices for both docket items, USDA-APHIS indicates 

that concerns about weed resistance related to herbicide usage 

is the driver behind the Notice to complete EISs. Yet, under 

statutory authority, EPA, through FIFRA, has the authority to 

regulate herbicides, including taking into account the 

environmental impact of weed resistance issues. EPA has 

exercised its authority under FIFRA and has authorized 

dicamba and 2,4-D has herbicides. When EPA exercises its 

authority under FIFRA, the EPA has performed an 

environmental analysis that is “functionally equivalent” to an 

EIS under NEPA.

Oppose 

preparation of 

EIS

24 APHIS-2013-

0042-0028

A. Stanley 

Culpepper -

University of 

Georgia, Weed 

Scientist, and 

grower

Cotton weed management programs in Georgia have undergone, and 

are continuing to undergo, significant changes. Currently 

recommended programs are complex, costly, and challenging to 

implement in a timely fashion. Growers are desperately in need of new 

technologies to improve control of Palmer amaranth, reduce the 

potential for further herbicide resistance development to currently used 

tools, and to reduce the economic burden that Palmer amaranth is 

placing on the agricultural industry. 

We admire and respect the desire of USDA and EPA to be certain 

that no agriculture technology will negatively impact the consumer, 

the user, or the environment in which we and our children live. Our 

request is simple, if deemed safe please assist in the movement of all 

new technologies to our growers as rapidly as feasible.

APHIS-2013-

0042-0028

A. Stanley 

Culpepper -

• Herbicide-resistance has significantly changed agriculture 

forever in the Southeast; especially for cotton growers. To 

Page 2-23
Comment # Comment ID Commenter Comment Excerpt Topic Area

University of 

Georgia, Weed 

Scientist, and 

grower

combat this pest, growers have relied heavily on herbicides, 

tillage, and hand weeding. Herbicide use in cotton has 

increased sharply with 2.5-times more herbicide active 

ingredient applied to cotton following the confirmation of 

glyphosate resistance in Palmer amaranth as compared to 

before documented resistance. Although grower herbicide 

input costs have more than doubled following the evolution 

and spread of glyphosate resistance, Palmer amaranth control 

is still not adequate. Thus, 92% of Georgia cotton growers 

hand-weed 52% of the crop with an average cost of $23 per 

hand-weeded acre, which is an increase of at least 475% as 

compared to hand weeding costs prior to resistance. In 

addition to increased herbicide use and hand weeding, 

growers in Georgia have indicated that they are using 

mechanical, in-crop cultivation (44% of acres), tillage for the 

incorporation of preplant herbicides (20% of the acres), and 

deep turning (19% of the acres every three years) to aid in 

Palmer amaranth control. Current weed management systems 

are extremely diverse, complex, less environmentally 

friendly, and costly when compared to those systems 

employed only a decade ago. Growers are in desperate need 

of new technologies that will aid in the management of 

glyphosate-resistant Palmer amaranth, and other problematic 

weeds, for long term sustainability.

APHIS-2013-

0042-0028

A. Stanley 

Culpepper -

University of 

Georgia, Weed 

Scientist, and 

grower

Benefits of 2,4-D or Dicamba Technologies For the Georgia Cotton 

Grower: 

1. Improved Weed Control: Neither dicamba nor 2,4-D are 

consistently effective in controlling Palmer amaranth larger 

than 4 inches when applied alone (Culpepper et al. 2010; 

Culpepper et al. 2011; Merchant et al. 2011); however, weed 

management systems including these herbicides are more 

consistently effective than current standards (Braxton et al. 

Page 2-24
Comment # Comment ID Commenter Comment Excerpt Topic Area

2010; Beckie 2011; Merchant et al. 2013; Richburg et al. 2012; 

Shaw and Arnold 2012). Weed management programs 

including 2,4-D or dicamba would improve a grower’s ability 

to manage this problematic weed in the following ways: 1) 

improved consistency in weed control especially on dryland 

production acres where residual herbicides often are not 

activated with rainfall at planting time, 2) more flexibility with 

herbicide application timings because glufosinate plus dicamba 

or 2,4-D will consistently control Palmer amaranth up to 6 

inches in height (at least 2 inches larger than todays standards), 

3) less herbicide carryover to subsequent crops because 

growers would be less dependent on long lasting residual 

herbicides, and 4) less yield loss from Palmer amaranth crop 

competition for light, nutrients, and water (Coetzer et al. 2002; 

Culpepper et al. 2010; Merchant et. al 2013; MacRae et al. 

2013).

2. Prevention of Additional Herbicide Resistance Development: 

USDA has voiced concerns that growers may adopt 2,4-D or 

dicamba technologies and rely too heavily on these herbicides 

thereby developing an even greater weed resistance scenario. 

Science has clearly shown that there is risk of resistance 

development to all herbicides; dicamba and 2,4-D are no 

exception. In fact, weeds have developed resistance to nearly 

all forms of weed management including herbicides, tillage, 

mowing and even hand weeding. Our data and surveys contrast 

the assumption that rapid development of resistance to 2,4-D or 

dicamba would occur in Georgia cotton. First, our data notes 

that since these auxin herbicides control only very small Palmer 

amaranth then they must be applied in tank mixtures with other 

herbicides such as glufosinate. Second, even mixtures of 

glufosinate plus 2,4-D or dicamba will only control Palmer 

amaranth less than six inches in height and since Palmer 

Page 2-25
Comment # Comment ID Commenter Comment Excerpt Topic Area

amaranth can grow as much as two inches per day selective 

residual herbicides must be used throughout the season. Simply 

put, data throughout the belt supports the fact that over-use 

and/or over-dependence of 2,4-D or dicamba in cotton would 

equal poor weed control and eventual crop failure which is a 

practice no grower would follow. Dicamba and 2,4-D would be 

an additional tool to include in the weed management program.

The greatest risk for developing herbicide resistance is actually 

occurring at this moment with the PPO herbicides and 

glufosinate. These products are being over used as growers 

have no other effective herbicidal options. New technologies 

such as dicamba or 2,4-D could be used to delay resistance 

development to the PPO herbicides and glufosinate and, in turn, 

systems could be developed using the PPO herbicides, 

glufosinate, 2,4-D, and dicamba extending the life of each of 

these chemistries. 

It is also critical to stress that, at least in Georgia, no weed 

management program relies exclusively on herbicides. The 

University of Georgia Weed Science Extension Team stresses 

to growers at more than 50 meetings each year that herbicides 

are only one part of the weed management program. 

Sustainability is only possible with the adoption and 

implementation of diverse management programs and Georgia 

growers have accepted this message as fact (Sosnoskie and 

Culpepper 2013). Growers are using programs that are complex 

and diverse integrating herbicides, hand weeding, and tillage or 

cover crops. Neither dicamba nor 2,4-D would change this 

approach but would simply be an additional tool to add into 

these management systems.

3. Reduction in Herbicide Use: Glyphosate-resistant Palmer 

amaranth has increased herbicide pounds of active ingredient 

applied in Georgia cotton by a factor of 2.5 when compared to 

Page 2-26
Comment # Comment ID Commenter Comment Excerpt Topic Area

herbicide use prior to resistance (Sonoskie and Culpepper 

2013). Programs developed by the University of Georgia for 

2,4-D or dicamba technologies suggest the pounds of herbicide 

active ingredient may be able to be reduced by at least 30% 

while actually providing better weed control; similar results are 

also noted in other areas across the cotton belt (Edwards et al. 

2013; Merchant et al. 2013; Smith and Hagood 2013; Steckel et 

al. 2013). 

4. Reduction in Tillage, Wind Erosion, and Soil Erosion: As 

the spread of glyphosate-resistant Palmer amaranth occurred, 

the adoption of tillage including deep turning of the land with 

moldboard plows has become common (Sosnoskie and 

Culpepper 2013). The return of conventional tillage has led to 

increased wind and water erosion. Neither 2,4-D nor dicamba 

technologies would eliminate tillage, but they would greatly 

reduce the need for deep tillage allowing many growers to 

return to more reduced tillage production systems. This 

opportunity to return to reduced tillage systems would be in 

response to a more consistently effective management program.

APHIS-2013-

0042-0028

A. Stanley 

Culpepper -

University of 

Georgia, Weed 

Scientist, and 

grower

Concerns With 2,4-D- or Dicamba-Resistant Technologies: 

1. Off-Target Movement: Off target movement of 2,4-D and 

dicamba pose the greatest limitation to the adoption of either auxin 

technology. Although it is currently unknown what restrictions will 

be in place to minimize off-target movement by herbicide labels, an 

enormous amount of research by the registrants and other scientists 

across the world is being conducted to develop methods to minimize 

the potential for off-target movement. These efforts include 1) 

improving herbicide formulations, thereby reducing volatility and/or 

drift, 2) improving application equipment techniques and application 

methods, thereby reducing drift, and 3) developing educational 

materials to assist growers in reducing off target movement when 

Page 2-27
Comment # Comment ID Commenter Comment Excerpt Topic Area

making pesticide applications (Bagley 2013, Huff et al. 2013; 

Kendig et al. 2013; Magidow et al. 2013; Newsom et al. 2013; 

Reynolds et al. 2013, Sandbrink et al. 2013). Benefits from these 

efforts will be monumental in minimizing off-target movement of 

ALL pesticides, not just 2,4-D and dicamba, and will greatly 

improve the ability of a grower to apply pesticides that stay in the 

targeted area. In Georgia, the University of Georgia and the Georgia 

Department of Agriculture are currently developing additional 

methods to further minimize off-target movement of auxin 

herbicides and other pesticides. Also, a cooperative effort between 

The University of Georgia, Georgia Department of Ag, Agronomic 

Industry leaders, and Horticultural Industry leaders is underway to 

further define methods to minimize off-target movement.

25 APHIS-2013-

0042-0029

Andrew LaVigne -

American Seed 

Trade Association

The Notices of Intent published on May 16 identify two issues that led 

APHIS to conclude that EISs were required by NEPA – the 

development of herbicide-resistant weeds (i.e., weed resistance) and 

increased herbicide use. Both of these issues relate solely to the 

herbicides, such as 2,4-D and Dicamba, that would be available for use 

in conjunction with the crops modified to tolerate their application. As 

such, these issues are subject to the exclusive jurisdiction of the U.S. 

Environmental Protection Agency (“EPA”) under the Federal 

Insecticide, Fungicide, and Rodenticide Act (“FIFRA”) and are 

decidedly not subject to APHIS’s jurisdiction under the Plant 

Protection Act (“PPA”).

ASTA and its members support a science-based, federal environmental 

review process for new biotechnology seed products. That process 

must recognize the distinct products, federal actions, and statutory 

mandates of the regulatory agencies involved. We are concerned, 

however, that by basing its decision to prepare EISs on the potential 

environmental effects of the herbicides rather than the associated 

herbicide tolerant crops, APHIS has failed to recognize those 

Oppose 

preparation of 

EIS

Page 2-28
Comment # Comment ID Commenter Comment Excerpt Topic Area

distinctions. Moreover, the EIS preparation process will unnecessarily 

delay issuance of determinations of nonregulated status for these crops 

with no additional benefit to the environment.

26 APHIS-2013-

0042-0030

Danny Murphy -

American Soybean 

Association

Soybean farmers need new technologies such as 2,4-D-tolerant 

soybeans to increase yields, manage weed resistance and maintain 

profitability. In light of the recent ruling by the Ninth Circuit Court 

of Appeals on the Roundup Ready alfalfa case -- which confirmed 

that issues relating to the use of herbicides are the responsibility of 

the Environmental Protection Agency (EPA), not USDA – ASA 

strongly urges USDA to reconsider its decision to require an EIS. 

According to the Notice of Intent, USDA’s basis for conducting the 

EIS all relate to herbicide uses, and the recent Ninth Circuit decision 

made clear the Framework1 under which regulatory authority is 

allocated among USDA, Food and Drug Administration (FDA) and 

EPA, and where USDA has no jurisdiction over herbicides nor for 

consideration of herbicide impacts related to its obligations under 

the Plant Protection Act. Conducting a time-consuming analysis 

already within the responsibilities of other federal agencies will 

cause a significant delay in bringing needed technologies to growers 

and is not consistent with the Plant Protection Act and the 

Administrative Procedure Act. The Ninth Circuit decision leaves no 

doubt that USDA does not need to analyze herbicide resistance or 

other impacts related to herbicide use in connection with petitions to 

deregulate herbicide-tolerant crops. It remains EPA’s responsibility

to prescribe the conditions in which it may be used.

Further, the Ninth Circuit made clear that APHIS’ regulatory 

jurisdiction ceases once APHIS determines that a crop is unlikely to 

Oppose 

preparation of 

EIS

1 Congress allocated regulatory authority of biotechnology derived crops under the Coordinated Framework. 51 Federal Register 

23302-09. June 26, 1986.

Page 2-29

 
Comment # Comment ID Commenter Comment Excerpt Topic Area

pose a plant pest risk. The Court ruled, “If APHIS concludes that 

the presumptive plant pest does not exhibit any risk of plant pest 

harm, APHIS must deregulate it since the agency does not have the 

jurisdiction to regulate organisms that are not plant pests.” APHIS 

already has determined that EnlistTM soybeans are unlikely to pose a 

plant pest risk. Thus, proceeding with an EIS would be contrary to 

the decision of the Ninth Circuit.

APHIS-2013-

0042-0030

Danny Murphy -

American Soybean 

Association

With mounting pressure to manage resistant weeds, soybean growers 

need new multiple-mode-of-action weed management tools not only to 

preserve yields, but also to maintain the economic and non-pecuniary 

benefits realized from using the glyphosate-tolerant systems. Weed 

resistance is a well understood scientific phenomenon that is not 

unique to biotechnology or any other form of agriculture. Different 

herbicides attack weeds by different methods or “modes of action.” 

The delay that will result from preparation of the EISs as proposed by 

APHIS will deny growers the tools they need to prevent and combat 

weed resistance and maximize yields through the use of herbicides that 

have been shown to operate with differing modes of action. The 

proposed use of these herbicides in conjunction with the associated 

herbicide tolerant plants also supports the continued use of 

environmentally sustainable practices such as no-till and low-till 

farming. 

The introduction of soybeans tolerant to 2,4-D will allow an 

additional mode of action to be used in the system, allowing for 

better weed control and harvested soybeans with less foreign 

material from weed seeds, a valuable characteristic for processors.

Oppose 

preparation of 

EIS

Soybean growers 

need new 

multiple-modeof-action weed 

management tools 

Soybeans tolerant 

to 2,4-D will 

allow an 

additional mode 

of action 

APHIS-2013-

0042-0030

Danny Murphy -

American Soybean 

Association

While ASA appreciates concerns about off-target movement of 2,4-D, 

we are confident that farmers have a long history of successfully using 

proper equipment and application procedures to avoid and minimize 

off-target movement of herbicides. Similarly to other herbicide 

products, off-site movement of 2,4-D can be prevented through proper 

Page 2-30
Comment # Comment ID Commenter Comment Excerpt Topic Area

stewardship, application techniques, equipment settings and 

consideration of environmental conditions during application, such as 

wind speed. ASA is pleased that newer 2,4-D formulations have been 

developed to substantially reduce volatility compared to firstgeneration products. We are also pleased that the petitioner has 

addressed the potential for off-site movement by prohibiting aerial 

applications and implementing specific environmental and equipment 

application requirements on the 2,4-D label, including a winddirectional buffer when sensitive areas are present, and the use of low 

volatility 2,4-D formulations. ASA believes that when recommended 

label practices are followed, farmers of various crops can co-exist and 

prosper.

27 APHIS-2013-

0042-0031

Wenonah Hauter –

Food & Water 

Watch

The USDA’s Environmental Impact Statement, must include, at a 

minimum: 

• An analysis on how 2,4‐D‐tolerant corn and soybeans will 

facilitate more use of 2,4-D, leading to the evolution of 2,4-Dresistant weeds and the abandonment of conservation tillage 

practices;

• Data on the levels of dioxin that will likely be released due to 

an increase in 2,4-D use, and the potential cumulative effects 

on human health and the environment;

• Studies on the effects of increased application of 2,4-D on 

surface water quality and impacts on non-target plants and 

animals, including endangered species;

• A hard look at how the volatility of 2,4-D will result in more 

occurrences of pesticide drift into neighboring fields, affecting 

plant health and costing nearby farmers;

• Research on how the ingestion of foods manufactured from 

these crops will affect human health and how the continued use 

of the herbicide in agriculture could endanger agricultural 

workers and the general public; and

• A detailed examination of the cumulative effects of stacking 

• Herbicide use

• Evolution of 

2,4-Dresistant 

weeds

• Human 

health –

ingestion

• Cumulative 

effects of 

stacking on 

cost of 

contaminatio

n and 2,4-Dand 

glyphosateresistant 

weeds to 

non-GE 

farmers

Page 2-31
Comment # Comment ID Commenter Comment Excerpt Topic Area

2,4‐D‐tolerant corn and soybeans with other herbicide 

tolerances, including the costs of contamination to non‐GE 

farmers and the costs that 2,4‐D and glyphosate resistant weeds 

will impose on these growers.

APHIS-2013-

0042-0031

Wenonah Hauter –

Food & Water 

Watch

USDA’s Environmental Assessments for 2,4‐D‐tolerant corn and 

soybeans were inadequate for these genetically engineered traits 

because they failed to thoroughly cover the cumulative effects that the 

use of these chemicals under realistic projections. The chemical 

treadmill model cannot be continued indefinitely. Weed resistance to 

these chemicals will continue to abound and the application of more 

noxious herbicides will increase exponentially. These new corn and 

soybean varieties are not only unsafe and inefficient, but are a 

completely unsustainable solution to the broader problems caused by 

high-input production agriculture and associated environmental 

pressures.

Herbicide use

28 APHIS-2013-

0042-0032

Pam Johnson -

National Corn 

Growers 

Association

USDA has not offered any new scientific reason to justify the 

decision to prepare an EIS. APHIS identifies two issues for 

consideration in an EIS, namely possible development of weed 

resistance and increased herbicide use. However, APHIS’ regulatory 

authority is based in the Plant Protection Act and the agency’s 

oversight is limited to evaluating the potential for the GE plant to 

pose a plant pest risk. Triggering an EIS based on the justification 

stated in the Federal Register notice is therefore outside the scope of 

APHIS’ jurisdiction. The U.S. Environmental Protection Agency 

(EPA) has jurisdiction over pesticide use under the Federal 

Insecticide, Fungicide and Rodenticide Act (FIFRA). In addition, a 

recent ruling in the U.S. Court of Appeals for the Ninth Circuit 

(Center for Food Safety v. Vilsack, 9th Cir. May 17, 2013) explicitly 

clarified USDA is not responsible for assessing herbicide use or 

resistance development under the PPA.

Growers need new tools for weed management. With additional 

modes of action, growers will be able to more effectively manage 

Oppose 

preparation of 

EIS

Page 2-32
Comment # Comment ID Commenter Comment Excerpt Topic Area

glyphosate-resistant and conventional weeds. Based upon APHIS’ 

assessment, 2,4-D tolerant corn and soybeans do not pose a plant 

pest risk. Therefore, USDA should immediately convey 

nonregulated status on these traits and make them available to U.S. 

growers.

29 APHIS-2013-

0042-0033

Dallas Peterson -

Kansas State 

University 

Department of 

Agronomy

The ability to effectively control weeds is one of the most important 

factors in profitable crop production. The use of glyphosate in 

Roundup Ready crops was a highly cost-effective approach to weed 

control for many years, but heavy reliance on glyphosate-only weed 

control programs eventually led to the development of glyphosate 

resistant weeds, including marestail, waterhemp, Palmer amaranth, 

kochia and giant ragweed, that are difficult to control with current 

technologies. New technologies such as 2,4-D tolerant crops would 

provide an additional tool that could be incorporated into an integrated 

weed management program to improve overall weed management, 

including glyphosate resistant weeds.

APHIS-2013-

0042-0033

Dallas Peterson -

Kansas State 

University 

Department of 

Agronomy

The introduction of 2,4-D tolerant soybeans would likely increase the 

potential for developing 2,4-D resistant weeds, but I feel the potential 

benefits of helping to control existing herbicide resistant weeds far 

outweighs the risk of developing 2,4-D resistant weeds. I also believe 

the risk of developing 2,4-D resistant weeds if this technology is 

introduced is much lower than what has occurred with glyphosate in 

recent years.

Glyphosate plus 2,4-D is not a viable stand-alone approach to 

successful weed management. Timing is very critical to effective 

control of most weeds with postemergence herbicides. 2,4-D needs to 

be applied to small actively growing weeds for good control. Many 

problematic weeds, especially waterhemp and Palmer amaranth 

germinate over an extended period of time, so later flushes of weeds 

will not be controlled by postmergence herbicides like glyphosate and 

2,4-D. Consequently, weed management will be much more 

successful if postemergence 2,4-D treatments are used in conjunction 

Page 2-33
Comment # Comment ID Commenter Comment Excerpt Topic Area

with preemergence residual herbicides that can provide extended 

control. The use of preemergence herbicides as part of an integrated 

approach has increased in recent years due to the difficulties of 

controlling glyphosate resistant weeds and because of the improved 

commodity prices. Although growers were successful with multiple 

postemergence applications of glyphosate before the development of 

glyphosate resistant weeds, I think farmers now realize the many 

benefits of using a preemergence herbicide in conjunction with a 

postemergence treatment. This approach helps minimize potential for 

early season weed competition and provides more flexibility and better 

efficacy with the postemergence treatment. The other huge benefit is 

that by utilizing more herbicide modes of action, the risk of developing 

herbicide resistant weeds is greatly diminished.

Finally, I believe farmers and crop advisers now realize that relying 

simply on a single technology such as glyphosate in Roundup Ready 

crops is not a sustainable practice and will eventually lead to the 

development of herbicide resistant weeds and the loss of an effective 

tool for weed management. 

30 APHIS-2013-

0042-0034

Cathleen Enright -

Biotechnology 

Industry 

Organization (BIO)

In developing its implementing biotechnology regulations under the 

Federal Plant Pest Act and Plant Quarantine Act, APHIS 

acknowledged that its oversight of the Introduction of genetically 

engineered (GE) plants and other organisms would be In accordance 

with NEPA. The assessment of potential environmental effects has 

always been an important element of the federal regulatory process for 

products of biotechnology whether for plants and other organisms 

under NEPA at APHIS or for pesticides under the Federal Insecticide, 

Fungicide, and Rodenticide Act (FIFRA) at EPA. The basis for the 

APHIS Notices, however, was not any potential environmental impacts 

associated with the plants under review. Rather, the Notices identify 

two issues for consideration In an EIS - the potential selection of 

herbicide resistant weeds and increased herbicide use. As discussed in 

greater detail herein, the law is clear that potential impacts associated 

Oppose 

preparation of 

EIS

Page 2-34
Comment # Comment ID Commenter Comment Excerpt Topic Area

with herbicide use are EPA's responsibility under FIFRA and are 

neither subject to APHIS's jurisdiction under the Plant Protection Act 

(PPA) nor an appropriate basis for preparation of an EIS for an action 

proposed under the PPA.

BIO and its members are also concerned that the decision to prepare 

EISs for the crops identified by APHIS will unnecessarily delay 

Issuance of determinations of nonregulated status, causing significant 

harm to American farmers and the developers of the crops without any 

additional environmental benefit. APHIS's regulations require a 

petition for determination of nonregulated status to either be approved 

in whole or in part or denied within 180 days of the Agency's receipt of 

the completed petition. Yet, the earliest deregulation petition for the 

subject crops was filed with APHIS nearly four years ago and declared 

complete shortly thereafter, and none of the pending petitions for 

which an EIS would be prepared has yet to be resolved. APHIS 

estimates completing the two EISs in the summer of 2014 at the 

earliest, nearly five years after the earliest deregulation petition was 

filed with APHIS and over four years after APHIS's own regulatory 

deadline.

The delay that will result from preparation of the EISs will deny 

American farmers the new tools they need to prevent and combat 

herbicide-resistant weeds and maximize yields. BIO members have 

submitted applications to EPA that would authorize use of their 

herbicides on the associated herbicide tolerant crops identified In the 

APHIS Notices. These herbicides have differing modes of action, 

enhancing the ability of growers to address weed problems and 

supporting the continued use of environmentally sustainable practices 

such as no-till farming.

Delays inherent in the EIS process will also put U.S. corn, soybean 

and cotton growers at a particular disadvantage in relation to their 

counterparts in other nations that are now completing their review 

processes for GE crops on a far more timely basis than the United 

Page 2-35
Comment # Comment ID Commenter Comment Excerpt Topic Area

States. In addition, the developers of these crops will suffer further 

delay in commercializing and offering valuable new products for 

sale and other developers of Innovative products may reconsider 

whether to Invest in the U.S. market. Because the APHIS Notices 

failed to provide a satisfactory legal or scientific justification for 

opting to prepare an EIS for the subject products, developers of 

future products also lack predictability as to whether APHIS will opt 

to prepare an EA or an EIS, which Significantly affects the 

deregulation timeline and product development decisions.

31 APHIS-2013-

0042-0035

- Agricultural 

Retailers 

Association 

- American 

Farm Bureau 

Federation 

- American Seed 

Trade 

Association 

- American 

Soybean 

Association 

- American 

Sugarbeet 

Growers 

Association 

- Biotechnology 

Industry 

Organization 

- National 

Association of 

Wheat 

Growers 

Our members, who produce the vast majority of commodity crops in 

America, must be able to utilize the very best available methods to 

combat weed resistance problems. Weed resistance is a well 

understood scientific phenomenon that is not unique to 

biotechnology or any other form of agriculture. Different herbicides 

attack weeds by different methods or “modes of action.” The delay 

that will result from preparation of the EISs as proposed by APHIS 

will deny growers the tools they need to prevent and combat weed 

resistance and maximize yields through the use of herbicides that 

have been shown to operate with differing modes of action. The 

proposed use of these herbicides in conjunction with the associated 

herbicide tolerant plants also supports the continued use of 

environmentally sustainable practices such as no-till and low-till 

farming.

Additionally, the delays inherent in the EIS process proposed by 

APHIS will put American growers at a further disadvantage to corn, 

soybean and cotton growers in other nations that are now 

completing their review processes for biotechnology-derived crops 

on a far more timely basis than the United States. Any further delay 

is unacceptable, particularly when APHIS’s own regulations require 

APHIS to respond to a petition for determination of nonregulated 

status within 180 days of the Agency’s receipt of the petition. 7 

C.F.R. § 340.6(d)(3).

Oppose 

preparation of 

EIS

Page 2-36
Comment # Comment ID Commenter Comment Excerpt Topic Area

- National Corn 

Growers 

Association 

- National 

Cotton Council

Our members support a science-based, federal environmental review 

process for new agricultural biotechnology products. The Notices of 

Intent issued by APHIS, however, identify two issues for 

consideration in an EIS (i.e., weed resistance and increased 

herbicide use), both of which are subject to the sole jurisdiction of 

the U.S. Environmental Protection Agency (“EPA”) under the 

Federal Insecticide, Fungicide, and Rodenticide Act (“FIFRA”). 

These pesticide issues are unequivocally not subject to APHIS’s 

jurisdiction under the Plant Protection Act.

32 APHIS-2013-

0042-0036

Dow Agrosciences, 

LLC (DAS)

DAS supports a science-based, federal environmental review process 

for those products. That process must of necessity recognize that the 

crops and herbicides are subject to the jurisdiction of two different 

regulatory agencies operating under their own independent statutory 

mandates and differing environmental review standards. DAS is 

concerned that APHIS's planned preparation of an EIS for the 

determinations of nonregulated status requested by DAS for its 

herbicide tolerant crops fails to recognize these distinctions.

Moreover, the EIS preparation process contemplated by APHIS will 

unnecessarily delay issuance of determinations of nonregulated status 

(deregulation) for these crops resulting in irreparable harm to farmers 

and DAS with no additional benefit to the environment. Indeed, delays 

inherent in the EIS preparation process will likely force many com and 

soybean growers to use less sustainable weed management practices 

resulting in soil runoff and other adverse environmental effects. Most 

significantly, these delays will deny growers the new tools they need to 

combat weeds and maximize yields.

Weed resistance is a well understood scientific phenomenon that 

farmers must manage. 1 It is not unique to biotechnology or any other 

form of agriculture. Different herbicides attack weeds by different 

methods or "modes of action." Reliance on a single herbicide and its 

unique mode of action is certainly a contributor to development of 

weed resistance. The applications submitted to EPA by DAS and other 

Oppose 

preparation of 

EIS

Page 2-37
Comment # Comment ID Commenter Comment Excerpt Topic Area

companies for use of their herbicides with the associated herbicide 

tolerant crops are intentionally designed to provide growers with 

herbicides that act by different modes of action, significantly 

enhancing growers' ability to address weed problems, increase yields 

and maintain environmentally preferable, no-till and low-till 

agricultural practices.

Delays inherent in the EIS process will also place U.S. growers at a 

further disadvantage to com, soybean and cotton growers in other 

nations that are now completing their regulatory reviews for 

biotechnology-derived crops on a far more expedited basis than the 

United States. Finally, the decision to prepare a EIS will also be costly 

to DAS, forcing the company to continue producing seed under the 

burdensome APHIS permitting process, in addition to suffering a 

further delay in commercializing and offering its new herbicide 

tolerant crops for sale. For all of these reasons DAS objects to the 

preparation of an EIS for deregulation of its crops.

33 APHIS-2013-

0042-0037

Rachel Lattimore, 

Senior Vice 

President, General 

Counsel, Secretary -

CropLife America

On May 16,2013, APHIS published in the Federal Register notices 

announcing its intention to conduct Environmental Impact 

Statements (EISs) related to several new technologies: dicamba 

tolerant soybeans, dicamba tolerant cotton, 2,4-D tolerant corn, and 

2,4-D tolerant soybeans.1 APHIS's declared intent to conduct these 

EISs focuses solely on pesticide issues regulated by the United 

States Environmental Protection Agency (EPA). We strongly urge 

you to reconsider the need for EISs for these technologies due to

clear limitations on APHIS's Congressional mandate and in light of 

a recent ruling by the Ninth Circuit Court of Appeals clarifying EPA 

and APHIS's respective jurisdictions in this area.2 The proposed 

EISs would introduce unnecessary regulatory redundancy and 

potential regulatory confusion by analyzing the proposed use of 

herbicides that are under active review by EPA and outside the 

jurisdictional purview of APHIS.

Congress's well-established distribution of regulatory authority over 

Oppose 

preparation of 

EIS

Page 2-38
Comment # Comment ID Commenter Comment Excerpt Topic Area

agricultural technologies and recent Ninth Circuit case law establish 

that APHIS's proposed EISs are unnecessary, redundant, and 

potentially in conflict with EPA's authority. In light of these concerns 

and the substantial cost and delay that would be incurred due to such a 

review, CropLife America strongly urges APHIS to reconsider its 

decision to conduct these EISs.

34 APHIS-2013-

0042-0038

Steve Smith,

Chairman - Save 

Our Crops Coalition

We urge the granting of approval for the Dow 2,4 D EnlistTM system 

but maintain grave concerns (as addressed in comments specifically 

on the dicamba petition) about the widespread use of dicamba on the 

environment, which prompted our original petition. Monsanto 

continues to promote practices that will be of great environmental 

risk if widespread use of dicamba is approved without the 

reasonable restrictions that Dow recognized and implemented.

Support approval 

of Dow petitions

35 APHIS-2013-

0042-0039

Joyce Dillard We request that more thorough studies occur on bees and colony 

collapse, birds and the watershed ecosystems as well as viruses that 

spread through migration related to watershed ecosystem connectivity.

Water contamination is a problem in a watershed not necessarily in the 

vicinity of the crops, so all avenues need to be studied.

The liabilities of the Clean Water Act should not be placed on other 

watershed systems.

Herbicide use

36 APHIS-2013-

0042-0040

Lee Van Wychen, 

Director Science 

Policy - WSSA

Science has clearly shown that there is a risk of resistance development 

to all herbicides, and 2,4-D and dicamba are no exception. In fact 

weeds have evolved resistance to nearly all forms of weed control 

including herbicides, tillage, mowing and hand weeding. Some of our 

members have voiced concerns that growers may adopt 2,4-D and 

dicamba technologies and rely too heavily on these herbicides thereby 

developing an even greater weed resistance situation. However, the 

majority of our member scientists view 2,4-D and dicamba resistant 

crops as an additional weed management tool to include in an 

integrated weed management program. The greatest risk for developing 

herbicide resistance is actually occurring right now with the PPO 

herbicides and glufosinate. These products are being over-used in 

Page 2-39
Comment # Comment ID Commenter Comment Excerpt Topic Area

certain cropping systems as farmers have no other effective herbicide 

options. The 2,4-D and dicamba resistant crops could be used to delay 

resistance development to the PPO herbicides and glufosinate and, in 

turn, weed management systems could be developed using the PPO 

herbicides, glufosinate, 2,4-D and dicamba, extending the life of each 

of these chemistries.

APHIS-2013-

0042-0040

Lee Van Wychen, 

Director Science 

Polidy - WSSA

Weed management is ultimately the responsibility of farmers and farm 

advisors. However, the weed science community, including industry, 

academics, crop commodity groups and others who reach out to 

farmers, must recommend robust and effective stewardship programs 

espousing the basic principles of good weed management and 

encourage adoption of these practices. By doing so, evolution of 

resistance to our herbicide resources and new options such as 2,4-D 

and dicamba resistant crops will be minimized.

APHIS-2013-

0042-0040

Lee Van Wychen, 

Director Science 

Polidy - WSSA

Research indicates that 2,4-D and dicamba will fit best in a fully 

diversified program and such a program is particularly important when 

glyphosate resistant palmer pigweed and waterhemp are the targets.

APHIS-2013-

0042-0040

Lee Van Wychen, 

Director Science 

Polidy - WSSA

Resistance to 2,4-D and dicamba represents no more a threat to 

agricultural production than resistance to other critical herbicides and 

the likelihood that it will be used in a manner consistent with best 

management practices is good. 

APHIS-2013-

0042-0040

Lee Van Wychen, 

Director Science 

Polidy - WSSA

Stacking 2,4-D and dicamba tolerance with that of glyphosate, 

glufosinate, and other herbicide tolerant traits will further facilitate the 

use of these herbicides in a diversified program. Stacking herbicide 

traits does not in itself promote the evolution of resistance to more than 

one herbicide since, just as for individual herbicides, the evolution of 

resistance is a function of how the herbicides are used rather than a 

function of the selectivity of the crop to multiple herbicides.

APHIS-2013-

0042-0040

Lee Van Wychen, 

Director Science 

Polidy - WSSA

The ability of farmers to use 2,4-D and dicamba in diversified weed 

management programs in soybeans, corn, and cotton is not expected to 

significantly change current farming practices. These herbicide tolerant 

crops will, however, provide valuable new postemergence options that 

Page 2-40
Comment # Comment ID Commenter Comment Excerpt Topic Area

will allow farmers to most effectively manage their weeds when 

practicing conservation tillage even in the presence of glyphosate 

resistant populations. Farmers have clearly shown a preference for 

postemergence weed control in conservation tillage systems and 2,4-D 

and dicamba can be an important part of this system. 

As the spread of glyphosate-resistant weeds occurred, the adoption of 

tillage, including deep tillage with a moldboard plow has once again 

become more common. The return of conventional tillage has led to 

increased wind and water erosion. Neither 2,4-D nor dicamba 

technologies would eliminate tillage, but they would greatly reduce the 

need for deep tillage allowing many farmers to return to more reduced 

tillage production systems.

APHIS-2013-

0042-0040

Lee Van Wychen, 

Director Science 

Polidy - WSSA

New and expanded uses of existing herbicides are needed for 

integrated weed management programs in order to mitigate weed 

resistance and meet our current and future crop production needs.

APHIS-2013-

0042-0040

Lee Van Wychen, 

Director Science 

Polidy - WSSA

Off target movement of 2,4-D and dicamba pose the greatest limitation 

to the adoption of either auxin technology. An enormous amount of 

research by the registrants and other weed scientists around the world 

has been conducted to develop methods to minimize the potential for 

off-target movement. These efforts include 1) improving herbicide 

formulations, thereby reducing volatility and/or drift, 2) improving 

application equipment techniques and application methods, thereby 

reducing drift, and 3) developing educational materials to assist 

growers in reducing off target movement when making pesticide 

applications. There is no question these research efforts will greatly 

minimize off-target movement of all pesticides, not just 2,4-D and 

dicamba, and will greatly improve the ability of a grower to apply 

pesticides that stay in the targeted area.

Herbicide use -

drift

37 APHIS-2013-

0042-0041

Kenneth Isley, Vice 

President, General 

Counsel, Secretary -

Dow AgroSciences LLC ("DAS") respectfully submits this petition to 

the United States Department of Agriculture ("USDA"), Animal and 

Plant Health Inspection Service ("APHIS"), amending and requesting 

Page 2-41
Comment # Comment ID Commenter Comment Excerpt Topic Area

Dow Agrosciences, 

LLC (DAS)

that APHIS immediately grant DAS's pending petitions for 

determination of nonregulated status for DAS-40278-9 Corn (Petition 

No. 09-233-01 p), DAS-68416-4 Soybean (Petition No. 09-349-0lp), 

and DAS-44406-6 Soybean (Petition No. 11-234-01 P ) (collectively, 

the ''EnlistTM Plants"). See 7 C.F.R. § 340.6(a).

Under the unique circumstances presented here, DAS respectfully 

requests that APHIS:

• immediately grant DAS's pending petitions for determination of 

nonregulated status for the EnlistTM Plants; and

• immediately reconsider and withdraw its decision to prepare an EIS 

as to the EnlistTM Plants and terminate the NEPA process.

APHIS's unwarranted delay in the issuance of determinations of 

nonregulated status for the EnlistTM Plants has caused and will 

continue to cause significant harm to American farmers and DAS. This 

harm will be especially acute, and irreparable, in the event that 

determinations of

nonregulated status are not issued before the fall 2013 harvest. Thus, 

DAS respectfully requests that APHIS respond to this petition within 

the next thirty (30) days, by July 18, 2013.

38 APHIS-2013-

0042-0042

Center for Food 

Safety

Copy of comments submitted to USDA-APHIS under Docket No 

APHIS‐2012‐0019 (DAS 68416-4 soybean) – Comments to USDA 

APHIS on Draft Environmental Assessment and Draft Plant Pest Risk 

Assessment for Dow AgroSciences Petition (09-349-01p) for 

Determination of Nonregulated Status of Event DAS-68416-4: 2,4-D -

and glufosinate-resistant soybean

Attachment APHIS-2013-

0042-0043

Center for Food 

Safety

Copy of comments submitted to U.S. EPA - Comments to EPA on 

Notice of Receipt of Applications to Register New Uses of 2,4-D on

EnlistTM AAD-1 Corn and Soybean

39 APHIS-2013-

0042-0044

Center for Food 

Safety

Copy of comments submitted to USDA-APHIS under Docket No 

APHIS‐2012‐0103 (DAS-40278-9 corn) 

40 APHIS-2013-

0042-0045

Center for Food 

Safety

2,4-D-resistant crops must be viewed as weed control systems 

In preparing the EIS, APHIS must assess 2,4-D-resistant corn and 

Page 2-42
Comment # Comment ID Commenter Comment Excerpt Topic Area

soybeans as crop systems comprising the herbicide-resistant crop 

itself and associated use of 2,4-D. Monsanto describes its Roundup 

Ready (RR) crops as RR crop systems. Dow describes 2,4-Dresistant crops as the “EnlistTM weed control system.” “System” is 

defined as “a set or arrangement of things so related or connected as 

to form a unity or organic whole,”1 meaning there is no need for 

elements not encompassed by the system to accomplish its purpose. 

Exclusive or near-exclusive use of glyphosate as the sole weed 

control measure with Roundup Ready crop systems is a major factor 

in the epidemic of glyphosate-resistant in U.S. agriculture. A similar 

dynamic will be in play with 2,4-D-resistant crop systems, so they 

must be assessed as systems.

APHIS-2013-

0042-0045

Center for Food 

Safety

Impacts of 2,4-D-resistant crop systems on herbicide use

For all practical purposes, 2,4-D-resistant corn and soybeans eliminate 

the severe biological constraints on use of this herbicide with all other 

types of corn and soybeans ever developed or grown. Label rates of 

2,4-D coincide roughly with rates that begin to cause crop damage, and 

the imperative to avoid crop damage is as or more effective than the 

label in keeping 2,4-D use within bounds. Once the crop injury 

constraint is lifted, there is no biological reason for the farmer to 

follow the label. From a modestly used pre- ‐emergence herbicide in 

soybeans and early POST herbicide in corn, 2,4-D will become one of 

the major herbicides for weed control in EnlistTM crop systems (likely 

with additional use of glyphosate, ACCase inhibitors and/or 

glufosinate if stacked with resistance to these herbicides). APHIS must 

assess the shift in 2,4-D use patterns to be expected in various crop 

adoption scenarios. APHIS should assess both the change in amount 

applied, per acre per crop, and the shift in use pattern (i.e. amount used 

pre-emergence vs. post-emergence). APHIS should also assess the 

impact of 2,4-D crops on overall herbicide use, keeping in mind that 

2,4-D would likely displace little if any glyphosate, which has a 

broader spectrum of activity, including (unlike 2,4-D) activity on grass 

Page 2-43
Comment # Comment ID Commenter Comment Excerpt Topic Area

family weeds. We refer APHIS to our comments, where CFS makes 

such projections.

APHIS-2013-

0042-0045

Center for Food 

Safety

Features of HR crop systems that promote HR weeds 

As discussed in our comments, HR crop systems promote not only 

(near-) exclusive reliance on the associated herbicide(s), but also more 

frequent use over a broader application window that extends much 

further into the crop season than would otherwise be possible. 

Resistant weeds with Roundup Ready crops are too often treated 

superficially as simply the result of excessive glyphosate use, but as 

Paul Neve has pointed out, the post-emergence use pattern of 

glyphosate with RR crops is another, independent factor promoting 

weed resistance, beyond exclusivity and frequency of glyphosate use. 

In other words, the timing as well as the exclusivity and frequency of 

herbicide use is a factor in promoting weed resistance. In practice, 

applications are often made late post-emergence to larger weeds, 

increasing resistance risks still more. Additional evidence comes from 

weed resistance to ALS inhibitor herbicides, many of which were and 

are used post-emergence. ALS inhibitor-resistant weeds arose in 1987 

just five years after the first ALS inhibitor herbicide was introduced, 

and became extremely prevalent in less than a decade; in fact, by 

undermining the efficacy of widely used ALS inhibitors (especially in 

soybeans), resistant weeds provided much of the impetus for adoption 

of RR crops (as a means to kill ALS inhibitor-resistant weeds), just as 

glyphosate-resistant weeds have become the rationale for 2,4-Dresistant crop systems. We emphasize that while a post-emergence 

herbicide use pattern is certainly not a necessary condition for weed 

resistance to evolve (e.g. atrazine used primarily pre-emergence and 

early post-emergence in corn led to substantial weed resistance), it 

does appear to be a facilitating factor where present. APHIS must 

assess the post-emergence weed control paradigm that is a central 

feature of HR crop systems for its resistance-promoting potential in the 

case of 2,4-D-resistant crops and weeds, in addition to the more 

Page 2-44
Comment # Comment ID Commenter Comment Excerpt Topic Area

obvious factors of exclusivity and frequency of use.

APHIS-2013-

0042-0045

Center for Food 

Safety

Socioeconomic factors associated with HR crops and HR weeds

As discussed in our comments, pricing strategies influence farmer 

weed management decisions in such a way as to contribute to 

evolution of weed resistance. Companies charge fees for HR traits that 

are substantial enough to create a strong incentive for the farmer to 

make full use of the trait(s) through total reliance on the associated 

herbicide(s). APHIS should find or develop studies that explore the 

extent to which pricing strategies for HR crop systems (e.g. highpriced seed, low-cost herbicide) reinforce herbicide use patterns that 

foster resistance in the case of 2,4-D-resistant corn and soybeans. 

RR crops’ major and closely intertwined “benefits” are reduced labor 

needs for weed management (at least until resistant weeds emerge) and 

the simplicity of glyphosate-only weed control. In addition, 

glyphosate’s superior ability to control large weeds relative to other 

herbicides broadens the application window for acceptable weed 

control. These factors together facilitate increased farm size, since 

more land can be managed for weeds with the same labor, and labor 

needs for weed control are a major limiting factor on farm size. One 

can expect 2,4-D- resistant crops to have similar impacts. APHIS 

should assess the socioeconomic consequences of 2,4-D-resistant corn 

and soybeans, in terms of increased land and rental prices from 

increased competition for land, increased average size of farms, and 

accelerated exit of small- to medium-size farmers from agriculture.

APHIS-2013-

0042-0045

Center for Food 

Safety

HR crops and drift damage

HR crop systems entail a pronounced shift in herbicide use to much 

later in the season when neighboring crops have leafed out and are 

more vulnerable to drift damage (from early season herbicide use when 

drift poses much less risk). Glyphosate has become a leading cause of 

drift damage in the era of Roundup Ready crops, despite the fact that it 

is not a volatile or drift-prone herbicide. This is not merely because its 

use has increased so dramatically, but also because its use has shifted 

Page 2-45
Comment # Comment ID Commenter Comment Excerpt Topic Area

heavily to later in the season. 2,4-D is much more volatile than 

glyphosate, and is particularly prone to vapor drift. APHIS must 

comprehensively assess the increased drift damage that would occur 

with various 2,4-D-resistant corn and soybean adoption scenarios, both 

in terms of lost yield and income, broken down by major crop (e.g. 

soybeans, cotton) or crop category (e.g. vegetables). APHIS should 

further assess the extent to which 2,4-D-resistant crop adoption would 

reduce plantings of susceptible crops (e.g. vegetables, grapes) and/or 

shift acreage to 2,4-D- tolerant crops that could withstand drift level 

doses (e.g. corn). In conducting this assessment, APHIS must account 

for the inevitable use of more drift-prone 2,4-D formulations (e.g. 

because likely to be cheaper than the choline salt), and not presume an 

ideal world scenario where only potentially less drift-prone 

formulations are used. 

APHIS-2013-

0042-0045

Center for Food 

Safety

Crop volunteers resistant to 2,4-D, ACCase inhibitors, glyphosate, 

glufosinate, etc. as weeds

RR crop volunteers have been repeatedly noted as problematic weeds, 

particularly corn, but also cotton and soybeans; and particularly where 

RR crops are rotated (see comments). SmartStax corn is even more 

problematic, since glufosinate as well as glyphosate are eliminated as 

control options. APHIS must assess the increased weediness of 

volunteers of corn and soybeans resistant to 2,4-D, ACCase inhibitors, 

glyphosate, and/or glufosinate. Further, since cross-pollination with 

other prospective herbicide-resistant cultivars will be possible (e.g. 

dicamba-resistant corn), APHIS should consider scenarios with 

volunteers that have stacked resistance. The assessment should include 

increased costs of control, increased use of herbicides, increased weed 

resistance risks from a narrowing of herbicidal control options and 

increased reliance on those (few) herbicides still effective.

APHIS-2013-

0042-0045

Center for Food 

Safety

Interplay between HR traits and Bt resistant pests 

2,4-D-resistant corn will be offered mainly in stacks with Bt traits. 

Research described in the 2,4-D comments shows that HR corn 

Page 2-46
Comment # Comment ID Commenter Comment Excerpt Topic Area

volunteers produce lower levels of Bt toxin and thereby promote Bt 

resistance in corn rootworm; the more HR traits in the corn volunteers, 

the less likely they will be managed adequately, and hence the more 

likely they will contribute to Bt resistance. See discussion in 2,4-Dcomments.

APHIS-2013-

0042-0045

Center for Food 

Safety

Cross-resistance between 2,4-D, dicamba and other synthetic auxin 

herbicides

In our comments, we discuss evidence that certain weeds resistant to 

2,4-D (e.g. waterhemp) also exhibit increased tolerance to dicamba; 

and that dicamba-resistant crops have increased tolerance to 

chlorophenoxy herbicides like 2,4-D. In view of their common 

mechanism of action, these findings strongly suggest the potential for 

evolution of cross-resistance in weeds to dicamba and phenoxy 

herbicides. Most weed biotypes resistant to either dicamba or 2,4-D 

have not been tested for resistance to the other. APHIS must assess the 

potential for 2,4-D crop systems to foster resistance, not only to 2,4-D, 

but also to dicamba, and the impacts such cross- resistant weeds 

(against a background of resistance to glyphosate, ALS inhibitors 

and/or other herbicides), would have on weed control in soybeans, corn 

and other crops. Known weed biotypes with resistance to either 2,4-D 

or dicamba should be tested for tolerance to the other, to help establish 

the potential for such cross- resistance.

APHIS-2013-

0042-0045

Center for Food 

Safety

Non-target effects of 2,4-D-resistant crops

Roundup Ready crop systems have dramatically increased use of one 

of the most effective plant-killing compounds ever developed. 

Glyphosate is particularly noted for its efficacy against perennial 

weeds, which most other herbicides have difficulty controlling. 

Glyphosate use with Roundup Ready crops is a major factor in the 

dramatic decline in Monarch butterfly populations over the past two 

decades (see 2,4-D-resistant soybean comments to USDA). Glyphosate 

has decimated milkweed populations in Midwest corn and soybean 

fields; and milkweed in such fields is the major breeding ground for 

Page 2-47
Comment # Comment ID Commenter Comment Excerpt Topic Area

migratory Monarchs that overwinter in Mexico. APHIS must project 

the impact of 2,4-D-resistant corn and soybean systems (with 

additional resistance to glyphosate and/or glufosinate) in further 

reducing populations of milkweed in agricultural fields and thus 

exacerbating the decline in Monarch populations. 

APHIS-2013-

0042-0045

Center for Food 

Safety

Many glyphosate formulations are extremely toxic to various species 

of frogs. Massive glyphosate use accompanying Roundup Ready crops 

has been posited as a likely factor in the global decline of amphibian 

populations. APHIS must assess the impacts of 2,4-D-resistant corn 

and soybean systems (with additional resistance to glyphosate and/or 

glufosinate) on amphibian populations.

APHIS-2013-

0042-0045

Center for Food 

Safety

Impact of HR crop systems on sustainable weed control

Please assess the impact that Roundup Ready crop systems have had 

on efforts to advance adoption of sustainable weed management 

techniques (e.g. crop rotation, cover crops); and based on this analysis, 

similarly project the impacts that 2,4-D-resistant crops (with additional 

resistance to ACCase inhibitors, glyphosate and/or glufosinate) would 

have on the same.

APHIS-2013-

0042-0045

Center for Food 

Safety

Health impacts of increased 2,4-D use with 2,4-D-resistant crop 

systems

Medical scientists have found 2,4-D use associated with increased risk 

of non- Hodgkin’s lymphoma and other adverse human health impacts 

(for discussion see human health section of 2,4-D comments to EPA). 

Dioxins continue to contaminate 2,4-D, and EPA has failed to collect 

comprehensive, independent data on the dioxin content of the many 

2,4-D formulation used by farmers. CFS projects a many-fold increase 

in use of 2,4-D with introduction of either or both 2,4-D crop systems, 

and thus a further increase in exposure to and disease from this toxic 

herbicide. APHIS and EPA must assess the increased incidence of 

disease to be expected with the substantial increase in 2,4-D use 

accompanying introduction of these crop systems.

Human health –

2,4-D use

APHIS-2013- Center for Food 2,4-D-resistant crops and tillage 2,4-D-resistant 

Page 2-48
Comment # Comment ID Commenter Comment Excerpt Topic Area

0042-0045 Safety Roundup Ready crops have not, as popularly imagined, fostered 

increased use of conservation tillage. The major gains in conservation 

tillage adoption came in the 1980s and early 1990s, in consequence of 

1985 and 1990 Farm Bill provisions that tied subsidies to use of soilconserving practices. In fact, adoption of conservation tillage actually 

stagnated in the decade of Roundup Ready crop adoption. Instead, the 

glyphosate-resistant weeds generated by RR crop systems have led to 

increased tillage for weed control and hence greater soil erosion. CFS 

has presented a detailed analysis to support these conclusions in the 

2,4-D-resistant soybean comments. APHIS must assess the potential 

for 2,4-D crop systems to further increase soil erosion through 

increased use of tillage to control the 2,4-D-resistant weeds that will be 

generated by these crop systems. 

weed 

development –

impacts on tillage 

and soil erosion

APHIS-2013-

0042-0045

Center for Food 

Safety

APHIS should also require the applicants to supply information 

necessary for meaningful risk assessments that is not in their petitions, 

or better yet undertake appropriate research to fill in the gaps. For 

example, the following information should be available for review by 

APHIS and the public:

• Proposed herbicide application regime: how much herbicide, 

how often, window of application. 

• Degree of resistance conferred by the transgene in different 

plant parts and stages of development.

• Expression of the transgene in pollen, nectar; levels of 

herbicide residues and metabolites in pollen, nectar. 

• Herbicide residues and metabolites in plant tissues from the 

time of application through post-harvest.

APHIS-2013-

0042-0045

Center for Food 

Safety

APHIS needs to analyze the following areas: 

• Agricultural production impacts, including and not limited to 

burden on organic and non-transgenic agricultural production 

and potential harms to non--‐target crops from the adoption of 

the HR crop system.

• Environmental impacts, including but not limited to:

Page 2-49
Comment # Comment ID Commenter Comment Excerpt Topic Area

- Herbicide use and changes in herbicide use patterns;

- Gene flow from 2,4-D-resistant corn and soybeans to 

compatible varieties and the resulting increased weediness;

- Agricultural practices, including herbicide use, effects on 

tillage; and

- Weed resistance and volunteers.

• Socioeconomic impacts, such as:

- Transgenic contamination and their effects on both domestic 

and export markets, as well as, consumers and farmers’ right of 

choice 

- Changes in seed industry market concentration and their 

impacts, 

- Effects on the methods and costs of weed control

• Human health impacts, such as:

- Herbicide use, including impacts on farm workers; and

- Safety of food products 

• Livestock health, such as: 

- Herbicide use; and

- Safety of animal feed.

• Threatened and endangered species, such as:

- Herbicide use; and

- Quality of crop tissues as food sources.

• Disease and pest impacts stemming from 2,4-D-resistant 

soybeans and corn and the associated herbicide use.

41 APHIS-2013-

0042-0046

Center for Food 

Safety

Comments to USDA APHIS on Environmental Assessment for the 

Determination of Nonregulated Status of Herbicide‐Tolerant DAS‐

40278-9 Corn, Zea mays, Event DAS‐40278‐9 - Center for Food 

Safety, Science Comments II

See Comment Summary for DEA for DAS-40278-9 Corn

Attachment APHIS-2013-

0042-0047

Center for Food 

Safety

Comments to USDA APHIS on Draft Environmental Assessment and 

Draft Plant Pest Risk Assessment for Dupont-Pioneer’s Petition (11-

Page 2-50
Comment # Comment ID Commenter Comment Excerpt Topic Area

244-01p) for Determination of Nonregulated Status of Insect-Resistant 

and Herbicide-Resistant Pioneer 4414 Maize: Event DP-004114-3

Page 2-51
Table 2-2. Public Scoping Comments Submitted During Virtual Public Meeting

Commenter Affiliation Concern/Issue

June 26, 2013

Ray Gaesser grower and First 

Vice President of 

the American 

Soybean 

Association

They [2,4-D and dicamba] will allow us, on our farm at 

least, to continue to no till. If we don't have those 

products, we may have to go back to tillage to deal 

with some of the weeds that we have.

Agronomic 

practices

We use them [2,4-D and dicamba] on our farms. I've 

been farming 25 years now, and I've had experience 

using both of those products in a different formulation 

for all that time. And, really, I've never had any 

problems with it, (static - cell interference) response to 

our own crop or our neighbor's. As the previous 

speaker said, we are tested in Iowa. As is required of 

all of our applicators that come from the co-ops and 

from the industry, are tested, and understand the need 

and the right way to apply herbicides.

Herbicide use

We used to use a lot of those products, and now with 

glyphosate, we use less in order to address the issues of 

weed resistance in particular, and the real need for 

multiple modes of actions. All of our universities are 

saying that we need multiple modes (indiscernible) of 

action to avoid weed resistance. So I would urge you 

to move forward with both of these applications.

Herbicide use

David Shaw Past President, 

Weed Science 

Society of 

America 

(WSSA)

Biotechnology has allowed us to maximize yields in 

economics, to be able to mitigate the potential 

development of herbicide resistance, and to be able to 

effectively gain tremendously with the development of 

conservation tillage practices in the United States. 

N/A

Herbicide resistance has developed substantially over 

the last few years, but is not a new phenomenon. In 

fact, it has been recorded and noted for over 40 years 

now.

Herbicide-resistant 

weeds

Page 2-52
Commenter Affiliation Concern/Issue

One of the primary practices that we scientists 

recommend in managing proactively herbicide 

resistance is the ability to use a wide diversity of 

mechanisms of actions with different herbicides that 

affect plants in different ways. We need more herbicide 

options to be able to manage these and to be able to 

preserve the utility of those that we already have. The 

ability to effectively use dicamba and 2,4-D in soybean 

and cotton will help fill this critical need.

We have seen the development of herbicide resistant 

plants most notably in the last few years with 

glyphosate resistance in (indiscernible) crops. This 

problem has become widespread, in several of our 

major commodities. And dicamba and 2,4-D, also the 

ability to use a different mechanism of action than what 

is currently available in these crops to be able to more 

effectively and proactively mitigate and delay the 

evolution of herbicide resistance.

There are a number of factors that come into play in the 

evolution of herbicide resistant weeds and crops. 

However, we scientists understand that this is a 

function of managing the practices and the herbicides 

that are available for weed management. It is as such 

not a plant biotechnology issue. It is a use of the 

technology and the rotation and a development of an 

overall plan using various management practices that 

have been identified.

Weed management is ultimately the responsibility of 

farmers and farm advisors that requires the entire 

community of weed scientists, industry, academia, crop 

Page 2-53
Commenter Affiliation Concern/Issue

commodity, and others to be able to effectively steward 

herbicide resistance management. By using the 

development of resisted crops that have the tolerance to 

dicamba and 2,4-D, this represents no greater threat 

than the development of any herbicide technology that 

has hurt in the past.

It is also noted that one of the major challenges that we 

have with the development of herbicide resistance is 

the losses that we are now experiencing in conservation 

tillage acres. Dicamba and 2,4-D tolerance will 

certainly allow us to help preserve these valuable gains 

and the preservation of our soils in the United States.

Page 2-54
Appendix 3. Weed Management and Herbicide Use

Page 3-1
Weed Management and Herbicide Use

Weed control programs are important aspects of corn and soybean production intended to 

prevent the establishment of plants other than the intended crop. In crop production systems, 

these plants, identified as weeds, are controlled using a number of tactics to maximize the 

production of food, fiber, and fuel (Green and Martin 1996). The goal of weed management is to 

reduce weed populations, allowing for more efficient use of herbicides and other cultural 

practices to control weeds.

Each field has a finite amount of resources, i.e., light, nutrients, and moisture, available for the 

growth and development of crops. Weeds allowed to compete with crops can ultimately result in 

crop yield loss. Once the critical period of weed control (CPWC) has been reached, if weed 

control is delayed, the yield loss can increase fairly rapidly. Knezevic concluded that delaying 

the time of weed removal after the starting point of CPWC will cost corn and soybean producers 

an average of 2% in yield loss per every leaf stage of delay (Knezevic, Evans et al. 2003). 

According to Iowa State University research, uncontrolled weeds of 3-4 inches in corn at the V-3 

to V-4 growth stage have been shown to decrease yields by about 3 bushels per acre per day 

(Rosenberg 2013).

Weeds species present varying degrees of competitiveness. Table 3-1 shows the potential yield 

losses associated with specific weed species present at two different densities. The impacts to 

yield are based on normal weather conditions and adequate soil moisture and assume that the 

weeds emerged with the crop. Crops under drought conditions or other stresses may have higher 

yield losses. According to the data, at higher densities annual broadleaf weeds impact yields 

more than annual grasses (Ontario Ministry of Agriculture and Food 2009).

Table 3-1. Soybean and Corn Yield Losses Due to Weeds at Known Populations

Weed

Percent Yield Loss (%)

Corn Soybean

(1 plant/m2) (5 plants/m2) (1 plant/m2) (5 plants/m2)

Annual Broadleaves

Giant ragweed 13 36 14 40

Lamb's-quarters 12 35 13 38

Pigweed 11 34 12 36

Cocklebur 6 22 15 41

Ragweed 5 21 10 33

Wild mustard 5 18 5 18

Velvetleaf 4 15 4 15

Lady's thumb 3 13 4 15

Wild buckwheat 2 10 4 15

Eastern black 

nightshade1 2 7 14 40

Annual Grasses

Giant foxtail 2 10 3 12

Page 3-2
Weed

Percent Yield Loss (%)

Corn Soybean

(1 plant/m2) (5 plants/m2) (1 plant/m2) (5 plants/m2)

Proso millet 2 10 3 12

Fall panicum 2 10 2 10

Barnyard grass 2 7 3 12

Green foxtail 2 7 2 8

Yellow foxtail 1 5 1 5

Old witch grass 1 5 1 4

Crabgrass 1 3 1 4

Volunteer corn -- -- 4 15

1 Eastern black nightshade in soybeans reduces its quality.

Note: Crop losses assume that the weeds have emerged with the crop.

Adapted from www.wedpro75.com (Ontario Ministry of Agriculture and Food 2009)

Yield loss information on weeds at different weed and crop growth stage is available through the 

use of the WeedSOFTTM yield loss calculator (see http://weedsoft.unl.edu, click on “toolscalculators”) (Weed Soft 2013).

The degree of yield loss for a crop can be related to:

• Environmental conditions (e.g., temperature, moisture, etc.),

• The distribution of weed species within a given field;

• Weed density; and 

• The timing of weed emergence (i.e., weed height) relative to the crop growth stage

(Knezevic 2007). 

Therefore, weed management programs should not only focus on minimizing weed density and 

yield reductions, they should also include approaches to minimize weed seed banks. Eliminating 

weeds before seed production diminishes contributions to the weed seed bank and provides the 

best assurance for improving future weed management. 

Weed control programs vary by crop, weed problem, geography, and cropping system (e.g. notill, conventional-till, etc.). Many growers use a combination of weed control techniques 

including cultural, mechanical, and chemical. Practices that establish a dense, vigorous crop 

canopy quickly (e.g. higher seeding rates, optimum soil fertility, proper seedbed preparation, 

seeding depth) provide competition to smother weeds. 

The keys components to successful weed management are: 

• Knowing the exact identity of all weeds in the field; 

• Treating (if necessary) while the weeds are small; 

• Tailoring control measures to the type of weed and its size (Linker, Coble et al.). 

Page 3-3
Although weed control typically involves an integrated approach that includes herbicide use, 

crop rotation, weed surveillance, and weed monitoring (Farnham 2001, IPM 2004, IPM 2007, 

Hartzler 2008, University of California 2009), currently, herbicides are the most common and 

efficient tactic to manage weeds within agroecosystems (Gianessi and Reigner 2007). Various 

strategies utilized for weed management are discussed in the following sections.

Chemical Control - Herbicides

Herbicides are chemicals that move into a plant and disrupt vital biological process. Herbicides 

have been the primary tactic used to manage weed communities in corn and soybean since the 

mid-1960s and will continue to be an important feature of row crop weed management for the 

foreseeable future. One study, which examined aggregated data on crop yield losses and 

herbicide use, estimated that even if additional tillage and hand weeding labor replaced the use of 

herbicides, U.S. crop production would decline by 20 percent with a $16 billion loss in value if 

herbicides were not used (Gianessi and Reigner 2007). Herbicide use is not regulated by APHIS 

but rather by EPA under FIFRA and its amendments.

Before selecting a herbicide program, growers should know what weeds are present or expected 

to appear, the soil texture and organic matter content, capabilities and limitations of the various

herbicides, and how to best apply the herbicides (York and Culpepper 2000). Additionally, 

when selecting an herbicide, a grower must consider, among other factors, whether an herbicide 

can be used on the crop (herbicides are registered by EPA for specific uses and crops), potential 

adverse effects on the crop, residual effects that can limit crops that can be grown in rotation, 

effectiveness on expected weeds, and cost. 

To be effective, herbicides must (1) adequately contact plants, (2) be absorbed by plants, (3) 

move within the plants to the site of action without being deactivated, and (4) reach toxic levels 

at the site of action (Penn State Extention 2013).

Herbicides are classified according to their effects on plants as either selective or nonselective.

Selective herbicides will kill weeds without significant damage to desirable plants. Nonselective 

herbicides kill or injure all when applied at an adequate rate (Penn State Extention 2013). 

Herbicide action is either contact or systemic. Contact herbicides kill only plant tissue contacted 

by the chemical. Systemic herbicides are absorbed from the point of application, either the roots 

or foliage, and move within the plant to other plant parts. Systemic herbicides may be effective 

against both annual and perennial weeds, but are particularly effective for control of established 

perennial weeds. However, systemic movement of an herbicide in perennial weeds can vary 

seasonally (NC State University 1998).

Applications of herbicides to a crop or weed are described according to when they are applied:

• Pre-plant (i.e., burndown): applied to soil before the crop is planted. For pre-plant 

incorporated, herbicides are applied to soil and mechanically incorporated into the top 2 

to 3 inches of soil before the crop is planted. In burndown, generally herbicides are used 

in combination such that there is no selectivity. Burndown applications in both corn and 

soybean often incorporate glyphosate, dicamba, and 2,4-D and may include paraquat or 

glufosinate to control weeds prior to planting the crop.

Page 3-4
• Pre-emergence: applied after the crop is planted, but prior to emergence of weeds. Preemergent herbicides are generally not effective after weeds have established. They may 

be used prior to or after crop emergence.

• Post-emergence: applied after the weeds and crop emerges. Early post emergence 

application occurs when the crop has just emerged and the weeds are small. Postemergent herbicides selectively target weeds relative to the crop. The post materials have 

activity when applied to leaves and can be used over the top of crops if the crop is 

resistant to the active ingredient.

Most herbicides used as pre-plant and pre-emergent applications are residuals, herbicides that 

remain active for several weeks and theoretically work continuously after application. These 

types of herbicides are finding increasing use in the management of glyphosate-resistant weeds. 

(See Appendix 4, Herbicide Use Trends, for more details). Examples include acetochlor, 

trifluralin, metolachlor, metolachlor-S, pendimethalin, atrazine and alachlor. These herbicides 

work by controlling weeds before they germinate or emerge. Usually residual herbicides need 

to be activated by water (Hager and McGlamery 1997). In rainfed crops, residual herbicides 

may fail to become activated during drought. When weather complicates the timing of 

herbicide applications with planting, growers may plant and apply the residual herbicide in a 

mix with a foliar applied product (Monsanto 2010). The foliar product controls emerged weeds 

while the residual material controls weeds prior to germination or emergence.

When herbicides are applied, biochemical pathways that control the growth and development of 

plants are interrupted and plant death and injury occurs (Sosnoskie and Hanson, 2013). These 

biochemical pathways control the growth and development of plants; when herbicides are 

applied, these processes are constrained and plant injury and death will occur. Most herbicides 

bind to, and thereby block the action of, a specific enzyme. Herbicides are classified according 

to their mode of action, which is the overall manner in which the herbicide affects a plant at the 

tissue or cellular level. The Weed Science Society of America (WSSA) has classified herbicides 

by group number, based on their mode of action. Brief descriptions of these groups are provided 

(Sosnoskie and Hanson, 2013) :

Group 1: herbicides inhibit the action of acetyl CoA carboxylase (ACCase) needed for 

the synthesis of lipids. Grasses, but not broadleaf weeds, are affected. 

Group 2: herbicides inhibit the action of acetolactate synthase (ALS) needed for the 

synthesis of three amino acids (isoleucine, leucine, and valine).

Group 3: herbicides inhibit cell division (mitosis inhibitors). 

Group 4: herbicides are growth regulators. At low concentrations, they mimic the plant 

growth hormone auxin and are referred to as synthetic auxins. At high 

concentration they produce distinctive symptoms on broadleaf weeds; twisted 

and curled stems, malformed flowers, thickened or stunted roots, and cupped, 

strapped or otherwise deformed leaves. Grasses are usually resistant.

Group 5, 6, and 7: herbicides inhibit photosynthesis leading to a buildup of highly 

reactive free radicals that damage chlorophyll and cell membranes.

Page 3-5
Group 8: herbicides inhibit fatty acid and lipid biosynthesis but not ACCase (

Group 1). 

Group 9: herbicides inhibit the action of the enzyme enolpyruvyl shikimate-3-phosphate 

synthase (EPSPS) needed for the synthesis of three aromatic amino acids 

(tryptophan, phenylalanine, and tyrosine) that are produced through the 

shikimate pathway.

Group 10: herbicides inhibit glutamine synthetase. These herbicides stop the 

conversion of glutamate and ammonia to glutamine which causes ammonia to 

accumulate in the plant, inhibiting photosynthesis and destroying plant cells.

Group 12: herbicides inhibit carotenoid biosynthesis. Lack of carotenoids results in 

destruction of chlorophyll, which is needed for plant photosynthesis.

Group 14: herbicides inhibit protopophyrinogen oxidase (PPO). PPO inhibitors block 

the production of chlorophyll and cause reactive molecules to form in the cell, 

resulting in the destruction of existing chlorophyll molecules, carotenoids and 

cell membranes.

Group 15: herbicides block mitosis by inhibiting the synthesis of very long chain fatty 

acids.

Group 20, 21, 29: herbicides inhibit the synthesis of cellulose needed for the synthesis 

of cell walls.

Group 22: herbicides inhibit photosystem I (PSI) forming reactive molecules that 

destroy lipids, eventually breaking down plant cell membranes.

Group 27: herbicides inhibit 4-hydroxyphenyl-pyruvate-dioxygenase needed for the 

synthesis of carotenoids.

Herbicides with a common chemistry are grouped into “families.” Also, two or more families 

may have the same site of action, and thus can be grouped into “classes.” Table 3-2 provides 

WSSA herbicide groups with information on modes of action, chemical families, and example 

active ingredients and herbicides.

Table 3-2. Herbicide Groups with Example Active Ingredients and Herbicides.

Site of 

Action 

Group 

(WSSA 

Group) Site of Action

Number of 

Resistant 

Weed 

Species in 

U.S. Chemical Family Active Ingredient Herbicide

Lipid 

Synthesis 

Inhibitors

1 ACCase

Inhibitors 

(acetyl CoA 

carboxylase) 

15 Aryloxyphenoxy

propionate 

(“FOPs”)

fenoxaprop Puma

diclofop Hoelon

fluazifop Fusilade

quizalofop Assure II

Cyclohexanedione

(“DIMs”)

clethodim Select

sethoxydim Poast

Phenylpyrazoline

(“DENs”)

pinoxaden Axial XL

Page 3-6
Site of 

Action 

Group 

(WSSA 

Group) Site of Action

Number of 

Resistant 

Weed 

Species in 

U.S. Chemical Family Active Ingredient Herbicide

Amino Acid 

Synthesis 

Inhibitors

2 ALS Inhibitors 

(acetolactate 

synthase)

44 Sulfonylurea

(“SUs”)

chlorimuron Classic

foramsulfuron Option

halosulfuron Permit

iodosulfuron Autumn

nicosulfuron Accent

primisulfuron Beacon

prosulfuron Peak

rimsulfuron Resolve

thifensulfuron Harmony

tribenuron Express

metsulfuron Ally

triasulfuron Amber

chlorsulfuron Glean

sulfofsulfuron Maverick

mesosulfuron Osprey

Imidazolinone

(“IMIs”)

imazamox Beyond

imazaquin Scepter

imazapic Cadre

imazethapyr Pursuit

Triazoloyrmidine flumetsulam Python

chloransulammethylFirstRate

pyroxysulfam PowerFlex

diclosulam Strongarm

Triazolinones thiencarbazone Component 

of Caperno

Pyrimidinyl(thio)

benzoate

pyrithiobac Staple

Sulfonylaminocar

bonyltriazilonones

flucarbazone Everest

propoxycarbazone Olympus

9 EPSP 

Synthase 

Inhibitor

13 glyphosate RoundUp

Growth 

Regulators 

(Synthetic 

Auxins)

4

19

Specific Site 

Unknown

10 Phenoxy 2,4-D

2,4-DB Butyrac

MCPA

Benzoic acid dicamba Banvel

Carboxylic acid chlopyralid Stinger

fluroxypr Starane

picloram Tordon

Auxin 

Transport

0 Semicarbazone diflufenzopyr Component 

of Status

Photosynthesis

Inhibitors

5 Photosynthesis 

II Inhibitors 

(binding sites 

other than 6 

and 7)

24 Triazine prometryn Caparol

atrazine Aatrex

simazine Princep

Triazinone hexazinone Velpar

metribuzin Sencor

Page 3-7
Site of 

Action 

Group 

(WSSA 

Group) Site of Action

Number of 

Resistant 

Weed 

Species in 

U.S. Chemical Family Active Ingredient Herbicide

6

7

Photosynthesis 

II Inhibitors 

(binding sites 

other than 5 

and 7)

1 Nitrile bromoxynil Buctril

Benzodiazole bentazon Basagran

Photosynthesis 

II Inhibitors 

(binding sites 

other than 5 

and 6)

7 Ureas Lorox

Nitrogen 

Metabolism

10 Glutamine 

Synthesis 

Inhibitor

Phosphonic Acid glufosinate Liberty

Pigment 

Inhibitors

13

27

Diterpene 

Synthesis 

Inhibitors

1 Isoxazolidinone clomazone Command

HPPD

Inhibitors

1 Isoxazole isoxaflutole Balance

Pyrazolone topramezone Impact

Triketone mesotrione Callisto

tembotrione Laudis

Cell 

Membrane 

Disruptors

14

27

PPO Inhibitors 2 Diphenylether acifluoron Blazer

fomasefen Reflex

lactofen Cobra

oxyfluorfen Goal

NPhenylphthalamid

e

flumiclorac Resource

flumioxazin Valor

Aryl triazinone sulfentrazone Spartan

carfentrazone Aim

fluthiacet-ethyl Cadet

Photosystem I 

Electron 

Diverter

5 Bipyridium paraquat Gramoxone 

Inteon

diquat Reglone

Seedling Root 

Growth 

Inhibitors

3 Microtubule 

Inhibitors

6 Dinitroaniline ethalfluralin Sonalan

pendamethalin Prowl

trifluralin Treflan

Seedling Shoot 

Growth 

Inhibitors

8

15

Lipid 

Synthesis 

Inhibitors

8 Thiocarbamate butylate Sutan +

EPTC Eradicane

Long-chain 

Fatty Acid 

Inhibitors

1 Chloroacetamide acetochlor Harness

alachlor Intrro

metalochlor Dual

Page 3-8
Site of 

Action 

Group 

(WSSA 

Group) Site of Action

Number of 

Resistant 

Weed 

Species in 

U.S. Chemical Family Active Ingredient Herbicide

dimethanamid Outlook

Oxyacetamide flufanacet Define

Pyrazole pyroxasulfone Zidua

Sources: (Armstrong 2009, Glyphosate Stewardship Working Group 2012).

Mechanical Weed Control – Tillage

Prior to planting, the soil must be stripped of weeds that would otherwise compete with the crop 

for space, water, and nutrients. Tillage is used to prepare a seedbed, address soil compaction, 

incorporate fertilizers and herbicides, manage water movement both within and out of a 

production field, and control weeds (Heatherly, Dorrance et al. 2009). Soil cultivation or tillage 

can be very valuable in many situations and should be considered as an alternate weed control 

practice where appropriate:

• Tillage serves as another way to control weeds and break certain weed patterns

• Tillage reduces complete reliance on herbicides

• Periodic tillage is a reliable cultural practice that also provides the benefits of removing 

trash build-up on the soil surface and levels ruts or rough spots in fields. 

Some form of conservation tillage is utilized by the majority of corn and soybean growers. 

Tillage can supplement chemical control (i.e., herbicides) and, in the case of light weed 

infestations, could provide sufficient control if used alone. Cultivation should be shallow to 

reduce crop root damage and to avoid breaking through any residual herbicide layer and bringing 

up untreated soil and weed seed. Use of tillage is optimized when weeds are small and should 

not be practiced for a week prior or after post-emergence herbicide application (York and 

Culpepper 2000).

Tillage can be a useful weed control method in some situations but may not be appropriate for all 

producers or areas. For example, tillage is not a good practice where soils are susceptible to 

erosion. Also, no-till soybean production is less successful in heavier, cooler soils more typical 

of northern latitudes (Kok, Fjell et al. 1997, NRC 2010). 

Although tillage may control weeds, fuel costs and machine maintenance may represent 

substantial farm expenditures (NRC 2010). This fact and the availability of herbicide technology 

have driven producers to increasingly adopt chemical management strategies. For example, in 

2012, 98 percent of soybean acreage was treated with synthetic herbicides (USDA-NASS 2013).

Cultural Weed Control

The successive planting of different crops on the same land is known as crop rotation. In 

contrast, the planting of the same crop on the same field in successive years is known as 

continuous crop production. Crop rotations are used to optimize soil nutrition and fertility, 

reduce pathogen loads, control volunteers (carry over in successive years), and limit the potential 

for weeds to develop resistance to herbicides (IPM 2004, IPM 2007, USDA-ERS 2010).

Page 3-9
Crop rotation is also a key element of successful weed control as it often reduces the populations 

of weeds that closely mimic the appearance of the young crop or are tolerant to herbicides often 

used in these crops. Crop rotation should be an integral component of a weed management 

program. Crop rotation generally leads to healthier crops that are more competitive with weeds. 

Moreover, certain weeds are more easily or more economically managed in one crop than in 

another. In general, most weeds are more easily managed in corn or soybeans than in other 

agronomic or horticultural crops. Good control in corn can reduce weed problems in rotational 

crops. Additionally, crop rotation allows use of different herbicide chemistries on the same field 

in different years. This can prevent weed population shifts (changes in the species composition), 

avoid selection of herbicide resistant weeds, and help to keep the overall weed population at 

lower levels. 

Since 1991, 75% of corn planted acreage has been in some form of rotation (USDA-ERS 2010). 

Corn can be grown successfully in a conservation tillage system if rotated with other crops such 

as wheat and soybeans, which will reduce some of the problems encountered with conservation 

tillage (IPM 2007). Crops used in rotation with corn vary regionally and include oats, peanut, 

soybean, wheat, rye, and forage (USDA-APHIS 2010). Alternative rotations are an important 

aspect of overall management strategies, and could theoretically reduce the cycle of herbicide 

applications associated with corn/soybean rotations (DAS 2010). However, the impact of these 

rotations does not appear to have been studied in detail.

Consecutive plantings of corn frequently require at-planting or pre-plant pesticide treatments to 

control corn pests and pathogens as well as supplemental fertilizer treatments (IPM 2004, 

Erickson and Lowenberg-DeBoer 2005, Sawyer 2007, Stockton 2007). Corn-to-corn rotations 

also may require a change in tillage practices. Corn-to-corn cultivation may produce 

substantially greater quantities of field residue, requiring additional tillage prior to planting 

(Erickson and Lowenberg-DeBoer 2005). The increased adoption of corn-to-corn rotation, 

mainly in conventional and GE production systems, has been attributed to rising corn demand 

and prices (Hart 2006, Stockton 2007).

Crop rotation is a common practice on U.S. soybean fields, with approximately 95 percent of the 

soybean acreage planted in some form of a crop rotation system since 1991 (USDA-ERS 2011). 

A variety of crops may be rotated with soybean. In terms of acreage however, corn is the most 

commonly rotated crop. In a survey of major corn/soybean production states, corn and soybean 

were alternated on 72 to 80 percent of acreage, other rotations were grown on 16 to 20 percent of 

acreage, and soybean was grown continuously on 5 to 12 percent of acreage between 1996-2002 

(Sandretto and Payne 2006). Other crops that may be rotated with soybean include wheat, 

cotton, rice, sorghum, barley, oats, and dry beans.

The mitigation of pest cycles on an agricultural field is one of the primary benefits of crop 

rotation. The rotation of other crops following soybean production may disrupt pest life cycles 

that are more adapted to soybean field cultivation than other crops (Poole 2004) through the 

creation of a relatively unstable agroecosystem (Weller, Owen et al. 2010). For example, crop 

rotation may encourage the use of alternative herbicides to further control broadleaf weeds in the 

same field in successive years that would not otherwise be used if continuous soybean was 

grown (Gunsolus 2012).

Page 3-10
Planting high-quality, weed-free crop seed is another cultural practice that keeps weed infestations 

low and easier to manage. One of the most effective means of reducing weed competition is to 

establish a highly competitive crop. This is best accomplished by planting good quality seed into 

a well-prepared seedbed with good fertility and soil moisture. Higher seeding rates can help 

establish a competitive crop and for some weed species delaying planting will allow for 

destruction of early flushes of weeds via tillage or non-selective herbicide application.

Integrated Weed Management

To reduce or mitigate against the selective pressures associated with the use of a single weed 

management practice, agronomists have recommended that growers adopt a diverse weed 

management strategy, also known as integrated weed management (IWM) (Norsworthy 2012, 

HRAC 2013). Effective IWM in crops usually involves a combination of cultural, mechanical, 

and chemical methods. Thus, IWM does not exclude any one management technique. IWM 

integrates practices such as crop rotation, cover crops, competitive crop cultivars, the judicious 

use of tillage, and targeted herbicide application to reduce weed populations and selection 

pressures toward the development of herbicide resistant weeds (Mortensen, Egan et al. 2012).

A variety of strategies have been proposed to help farmers deal with glyphosate-resistant weeds 

(Boerboom 1999, Beckie 2006, Sammons, Heering et al. 2007, Frisvold, Hurley et al. 2009). 

Resistance management begins with good agronomic practices, including the implementation of 

IWM to incorporate diverse weed control practices to reduce the frequency of herbicide 

applications and decrease selection pressure for herbicide resistant weed populations 

(Norsworthy 2012). IWM programs that use herbicides from different groups, vary cropping 

systems, rotate crops, and use mechanical as well as chemical weed control methods will prevent 

the selection of herbicide-resistant weed populations (Powles 2008, Green and Owen 2011, 

Sellers, Ferrell et al. 2011, Gunsolus 2012, HRAC 2013).

The Herbicide Resistance Action Committee, an industry-based group, has developed the 

following general principles of weed resistance management:

• Apply integrated weed management practices. Use multiple herbicide sites-of-action 

with overlapping weed spectrums in rotation, sequences, or mixtures;

• Use the full recommended herbicide rate and proper application timing for the hardest 

to control weed species present in the field;

• Scout fields after herbicide application to ensure control has been achieved. Avoid 

allowing weeds to reproduce by seed or to proliferate vegetatively; and 

• Monitor site and clean equipment between sites.

For annual cropping situations, the following recommendations of the Herbicide Resistance 

Action Committee (HRAC 2013) are provided:

• Start with a clean field and control weeds early by using a burndown treatment or 

tillage in combination with a pre-emergence residual herbicide as appropriate;

• Use cultural practices such as cultivation and crop rotation, where appropriate; and

• Use good agronomic principles that enhance crop competitiveness.

Page 3-11
References

Armstrong, J. (2009). Herbicide How-to: Understanding Herbicide Mode of Action, Oklahoma 

Cooperative Extension Service. PSS-2778.

Beckie, H. J. (2006). "Herbicide-resistant weeds: Management tactics and practices." Weed 

Technology 20(3): 793-814.

Boerboom, C. M. (1999). "Nonchemical options for delaying weed resistance to herbicides in 

Midwest cropping system." Weed Technology 13: 636-642.

DAS (2010). Petition for Determination of Nonregulated Status for Herbicide Tolerant DAS68416-4 Soybean. S. K. Mark, Dow AgroSciences.

Erickson, B. and J. Lowenberg-DeBoer (2005). Weighing the Returns of Rotated vs. Continuous 

Corn. West Lafayette, IN, Top Farmer Crop Workshop Newsletter, Purdue University.

Farnham, D. (2001). Corn Planting. Ames, IA, Cooperative Extension Service, Iowa State 

University of Science and Technology: 8.

Frisvold, G. B., T. M. Hurley, et al. (2009). "Adoption of best management practices to control 

weed resistance by corn, cotton, and soybean growers." AgBioForum 12: 370-381.

Gianessi, L. and N. Reigner (2007). "The value of herbicides in U.S. crop production." Weed 

Technology(21): 559-566.

Glyphosate Stewardship Working Group (2012). GWC-3, Corn and Soybean Herbicide 

Chart. Glyphosate, Weeds, and Crop Series.

Green, D. J. and R. J. Martin (1996). "Dealing with Perennial Broadleaf Weeds in Conservation 

Tillage Systems."

Green, J. M. and M. D. Owen (2011). "Herbicide-resistant crops: Utilities and limitations for 

herbicide-resistant weed management." Journal of Agricultural and Food Chemistry 59: 5819-

5829.

Gunsolus, J. (2012). "Weed Control in Soybean." 

from http://appliedweeds.cfans.umn.edu/weedbull/Soybeans.pdf.

Page 3-12
Hager, A. and M. McGlamery (1997). Principles of Postemergence Herbicides. Champaign, IL, 

University of Illinois, Cooperative Extension Service: 3.

Hart, C. (2006) Feeding the Ethanol Boom: Where Will the Corn Come From? Iowa Ag Review

2011, 

Hartzler, B. (2008). "Timeliness Critical to Protect Corn Yields." Retrieved April 5, 2011, 

from http://www.extension.iastate.edu/CropNews/2008/0523BobHartzler.htm.

Heatherly, L., A. Dorrance, et al. (2009). Sustainability of U.S. Soybean Production: 

Conventional, Transgenic, and Organic Production Systems, Council for Agricultural Science 

and Technology.

HRAC (2013). "Herbicide Resistance Action Committee (HRAC): Resistance Management 

Strategies." from http://www.hracglobal.com/.

IPM (2004). Crop Profile for Field Corn in Pennsylvania. University Park, PA, Department of 

Agronomy, Penn State University: 21.

IPM (2007). Crop Profile for Corn in the Northern and Central Plains (KS, NE, ND, and SD),: 

26.

Knezevic, S. (2007) Timing Weed Control in Corn to Get the Most Effect. CropWatch 

Knezevic, S. Z., S. P. Evans, et al. (2003). "Yield Penalty Due to Delayed Weed Control in Corn 

and Soybean." Crop Managment.

Kok, H., D. Fjell, et al. (1997). Seedbed Preparation and Planting Practices-Soybean Production 

Handbook. Manhattan, Kansas State University.

Linker, H., H. Coble, et al. (unknown) Chapter 3 - Scouting for Weeds. Scouting Soybeans in 

North Carolina 

Monsanto (2010). Petition for the Determination of Nonregulated Status for Improved Fatty Acid 

Profile MON 87705 Soybean. G. Rogan. St. Louis, Monsanto Company.

Page 3-13
Mortensen, D. A., J. F. Egan, et al. (2012). "Navigating a Critical Juncture for Sustainable Weed 

Management." Bioscience 62: 75-84.

NC State University (1998). "Postemergence, Non-Selective Herbicides for Landscapes and 

Nurseries ". Retrieved 11/25/2013, from http://www.ces.ncsu.edu/depts/hort/hil/hil-648.html.

Norsworthy, J. K., Ward, S. M., Shaw, D. R., Llewellyn, R. S., Nichols, R. L., Webster, T. M., 

Bradley, K. W., Frisvold, G., Powles, S. B., Burgos, N. R., Witt, W. W., and Barrett, M. (2012). 

"Reducing the Risks of Herbicide Resistance: Best Management Practices and 

Recommendations." Weed Science(Special issue): 31-62.

NRC (2010). The Impact of Genetically Engineered Crops on Farm Sustainability in the United 

States. Washington, DC, National Academies Press.

Ontario Ministry of Agriculture and Food (2009) Chapter 12: Weed Control: Crop Yield Losses 

Due to Weeds. Agronomy Guide for Field Crops - Publication 811 

Penn State Extention (2013). "Herbicides " Introduction to Weeds and Herbicides. 2013, 

from http://extension.psu.edu/pests/weeds/control/introduction-to-weeds-andherbicides/herbicides.

Poole, T. (2004). Crop Rotation, University of Maryland - Maryland Cooperative Extension: 1-4.

Powles, S. B. (2008). "Evolution in action: Glyphosate-resistant weeds threaten world 

crops." Outlooks on Pest Management 12: 256-259.

Rosenberg, M. (2013) Effect Of Weed Competition On Corn iGrow 

Sammons, R. D., D. C. Heering, et al. (2007). "Sustainability and Stewardship of Glyphosate and 

Glyphosate-resistant Crops." Weed Technology 21(2): 347–354.

Sandretto, C. and J. Payne (2006). Soil Management and Conservation, United States 

Department of Agriculture - Economic Research Service.

Sawyer, J. (2007) Nitrogen Fertilization for Corn following Corn. 

Sellers, B. A., J. A. Ferrell, et al. (2011) Herbicide Resistant Weeds. 2011, 

Page 3-14
Sosnoskie, L. M. and B. Hanson (2013, March 1, 2013). "Understanding herbicide mechanisms 

(modes) of action and how they apply to resistance management in orchards and vineyards." 

Retrieved 11/25/2013, 2013, 

from http://ceventura.ucdavis.edu/?blogtag=mode%20of%20action&blogasset=19305#.

Stockton, M. (2007). "Continuous Corn or a Corn/Soybean Rotation?". Retrieved April 19, 2011, 

from http://liferaydemo.unl.edu/web/cropwatch/archive?articleId=.ARCHIVES.2007.CROP4.C

ROPCOMPARISON_WORKSHEET.HTM.

University of California (2009). UC IPM Pest Management Guidelines: Corn. Oakland, CA, 

University of California Agriculture and Natural Resources, UC Statewide Integrated Pest 

Management Program: 42.

USDA-APHIS (2010). Plant Pest Risk Assessment for DAS-40278-9 Corn. Riverdale, MD, US 

Department of Agriculture, Animal and Plant Health Inspection Service, Biotechnology 

Regulatory Services.

USDA-ERS (2010, July 1, 2010). "Adoption of Genetically Engineered Crops in the U.S.: Corn 

Varieties." Retrieved April 4, 2011, 

from http://www.ers.usda.gov/Data/BiotechCrops/ExtentofAdoptionTable1.htm.

USDA-ERS (2010). "Conservation Policy: Compliance Provisions for Soil and Wetland 

Conservation." Retrieved December 3, 2010, 

from http://www.ers.usda.gov/Briefing/ConservationPolicy/compliance.htm.

USDA-ERS (2011). Major Uses of Land in the United States, 2007. Economic Information 

Bulletin. C. Nickerson, R. Ebel, A. Borchers and F. Carriazo. USDA-ERS, USDA-ERS. 

Number 89: 67.

USDA-NASS (2013). Field Crop Totals.

Weed Soft (2013). "WeedSOFT Web-based Utility." 

from http://weedsoft.unl.edu/weedsoftapps.htm.

Weller, S., M. Owen, et al. (2010). Managing Glyphosate-resistant Weeds and Populations Shifts 

in Midwestern U.S. Cropping Systems. Glyphosate Resistance in Crops and Weeds. Hoboken, 

NJ, John Wiley & Sons, Inc.: 213-233.

Page 3-15
York, A. C. and A. S. Culpepper (2000). "Weed Management." 

from http://www.ces.ncsu.edu/plymouth/cropsci/cornguide/Chapter8.html.

Page 3-16
Appendix 4. Herbicide Use Trends and Predicted Use on EnlistTM Corn 

and Soybean

Page 4-1
Herbicide Use Trends and Predicted Use on EnlistTM Corn and Soybean

In recent years, herbicide use data has generally not been publicly available. For this analysis, third 

party proprietary data was obtained by DAS and assumed to be “reported correctly”. APHIS used 

this information to identify the major herbicides, herbicide sites of action, and trends in their use on 

soybean and corn for the past twenty years. National usage is reported using the metric treatment 

acres and not pounds of active ingredient used per crop. Pounds of active ingredient per crop over 

emphasizes herbicides that are used at high application rates (such as glyphosate, 2,4-D, and 

chloroacetamides) and underestimates the use of herbicides used at low application rates (such as 

acetolactate synthase (ALS) and acetyl-CoA carboxylase (ACCase) inhibitors). The latter 

herbicides may be used at rates 100 times less than the former. Treatment acres refer to the acres of 

land treated with a particular herbicide summed for each time the land is sprayed. For example, if 

one acre of land is sprayed twice with a particular herbicide, it is counted as two treatment acres 

for that herbicide. This metric gives a better representation of grower reliance for a particular 

herbicide than does pounds of active ingredient.

Corn Herbicide Use Trends

The ten most actively used herbicides used on corn, based on treatment acres and in order of use,

nationwide and regionally in 2011 are shown in Table 4-1 and Table 4-2, respectively. The top 10 

herbicides accounts for greater than 95% of the herbicide use on corn (Rausch, 2013). Atrazine has 

historically been the most widely used herbicide on corn through as late as 2007 and is still widely 

used. In 2007, glyphosate became the most widely used herbicide on corn and its use has continued 

to increase through 2011. In addition, chloroacetamide herbicides are also still widely used 

including acetochlor and metolachlor-S. These two chloroacetamides have largely replaced 

alachlor and metolachlor, which were the predominant chloroacetamides used prior to 1997. 

Synthetic auxins such as 2,4-D and dicamba were also commonly used prior to the adoption of RR 

corn. As glyphosate use increased, synthetic auxin use decreased but both dicamba and 2,4-D are 

now finding increased use in corn as is a third synthetic auxin, clopyralid. Presumably the 

increased use of synthetic auxins is in response to the increasing prevalence of glyphosate tolerant 

and resistant weeds. In addition, the two HPPD type inhibitors, mesotrione and isoxaflutole, are 

finding increased use, as is the ALS inhibitor, flumetsulam. 

Also shown in Table 4-1 are the WSSA group number, chemical family name, and site of action 

for the ten herbicides. These ten widely used corn herbicides represent six herbicide sites of action

(Group 9: EPSPS inhibitors, Group 5: Photosystem II inhibitors, Group 15: very long chain fatty 

acid inhibitors, Group 27: 4-HPPD inhibitors, and Group 4: synthetic auxins). For the regional data 

in Table 4-2, just the active ingredient and group number are shown. 

Table 4-1. Top 10 Nationally Used Herbicides on Corn 

Active 

Ingredient

WSSA 

Group Chemical Family Site of Action

glyphosate 9 Glycine 5-enolpyruvylshikimate-3-phosphate 

synthase

atrazine 5 Triazine Photosystem II

acetochlor 15 Chloroacetamide Very Long Chain Fatty Acids

Page 4-2
Active 

Ingredient

WSSA 

Group Chemical Family Site of Action

metolachlor-S 15 Chloroacetamide Very Long Chain Fatty Acids

mesotrione 27 Callistemones 4-Hydroxyphenyl-pyruvate 

dioxygenase

dicamba 4 Benzoic Acid Synthetic Auxin

2,4-D 4 Phenoxy-carboxylic 

acid Synthetic Auxin

clopyralid 4 Pyridine carboxylic acid Synthetic Auxin

flumetsulam 2 Triazolopyrimidine Acetolactate synthase

isoxaflutole 27 Isoxazole 4-Hydroxyphenyl-pyruvate 

dioxygenase

Source: (DAS, 2013a)

Table 4-2. Top 10 Regionally Used Herbicides on Corn

Heartland (6) N Crescent (6) N Great Plains (6) Prairie Gateway (7) Southeast (7)

AI GN AI GN AI GN AI GN AI GN

glyphosate 9 glyphosate 9 glyphosate 9 glyphosate 9 glyphosate 9

atrazine 5 atrazine 5 atrazine 5 atrazine 5 atrazine 5

acetochlor 15 metolachlor-S 15 acetochlor 15 dicamba 4 metolachlor-S 15

mesotrione 27 mesotrione 27 metolachlor-S 15 2,4-D 4 mesotrione 27

metolachlor-S 15 acetochlor 15 mesotrione 27 metaolachlor-S 15 2,4-D 4

flumetsulam 2 flumetsulam 2 isoxaflutole 27 acetochlor 15 dicamba 4

clopyralid 4 clopyralid 4 dicamba 4 mesotrione 27 rimsulfuron 2

isoxaflutole 27 dicamba 4 2,4-D 4 isoxaflutole 27 simazine 5

2,4-D 4 2,4-D 4 clopyralid 4 difluflenzopyr 19 paraquat 22

thiencarbazonemethyl 2 rimsulfuron 2 flumetsulam 2carfentrazoneethyl 14 nicosulfuron 2

Source: (DAS, 2013a)

Heartland: MN, IA, MO, IL, IN, KY, OH

Northern Crescent: WI, MI, PA, NJ, NY, MA, RI, CT, VT, NH, ME

Northern Great Plains: MT, ND, SD, NE

Prairie Gateway: CO, KS, OK, TX

Southeast: AS, LA, MS, AL, GA, SC, NC, TN, VA, WV, MD, DE

Numbers next to the regions represent number of sites of action in the top ten most frequently used herbicides.

AI: active ingredient

GN: WSSA group number

Regional herbicide use on corn largely mirrors national use. The ten most widely used herbicides 

represent either 6 or 7 sites of action. In all regions glyphosate and atrazine are the two most 

frequently used herbicides. After atrazine, chloroacetamides and then HPPD inhibitors are in most 

frequent use in all regions except the Prairie Gateway. In this region, synthetic auxins, dicamba and 

2,4-D are the most frequently used herbicides after atrazine. There are some differences in the type 

of ALS inhibitor used between regions. The Prairie Gateway and Northern Great Plains seldom 

rely on ALS inhibitors in corn. In the other areas, flumetsulam or rimsulfuron are the most 

Page 4-3
commonly used ALS inhibitors. Both the Prairie Gateway and the Southeast use 7 modes of action 

compared to six in the other regions. In the Prairie Gateway, the seventh site of action is the PPO 

inhibitor, carfentrazone-ethyl, and in the South the 7th site of action is, paraquat, a PSI inhibitor

which is commonly included in burndown applications. 

Trends in Herbicide Use on Corn by Site of Action (SOA)

Although weed resistance may be selected against one herbicide in a group and not another (for 

example lambsquarters biotypes have been selected against the synthetic auxin dicamba but not 

2,4-D (Heap, 2011)), there are examples where selection against one herbicide in the Group also 

cross selects resistance to other herbicides of that Group. For example, a biotype selected against 

the Group 2 herbicide imazethapyr was cross resistant to several other Group 2 herbicides 

including imazapic, chlorimuron, pyrithiobac, and flumetsulam (Heap, 2011). From the standpoint 

of managing weed resistance, it is better to rotate herbicide sites of action rather than herbicides 

within a site of action. Because selection of herbicide resistant weeds is a prominent issue in this 

EIS, the analysis of herbicide use focuses on sites of action rather than individual herbicides. 

Figure 4-1 shows the trends in use of herbicide sites of action on corn nationally and by region in 

five year increments since 1990 and in 2011. Group 9 (glyphosate) use on corn has been increasing 

in all regions of the country while there appear to be decreases in the use of Group 15 

(chloroacetamides), Group 2 (ALS inhibitors), and Group 5 (largely atrazine) herbicides. There 

have been increases in Group 4 (auxin) herbicide use regionally in the Southeast and Prairie 

Gateway. 

Page 4-4
Source: (DAS, 2013d).

Classification of herbicides according to site of 

action.: http://www.hracglobal.com/Publications/ClassificationofHerbicideSiteofAction.aspx

Classification of Mechanism of Action http://wssa.net/weed/resistance/. 

Figure 4-1. Trends in Herbicide use on corn by SOA. 

SOA 1 2 3 4 5 6 7 8 9

Chemical 

Family ACCase ALS

Mitosis 

Inhib Auxins

PS II 

Inhib-A1

PS II 

Inhib-B

PS II 

Inhib-A2

FALB 

Inhib

EPSP 

Inhib

SOA 10 13 14 15 16 19 22 27 Other

Chemical 

Family GS Inhib DOXP Inhib

PPO 

Inhib

VLCFA 

Inhib Unknown ATI PS I Inhib HPPD Inhib

US

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

2 3 4 5 6 8 9 15 16 27 OTHER

Heartland

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

2 4 5 6 8 9 15 16 Other 27

Northern Crescent

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

2 4 5 8 9 15 Other 3 22 27

Northern Plains

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

2 4 5 6 8 9 15 16 Other 3 19 27

Prairie Gateway Southeast

Corn

Page 4-5
Soybean Herbicide Use Trends

The trend in soybean herbicide use changed dramatically with the introduction of Roundup 

ReadyTM (RR) soybeans in 1996. The adoption of RR soybeans allowed post emergent application 

of a systemic herbicide (glyphosate) that controlled most grasses and broadleaves with one product 

that only required an average of 1.5 applications during the course of a season. This had the added 

benefits of using a single rate across soil types or pH and did not require either mechanical 

incorporation into the soil or rainfall for activation. This proved an attractive option for farmers 

that allowed a simpler solution and also gave a better weed control result in many cases and at less 

cost. The use of glyphosate post emergent on RR soybeans worked very well because soybeans are 

usually planted in narrow rows which provide rapid canopy closure thereby preventing most weeds 

from germinating. The benefit of total post emergent weed control also supported adoption of no 

till practices, saving time and money for the grower while reducing soil erosion. 

In 1995 prior to the introduction of glyphosate-resistant soybean, the most commonly used 

herbicides in soybean were: imazethapyr (44 percent of soybean acres treated), pendimethalin (26 

percent), trifluralin (20 percent), glyphosate (20 percent) (for pre-plant weed control)and 

metolachlor (10%) (USDA-NASS, 1995). By 2001, glyphosate had become the most commonly 

used herbicide in soybean, used on 73 percent of soybean acres, followed by pendimethalin (10 

percent), imazethapyr (9 percent), fomesafen (7 percent), and trifluralin (7 percent) (USDA-NASS, 

2002). Metolachlor no longer was included in the he top 10 most commonly used herbicides on 

soybean. 

In 2006, glyphosate (all forms) continued to be the most commonly used herbicide on soybean; it 

was used on more than 96 percent of soybean acres and that use has largely continued to the 

present (Table 4-3). The next most commonly used herbicide on soybean was 2,4-D (all forms). 

Its use on soybean for pre-plant weed control has been steadily increasing since 2008 and in 2011

it was used on more than 12 percent of soybean acres. 

Table 4-3. Estimated 2,4-D, Glyphosate, and Glufosinate Use in Soybean, 2008-2011

Year

Total 

Soybean 

Acres

2,4-D Glyphosate Glufosinate

(percent 

acres 

treated)

(lbs/acre)

(percent 

acres 

treated)

(lbs/acre)

(percent 

acres 

treated)

(lbs/acre)

2008 74,404,953 7 0.54 96 1.32

2009 77,584,979 10 0.48 94 1.30 0.3 0.46

2010 78,725,007 10 0.53 94 1.38 1.1 0.52

2011 74,835,007 12 0.55 96 1.40 1.3 0.53

2012 75,939,995 NA NA NA NA 3.9 0.51

NA– Not Available

Source: (DAS, 2012c)

Page 4-6
Although glyphosate use on soybean has remained fairly constant, since 2006, there has been a 

trend to use non glyphosate herbicides for both pre- and post-emergent applications, as depicted in 

Figure 4-3. As noted in Table 4-3, glufosinate use has also been increasing as more growers use 

soybean with the LibertyLink® trait. Between 2011 and 2012, glufosinate use increased 3 fold from 

1.3% to 3.9% of acres treated. 

Source: Total acre treatments from (Monsanto, 2012); soybean planted acres from (USDA-NASS, 2002; USDANASS, 2004; USDA-NASS, 2006; USDA-NASS, 2007; USDA-NASS, 2009; USDA-NASS, 2011)

Figure 4-2. Total Acre Treatments per Soybean Planted Acre and Adoption of GE Herbicide 

Resistant Soybeans, 2002-2011

Table 4-4 lists the 10 most frequently used herbicides on soybean in 2011 based on treatment acres 

in the order of their use. The top 10 herbicides account for greater than 95% of the herbicide use on 

soybean (Rausch, 2013). Glyphosate remains the most widely used herbicide though its dominance 

has been steadily declining since 2005. After glyphosate, the nine most frequently used herbicides 

comprise another five sites of action. These include in order of use, Group 14 PPO inhibitors 

(flumioxazin and fomesafen), Group 2 ALS inhibitors (chlorimuron, imazethapyr, thifensulfuron), 

Group 4 synthetic auxins (2,4-D), Group 15 chloroacetamides (metolachlor-S and acetochlor), and 

Group 1ACCase inhibitor (clethodim) herbicides. 

Table 4-4. Top 10 Most Frequently Used Herbicides on Soybean in 2011 (Nationally)

Active Ingredient WSSA 

Class Chemical Family Site of Action

glyphosate 9 glycine EPSP synthase

chlorimuron 2 sulfonylurea Acetolactate synthase

0

10

20

30

40

50

60

70

80

90

100

0

0.5

1

1.5

2

2.5

2002200320042005200620072008200920102011

US Adoption Rate for GE Herbicide Tolerant Soybeans

Total Acre Treatments Per Soybean Planted Acre

PRE non-glyphosate

PRE glyphosate

POST non-glyphosate

POST glyphosate

TOTAL

GE herbicide tolerant

soybean adoption

Page 4-7
Active Ingredient WSSA 

Class Chemical Family Site of Action

flumioxazin 14 N-phenylpthalimide Protoporphyrinogen 

oxidase

2,4-D 4 Phenoxy-carboxylic 

acid Synthetic auxin

Fomesafen 14 Diphenylether Protoporphyrinogen 

oxidase

Imazethyapyr 2 Imidazolinone Acetolactate synthase

Metolachlor-S 15 Chloroacetamide Very long chain fatty 

acids

Clethodim 1 Cyclohexandione AcetylcoA carboxylase

Chloransulammethyl 2 Triazolopyrimidine Acetolactate synthase

Thifensulfuronmethyl 2 Sulfonylurea Acetolactate synthase

Source: (DAS, 2013a)

Regional Use of Herbicides in Soybean by U.S. Cropping Region

Most of U.S. soybean production occurs in the five regions indicated in Table 4-2. Herbicide use 

on soybeans was examined in these five regions and the top 10 herbicides used are listed in Table 

4-5 based on treatment acres in the order of their use. The Heartland region is where most 

soybeans are grown in the U.S. and accounts for half of all soybean herbicide treatments (data not 

shown). Overall, the herbicides used to control weeds in soybean are similar across regions. 

Glyphosate provides the principal basis for weed control in each of the regions with other actives

from Group 2, Group 4, and Group 14 being used to control weeds that are not controlled 

satisfactorily by glyphosate alone.

Some regional differences in herbicide use are as follows: 

• In the Heartland, Northern Crescent, and Northern Great Plains, Group 15 herbicides are 

not widely used while the Group 1 grass herbicides are. 

• The Northern Crescent is the one region where Group 5 Photosystem II inhibitors are 

widely used. The Northern Crescent is less reliant on synthetic auxins and uses a smaller 

variety of PPO inhibitors and a greater variety of ALS inhibitors.

• In the Northern Great Plains and the Prairie Gateway, Group 3 (mitosis inhibitors) 

herbicides are widely used.

• In the Southeast, Group 22 (Photosystem I) and Group 10 (Glufosinate) are widely used.

• Overall, the Heartland, uses the fewest sites of action in the top ten herbicides (5), the 

Southeast the most (7), while the other three regions use (6). 

Page 4-8
Table 4-5. Top Ten Herbicides and WSSA Group Used on Soybean in the 5 Principal 

Growing Regions 

Heartland (5) N Crescent (6) N Great Plains (6) Prairie Gateway (6) Southeast (7)

AI GN AI GN AI GN AI GN AI GN

glyphosate 9 glyphosate 9 glyphosate 9 glyphosate 9 glyphosate 9

chlorimuron 2 chlorimuron 2 imazethyapyr 2 chlorimuron 2 fomesafen 14

flumioxazin 14 imazethyapyr 2 saflufenacil 14 flumioxazin 14 flumioxazin 14

2,4-D 4 flumioxazin 14 2,4-D 4 2,4-D 4 chlorimuron 2

clethodim 1 clethodim 1 clethodim 1 metolachlor-S 15 metolachlor-S 15

sulfentrazone 14 2,4-D 4 flumioxazin 14 fomesafen 14 2,4-D 4

chloransulammethyl 2 metribuzin 5 chlorimuron 2 sulfentrazone 14 paraquat 22

imazethyapyr 2 thifensulfuron 2 pendimethalin 3 thifensulfuron 2 thifensulfuron 2

fomesafen 14

tribenuron 

methyl 2

chloransulammethyl 2 lactofen 14 glufosinate 10

thifensulfuron 2

chloransulammethyl 2Fluthiacetmethyl 14 pendimethalin 3 dicamba 4

Heartland: MN, IA, MO, IL, IN, KY, OH

Northern Crescent: WI, MI, PA, NJ, NY, MA, RI, CT, VT, NH, ME

Northern Great Plains: MT, ND, SD, NE

Prairie Gateway: CO, KS, OK, TX

Southeast: AS, LA, MS, AL, GA, SC, NC, TN, VA, WV, MD, DE

Numbers next to the regions represent number of sites of action in the top ten most frequently used herbicides.

AI: active ingredient

GN: WSSA group number

Source: (DAS, 2013a)

Trends in Herbicide Use on Soybean by Site of Action (SOA)

Figure 4-3 shows trends in herbicides used on soybean from 1990-2010 in five year intervals and 

for 2011 alone, grouped according to Weed Science Society of America (WSSA) chemical 

classification for sites of action (WSSA, 2013). The analysis presents each herbicide site of action 

(SOA) as a percentage of the total treatment area of all actives used in that year. This approach 

allows a consistent comparison of herbicides used given the changes in crop area over time. The 

figure also breaks down usage by region. It illustrates the decreasing reliance of soybean growers 

on glyphosate and the utilization of additional sites of action including PPO inhibitors (Group 14), 

ALS inhibitors (Group 2), chloroacetamides (Group 15), and synthetic auxins (Group 4) (Figure 4-

3).

In all regions there has been a similar increasing trend in the use of non-glyphosate herbicides as 

weed control has slipped in recent years with some weeds developing increased tolerance or 

resistance to glyphosate and Group 2 herbicides. In all the major soybean growing regions, the next 

most widely used herbicide is either a group 2 (chlorimuron and/or imazethapyr) or a Group 14 

(flumioxazin, fomesan, or saflufenacil) herbicide. In all the regions 2,4-D is also widely used. 

There is increasing pre-emergent applications of residual herbicides such as metolachlor-S and 

pendimethalin in the Northern Great Plains, the Prairie Gateway, and the Southeast. These 

Page 4-9
herbicides prevent weeds from germinating over a period of 4-6 weeks and help control glyphosate 

resistant weeds provided there is adequate rain for activation.

In the Southeast, where glyphosate resistant weeds are the most prevalent, there is a decreasing 

trend in glyphosate use and the greatest use of different sites of action among the various regions.

Page 4-10
Figure 4-3. Trends in Herbicide Use on Soybean by SOA

Soybean

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

1 2 3 4 5 6 9 13 14 15 Other

Heartland

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

1 2 3 4 5 6 9 13 14 15 Other

Northern Plains

SOA 1 2 3 4 5 6 7 8 9

Chemical 

Family ACCase ALS

Mitosis 

Inhib Auxins

PS II 

Inhib-A1

PS II 

Inhib-B

PS II 

Inhib-A2

FALB 

Inhib

EPSP 

Inhib

SOA 10 13 14 15 16 19 22 27 Other

Chemical 

Family GS Inhib DOXP Inhib

PPO 

Inhib

VLCFA 

Inhib Unknown ATI PS I Inhib HPPD 

Inhib

Source: (DAS, 2013d)

Classification of herbicides according to site of action. http://www.hracglobal.com/Publications/ClassificationofHerbicideSiteofAction.aspx

Classification of Mechanism of Action http://wssa.net/weed/resistance/

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

1 2 3 4 5 6 9 10 14 15 22 Other

Southeast

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

1 2 3 4 5 6 9 13 14 15 Other

Prairie Gateway

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

1 2 3 4 5 6 7 9 13 14 15 Other

Northern Crescent

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1990 1995 2000 2005 2010 2011

1 2 3 4 5 6 9 14 15 Other

US

Page 4-11
Summary of Herbicide Trends in Soybean

Trends in herbicide use are evident in Figure 4-3. Since the mid-2000s, at the national level, the 

use of glyphosate and microtubule inhibitors has been declining. The use of four other sites of 

action has been increasing. These are the ALS inhibitor, chlorimuron, the PPO inhibitors 

flumioxazin and fomesafen, the auxin 2,4-D and the chloroacetamide, metolachlor-S. The greatest 

decline in glyphosate use has been in the southeast. In all 5 soybean regions, chlorimuron use on 

soybeans appears to be increasing. In the Prairie Gateway and Southeast, 2,4-D and flumioxazin 

use on soybean appears to be increasing. In the Southeast, fomesafen and metolachlor-S use also 

appear to be increasing.

Comparison of Herbicide Use in Corn and Soybean

Herbicide use in corn differs substantially from that in soybean both in the types of herbicides used 

and the variety of herbicide sites of action. Corn yields are more negatively impacted by early 

season weed competition than soybeans. Corn is also planted in wider rows than soybeans and the 

resulting penetration of light allows weed germination over a longer period of time than in 

soybeans (Rausch, 2013). For these reasons, post emergent applications of glyphosate are not as 

beneficial in corn as they are in soybean. To obtain the best corn yields, growers need to manage 

weeds with pre-plant or pre-emergent herbicide applications. Historically they have used atrazine, 

and chloroacetamide herbicides such as acetochlor, metolachlor, and more recently metolachlor-S. 

They also relied on both dicamba and 2,4-D. Even after RR corn was widely adopted, most corn 

growers have continued to use residual herbicides followed by application of post emergent 

herbicides as needed to provide good weed control and maximize yield potential. Consequently, 

soybean growers have been much more reliant on glyphosate than have corn growers.

Figure 4-4 shows the number of herbicidal sites of action (SOA) corn and soybean growers used in 

2005, 2008, and 2011. Whereas 3/4 of soybean growers relied exclusively on a single SOA for 

their weed control in 2005, less than 1⁄4 of corn growers similarly relied on a single SOA. When 

only one SOA is used, in both cases the predominant herbicide is glyphosate (Figure 4-5). For 

soybean growers who used just one SOA, greater than 97% of the growers used exclusively 

glyphosate whereas in corn, this number was 75% in 2005 but increased to 90% in 2011. The 

alternative herbicides that are used as the only SOA on corn include atrazine, glufosinate, HPPD 

inhibitors, or chloroacetamides. However more commonly, several SOAs are used to raise corn. 

Over 30% of corn growers used at least three sites of action and this trend did not change over the 

period of 2005 to 2011 (Figure 4-4). In comparison, over the same period of time soybean growers 

using three sites of action changed from just over 5% to nearly 20%. Soybean growers using only 

glyphosate decreased to just over 65% in 2008 and further decreased to 44% of growers in 2011. 

As in soybean, the recent trend in corn has also been to use even more herbicide SOAs. For 

example from 2005 to 2011, the percentage of growers using 4 SOAs almost doubled from 10% to 

20%. There has also been an upward trend in corn growers using herbicides representing 5 and 6 

SOAs. 

Page 4-12
Source: (DAS, 2013c)

Figure 4-4. Herbicide sites of action used in soybeans and corn since 2005 based on national 

data.

Number of Sites of Action Used/Acre Number of Sites of Action Used/Acre

Trends in SOA in Soybeans

Trends in SOA in Corn

Number of Sites of Action Used/Acre 

Number of Sites of Action Used/Acre 

Page 4-13
Figure 4-5. Herbicides used in Corn and Soybean when a Single Herbicide is Applied.

Source: (DAS, 2013d)

Proportion of Soybean Area Recieving One 

Active in 2011 by Site of Action

9 Glyphosate

2 ALS

Other

Proportion of the Corn Area Recieving One 

Active in 2011 by Site of Action

9 Glyphosate

5 triazines

10 glufosinate

27 isoxaflutole, 

mesotrione

Other

Proportion of Soybeans Recieving 1 SOA in 2008 

by SOA

9 Glyphosate

other

Proportion of Corn Area Recieving 1 SOA in 2008 

by SOA

9 Glyphosate

27 isoxaflutole, 

mesotrione

5 triazines

15 acetamides

other

Proportion of Soybeans Recieving 1 SOA in 2005 

by SOA

9 Glyphosate

other

Proportion of Corn Recieving 1 SOA in 2005 by 

SOA

9 Glyphosate

5 triazines

15 acetamides

27 isoxaflutole, 

mesotrione

10 glufosinate

Soybean receiving 1 SOA Corn receiving 1 SOA

2011 2011

2008 2008

2005 2005

Page 4-14
Trends in Preplant/Pre-emergent vs Post-emergent Herbicide Use in Corn and Soy

As described more fully in Appendix 3, pre-plant herbicide use refers to use of the herbicide prior 

to planting the crop, pre-emergent describes use of the herbicide prior to weed emergence, and 

postemergent describes use after the crop and weeds emerge. Figure 4-6 shows the most commonly 

used herbicides on corn and soybean and the percent each herbicide was used pre-plant/preemergent (pre) or post-emergent (post) in approximately five year increments since 1990 (DAS, 

2013a). In some situations, such as the use of herbicide on perennial crops and fallow, this 

nomenclature is not applicable (NA) and notated accordingly. Herbicides that are primarily used in 

pre-emergent applications include acetachlor, metolachlor, metolachlor-S, atrazine, isoxaflutole, 

pendimethalin trifuralin, and paraquat. Herbicides that are used primarily post emergent include 

fomesafen, imazethapyr, thifensulfuron, glyphosate, and glufosinate. Some herbicides are widely 

used for both preplant/pre-emergent and post-emergent applications including 2,4-D, dicamba, 

flumetsulam, and mesotrione. One noteworthy trend is that for both 2,4-D and dicamba, pre-plant 

uses are increasing while post-emergent uses are declining. Presumably this use reflects increased 

use of these herbicides for pre-plant burndown to better manage glyphosate resistant weeds. 

Page 4-15
0%

20%

40%

60%

80%

100%

NA

POST

PRE

NA

POST

PRE

NA

POST

PRE

NA

POST

PRE

NA

POST

PRE

Flumetsulam Fomesafen Glufosinate Glyphosate Imazethapyr

0%

20%

40%

60%

80%

100%

NA POST PRE NA POST PRE NA POST PRE NA POST PRE

Isoxaflutole Mesotrione Metolachlor Metolachlor-S

0%

20%

40%

60%

80%

100%

NA POST PRE NA POST PRE NA POST PRE NA POST PRE

Pendimethalin Thifensulfuron Trifluralin Paraquat

0%

20%

40%

60%

80%

100%

NA POST PRE NA POST PRE NA POST PRE NA POST PRE

2,4-D Acetachlor Atrazine Dicamba

1990

1995

2000

2005

2011

Figure 4-6. Timing of Herbicide Use. 

For each herbicide, the percentage of that herbicide used either post emergent, pre-emergent, or in situations where the timing is not applicable (NA) is 

noted for the years indicated. 

Source: (DAS, 2013a)

Page 4-16
Common and Unique Herbicides Used in Corn and Soybean

One of the strategies to reduce the pressure of selecting herbicide resistant weeds is to diversify 

the herbicide sites of action that are used. As crops often are managed with different herbicides, 

crop rotation can facilitate the use of different herbicidal sites of action. To compare the extent to 

which herbicide sites of action would vary in a corn-soy rotation, the common and unique 

herbicides were identified from among the most widely used herbicides in the two crops. Sites of 

action corresponding to these herbicides were then compared. This information is presented in 

Table 4-6 for each of the five major corn and soybean regions. If an herbicide is used only on 

soybean in a particular region, the corresponding matrix square is colored blue. If the herbicide is 

only used on corn, the square is colored yellow. If the herbicide is used on both crops, the square 

is colored green. The stippled green squares represent the situation where a common SOA is 

used on both crops but the herbicides used differ. For the most part, Group 14 PPO inhibitors, 

Group 1 ACCase inhbitors, and Group 10 glufosinate herbicides are used on soy. Group 5 PSII 

inhibitors and Group 27 HPPD inhibitors are used on corn. The Group 15 chloroacetamides, 

which historically have been used primarily on corn, are now seeing increased use on soybean 

especially in the Prairie Gateway and the Southeast. Glyphosate and auxins, particularly 2,4-D 

are used on both corn and soybean. The auxins, dicamba and clopyralid, are still mostly used on 

corn. 

Table 4-6. Common and Unique Herbicides Used in Corn and Soy1

Regions Heartland

Northern 

Crescent

Northern

Great 

Plains

Prairie 

Gateway Southeast

Sites of Action WSSA

EPSPS 9 both both both both both

Auxin Action 4 both both both both both

PSI 22 N/A N/A N/A N/A both

ALS 2 soy

PPO 14 soy soy soy soy

ACCase 1 soy soy soy N/A N/A

Microtubule 3 N/A N/A soy soy N/A

GS 10 N/A N/A N/A N/A soy

PSII 5 corn corn corn corn

HPPD 27 corn corn corn corn corn

Chloroacetamide 15 corn corn corn both both 1

based on the 10 most widely used herbicides in a given region: Source: (DAS, 2013a).

Key

Green (both): Herbicides with the same site of action used in both soybean and corn in a given region. 

Green Shaded: Herbicides with the same site of action used in both soybean and corn but differing in 

individual herbicides.

Blue (soy): Herbicides with a site of action used only on soy in a given region.

Yellow (corn): Herbicides with a site of action used only on corn in a given region.

White (N/A): Not applicable because herbicides with that site of action are not used in the region.

Page 4-17
Herbicide Use in the Different Market Segments

Only a few of the major herbicides used in corn and soybean have a major portion of their use in 

non-crop markets. These herbicides are glyphosate, pendimethalin and the synthetic auxins 2,4-

D, clopyralid, and dicamba (Figure 4-7). In addition to use on agricultural crops, these 

herbicides are applied for use on range and pasture use and non-crop uses. 

Figure 4-7. Herbicide Use by Market Segment 

Source: (DAS, 2013a).

Current 2,4-D Use 

The herbicide 2,4-D is a phenoxy auxin herbicide, introduced more than 60 years ago and 

registered and used throughout the world for the treatment of broadleaf weeds. The mode of 

action of 2,4-D is described as an “auxin mimic,” meaning that it kills the target weed by 

mimicking auxin plant growth hormones like indole acetic acid (IAA) (Tu et al., 2001). Auxins 

and synthetic auxinic herbicides regulate virtually every aspect of plant growth and development; 

at low doses, auxinic herbicides possess similar hormonal properties to natural auxin (Kelley and 

Clopyralid Use by Segment

Crop Use

Range & Pasture

Non Ag

Pendimethalin Use by 

Segment 2011

Crop Use

Range &

Pasture

Non Ag

Dicamba Use by Segment 

2011

Crop Use

Range &

Pasture

Non Ag

Glyphosate Use by Segment 2011

Crop Use

Range & Pasture

Non Ag

2011 Use of 2,4-D by Pounds Active

Crops

Range & Pasture

Non-Crop

glyphosate

clopyralid

dicamba

pendimethalin

2,4-D

Page 4-18
Riechers, 2007). However, as rates increase, they can cause various growth abnormalities in 

sensitive dicots (Tu et al., 2001). Observable plant responses to 2,4-D can include epinasty, root 

growth inhibition, meristematic proliferation/callusing, leaf cupping/narrowing, stem cracking, 

adventitious root formation, senescence, and chlorosis. This uncontrolled and disorganized plant 

growth eventually leads to plant death when applied at effective doses (Tu et al., 2001). The 

agricultural segment is made up of the crop use segment and the range and pasture segment. 

Within the crop segment these uses are very diverse ranging from burndown application prior to 

planting soybeans, to use underneath tree crops and use on wheat. The range and pasture 

segment consists of control of annual weeds as well as control of perennial weeds, woody and 

invasive species. Unlike the other herbicides, less than 50% of 2,4-D is used in the crop segment 

(Figure 4-7).

Source: (US-EPA, 2012c).

Figure 4-8. 2,4-D Agricultural Usage by Crop Reporting District, 2006–2010

As can be seen in Figure 4-8, 2,4-D is used predominantly in the Heartland, Prairie Gateway, the 

Southeast, and Northwestern U.S. 2,4-D controls many broadleaf weeds including carpetweed, 

dandelion, cocklebur, horseweed, morning glory, pigweed sp., lambsquarters, ragweed spp., 

shepherd’s-purse, and velvetleaf. It has little to no effective activity on grasses, including wheat, 

corn, and rice (Industry Task Force II, 2005). The states with the highest use in both periods 

from 2001–2005 and 2006–2010 were Texas, Oklahoma, Kansas and Montana, while the sites 

with the highest use in terms of total pounds applied in these periods were pastureland, winter 

wheat, and corn. The three highest use states are those with some of the highest amounts of 

pastureland. The share of 2,4-D use on pastureland declined considerably between 2001–2005 

and 2006–2010. The most non-agricultural usage in terms of pounds applied as reported in 2003 

Page 4-19
and 2005 was by consumers for lawn use, direct application, or as a fertilizer combination (USEPA, 2012b). 

2,4-D is an ingredient in approximately 660 agricultural and home use products as a sole active 

ingredient or in conjunction with other active ingredients. In 2002, 2,4-D was ranked as the third 

most used herbicide by active ingredient in the U.S. for all purposes (~46 million pounds), 

behind glyphosate (~102 million pounds) and atrazine (~77 million pounds) (Gianessi and 

Reigner, 2006). That same report found that the use of 2,4-D remained relatively steady from 

1992 to 2002; Since that time, 2,4-D use has been increasing from about 46 million pounds in 

2002 to 64 million pounds in 2011 (DAS, 2013b). In 2011, about 40% of 2,4-D was used on 

crops, 38% was used on turf and ornamentals, and 22% was used on range and pasture and for 

industrial vegetation management such as to control unwanted vegetative growth on utility 

corridors, rights-of-way, roadsides, railroads, cemeteries, non-crop areas, and managed forest. It 

is also used to control aquatic and nuisance weeds, e.g., purple loosestrife (Industry Task Force 

II, 2005). 2,4-D is very widely used for non-agricultural use. 

A major use today of 2,4-D is in combination with other herbicides because it economically 

enhances the weed control spectrum of many other herbicides such as glyphosate, dicamba, 

mecoprop, and ALS herbicides (US-EPA, 2005). Agriculturally, it is used on a variety of grass 

crops including pasture/hay, small grains (spring wheat, winter wheat, rice, sorghum, barley, 

millet, oats), corn, and sugar cane and on nut and fruit tree crops (almonds, apples, apricots, 

cherries, citrus, hazelnuts, nectarines, peaches, pears, pecans, pistachios, plums, and walnuts). It 

is also used in the production of some crops which are very sensitive to 2,4-D such as soybean, 

cotton, grapes where the 2,4-D is used without applying it to the crop (see Table 4-7). Table 4-7 

lists the crops where at least 10% of the crop is treated with 2,4-D and includes how many 

pounds of 2,4-D were applied based on EPAs screening level usage analysis conducted in 2012

(US-EPA, 2012b). Although 2,4-D is labeled for use in corn as a broad-leaf weed herbicide, its 

use is limited beyond early seedling stages because it can produce significant malformations of 

corn plants when applied at late seedling stages (Wright et al., 2010). When used in soybean 

production, 2,4-D is applied as a pre-plant burndown treatment. 

Page 4-20
Table 4-7. Agricultural Uses of 2,4-D

Amount Used Percent Crop Treated

Crop

Pounds Active 

Ingredient 

(lbs a.i.)

Average Maximum

1 Almonds 200,000 15 20

2 Apples 80,000 20 25

3 Apricots 2,000 10 25

4 Asparagus 5,000 10 30

5 Barley 500,000 25 40

6 Cherries 30,000 15 25

7 Corn 3,200,000 5 10

8 Cotton 700,000 10 15

9 Fallow 2,300,000 25 30

10 Grapefruit 10,000 10 25

11 Grapes 50,000 5 15

12 Hazelnuts (Filberts) 20,000 25 35

13 Nectarines 5,000 15 35

14 Oats 300,000 15 20

15 Oranges 100,000 20 30

16 Pasture 10,600,000 10 15

17 Peaches 30,000 20 30

18 Peanuts 50,000 5 10

19 Pears 10,000 15 20

20 Pecans 40,000 10 15

21 Pistachios 9,000 5 20

22 Plums 5,000 15 30

23 Prunes 20,000 15 25

24 Rice 300,000 10 15

25 Sorghum 900,000 20 30

26 Soybeans 2,900,000 10 15

27 Sugarcane 400,000 40 65

28 Sunflowers + 60,000 5 10

29 Sweet Corn 7,000 5 10

30 Tangelos 1,000 30 45

31 Tangerines 2,000 10 20

32 Walnuts 40,000 10 15

33 Wheat 5,900,000 30 65

 Source: (US-EPA, 2012a).

Page 4-21
The current EPA-approved use directions for 2,4-D on corn allows a single pre-emergent (burn 

down) application of 0.5-1 lb acid equivalents/acre (ae/ac) of 2,4-D, a single post-emergent 

application of 0.5 lbs ae/ac, and a single preharvest application of up to 1.5 lbs ae/ac. Seasonal 

maximum use is 3 lbs ae/ac/season (DAS, 2010a).

The current EPA-approved use directions for 2,4-D on conventional soybean allows a single

pre-plant (burn down) application of 0.35-1 lb acid equivalents/acre (ae/ac) of 2,4-D. There is

a 7 to 30 day pre-plant restriction, depending on the application rate used during the pre-plant

application (DAS, 2010b).

When 2,4-D is utilized in a burn down or pre-plant treatment (corn or soybean), it is almost 

always combined in a tank mix with glyphosate or other non-selective herbicide and, when 

tank-mixed, 2,4-D is generally recommended at the lower end of the rate range ~ 0.5 lbs ae/ac 

(Nice et al., 2013)

In 2012, 97 million acres of corn was planted and 97.4 million acres were planted in 2013 

(USDA-NASS, 2013). Based on third party proprietary data obtained by DAS, in 2011, 5.5 

million pounds of 2,4-D were applied to 9.5 million acres (10% of the corn crop) for an average 

of 0.57 lbs ae/treated acre while in 2009, 4 million pounds were used on 7.3 million acres (8.4% 

of the corn crop) for an average of 0.55 lbs ae/treated acre (Table 4-8) (DAS, 2012d).

Table 4-8. 2,4-D Applied to Corn

Year Total 

Acres

Acres 

treated 

with 2,4-D

Treated 

Acres % of 

Total 

Acres

Total 

Pounds 

2,4-D

Pounds 

2,4-D/

Acre

Total 

Applications

/ Acre

2009 86,382,000 7,300,000 8.4 4,000,000 0.55

2011 91,936,000 9,500,000 10 5,500,000 0.57

Source: (DAS, 2012d).

In 2012, 77 million acres of soybean was planted and 77.7 million acres were planted in 2013. 

2,4-D use as a pre-plant burndown material has continued to increase between 2008 to 2011 

where the percent of the crop treated has increased from 7% to 12% and total pounds used has 

increased from 2.7 million pounds to 4.9 million pounds (Table 4-9) (DAS, 2012c). 

Table 4-9. 2,4-D Applied to Soybean

Year Total 

Acres

Acres 

treated 

with 2,4-D

Treated 

Acres % 

of Total 

Acres

Total 

Pounds

2,4-D

Pounds 

2,4-D/

Acre

Total 

Applications

/Acre

2008 74,404,953 5,068,628 7 2,716,207 0.5 1.01

2009 77,584,979 7,637,880 10 3,680,330 0.4 1.01

2010 78,725,007 7,763,593 10 4,106,140 0.5 1.00

2011 74,835,007 8,832,324 12 4,893,146 0.5 1.00

Source: (DAS, 2012c).

Page 4-22
Current Quizalofop Use

DAS-40278-9 corn is resistant to quizalofop-P-ethyl whereas conventional corn is sensitive. The 

“fop” herbicides (AOPP ACCase inhibitors) have been registered for crop use for more than 20 

years (USDA-APHIS, 2010). The “fop” herbicides traditionally have not been used to control 

weed species in cornfields because, as a grass (Poaceae family) species, corn is damaged by 

AOPP ACCase inhibitor activity. The registration and use of “fop” herbicides has been 

primarily on broadleaf crops, such as soybean, to control grass weed species, although certain 

cereal plant varieties have a level of tolerance to some “fops” (see DuPont, 2010). According to 

the USDA National Agricultural Statistics Service (NASS) Agricultural Chemical Use Database, 

“fop” type herbicides were used for weed control on at least 23 food crop species between 1990 

and 2006, totaling more than 16 million pounds of active ingredient (USDA-NASS, 2011). 

The AOPP herbicides inhibit chloroplastic ACCase, which catalyzes the first committed step in 

fatty acid biosynthesis, causing plant death (Burton et al., 1989). There are three families of 

ACCase inhibitors, the “fops”, the “dims”, and the “dens” where Quizalofpr-ethyl belongs to the 

“fops” family.The herbicidal activity of quizalofop-ethyl ester was first reported in 1983, and 

quizalofop-ethyl was first approved for use in a registered herbicide product in the U.S. in 1988 

(DAS, 2010b; DuPont, 2010).

1

 However, all end use product registrations were cancelled prior 

to 1996 and it was replaced by the more active quizalofop-P-ethyl (pure R-enantiomer of 

quizalofop racemic mixture), which first was approved for use in a registered product in 1990 

(DuPont, 2010). Quizalofop-P-ethyl is a systemic herbicide that is absorbed from the leaf 

surface and translocated throughout the plant (DAS, 2010b). 

Most non-graminaceous plants (dicots and sedges) are tolerant to quizalofop. Dicotyledonous 

plants contain a prokaryotic form of ACCase which is insensitive to “fop” herbicides. In 

contrast, monocotyledonous plants contain a sensitive eukaryotic form of ACCase in the plastid 

(DAS, 2010a). This is the primary reason that the “fop” herbicides are generally good 

graminicides, with little activity on dicot plants. In addition, some grass species, including some 

cereal crops and weeds (e.g., annual bluegrass and wild oats), are tolerant of some of these 

herbicides (i.e., clethodim, quizalofop, and others) due to their ability to metabolize the 

herbicides to inactive forms (Devine and Shukla, 2000; Powles and Preston, 2009). 

Quizalofop-P-ethyl is used as a selective post-emergent herbicide for the control of annual and 

perennial grass weeds in 23 broadleaf food crop species. The currently registered uses of 

quizalofop-p-ethyl include canola, crambe, cotton, crops grown for seed, eucalyptus, dry beans 

(including Chickpea), dry and succulent peas, flaxseed, hybrid poplar plantings, lentils, mint 

(spearmint and peppermint), pineapple, ryegrass grown for seed, snap beans, soybeans, sugar 

beets, sunflowers, and noncrop areas. Current allowable rates for this herbicide vary from 

0.0172 to 0.344 lb ai/acre, depending on crop and weed conditions (see EPA approved label for 

Assure II) (DAS, 2010b; DuPont, 2010). 

Although quizalofop-P-ethyl is registered for use on soybean, it is not among the 10 most 

frequently used herbicides on this crop. It is sometimes used to eliminate volunteer corn from 

1 Reference to the DuPont AssureTM II label is for illustration only, and is not intended to infer 

any recommendation for the use of this product by APHIS or the USDA.

Page 4-23

 
soybean fields. The most frequently used ACCase inhibitor on soybean is clethodim, an 

herbicide in the “dim” family and the fifth most widely used herbicide in the Heartland, the 

Northern Crescent, and the Northern Great Plains. The “fop” herbicides traditionally have not 

been used to control weed species in cornfields because, like other grasses, corn is sensitive to 

ACCase inhibitors. DAS-40278-9 corn, however is resistant to quizalofop. 

Current Glufosinate Use

Glufosinate is a nonselective herbicide that is used to control grasses, sedges and broadleaf

weeds. Since it is a nonselective herbicide it injures or kills crop plants that it contacts. Several 

crop plants have been modified by inserting a gene that produces an enzyme which detoxifies 

glufosinate by converting the herbicide into a non-active form. Bayer Crop Science has 

registered glufosinate for use on glufosinate-resistant crops including corn and soybean. Ignite

280 SL Herbicide (EPA Reg. No. 264-829) is a commercially available glufosinate containing

herbicide with directions for use on glufosinate-resistant crops (DAS, 2012a).

Glufosinate herbicides contain the active ingredient phosphinothricin and are in the phosphinic 

acid family of herbicides. The herbicide acts by blocking the plant enzyme glutamine 

synthetase, which is responsible for nitrogen metabolism and for detoxifying ammonia, a byproduct of plant metabolism. The exposed plant dies by the over-accumulation of ammonia 

(US-EPA, 2008). First registered with EPA in 1993, initial glufosinate end-use products were 

designed for home owners; light industrial, non-food users; and farmstead, weed-control users 

(OSTP, 2001). Glufosinate, a water soluble herbicide, is approved for use on apples, berries, 

canola, corn, cotton, currants, grapes, grass grown for seed, potatoes, rice, soybeans, sugar 

beets, and tree nuts. Non-crop areas where glufosinate is registered for use on include 

residential lawns and industrial and public areas. Products include RelyTM, RemoveTM, AEHTM, 

DerringerTM, and FinaleTM (US-EPA, 2008). IgniteTM/LibertyTM glufosinate products are 

registered exclusively for selective over-the-top use on GE LibertyLinkTM corn, cotton, canola, 

rice, and soybean. 

In 2002, it was estimated that glufosinate use in the U.S. for all purposes was 982,324 lb a.i.

(Gianessi and Reigner, 2006). Estimates of annual applications of glufosinate in the U.S. 

indicate that approximately 1,000,000 lb a.i. were applied to agricultural land with the highest 

percentage (90 percent) used on corn (United States Geological Survey, No Date). Based on its 

proprietary data for the period from 2007–2011, EPA estimated that the highest annual 

agricultural uses of glufosinate are in corn (1.3 million lbs), almonds (200,000 lbs), cotton 

(200,000 lbs), grapes (200,000 lbs), canola (100,000 lbs) and soybeans (100,000 lbs)(US-EPA, 

2012d). With the commercial availability of glufosinate-resistant LibertyLinkTM soybean 

beginning in 2009, glufosinate use on soybeans has increased. Glufosinate-resistant soybean 

accounted for less than 1 percent of soybean acreage planted in the U.S. in 2009 with 

approximately 72,000 lb ai glufosinate applied. In 2012, the planted acreage of glufosinateresistant soybeans increased to 3.9 percent, and glufosinate use rose to approximately 

1,536,000 lb (DAS, 2012a) Table 4-3. The map in Figure 4-9 shows the use of glufosinate 

from 2009 prior to the use on soybean. (A more recent version is/is not available). At that time, 

most use of glufosinate was concentrated in the Midwest. 

Page 4-24
Figure 4-9. Estimated Annual Agricultural Use of Glufosinate in the U.S.

Source: (USGS, 2009)

Due to its nonselective activity, glufosinate has a weed management spectrum similar to 

glyphosate and its use has grown, particularly in areas with glyphosate-resistant weeds 

(Southeast Farm Press, 2012). In the southeast in 2011, glufosinate was the ninth most 

frequently used herbicide on soybean. Glufosinate resistance in EnlistTM soybean enables use of

glufosinate as an herbicide on commercially grown soybeans but also provides use as a

selection agent in breeding programs and seed amplification (DAS, 2010b).

Glufosinate-resistant soybeans are a more recent introduction than glyphosate-resistant 

soybeans. The number of acres planted to glufosinate-resistant soybeans has grown steadily but 

is still a very small fraction of total soybean acres. Average seasonal use rate is about a half

pound per acre with just over 1 application per acre made. Glufosinate can also be used as a

pre-plant (burn down) treatment on conventional and glufosinate-resistant soybean, however

volume estimates for this use have a high degree of uncertainty (DAS, 2012a). For the years 

2009-2011only a total of 46,000 lbs were used in a pre-plant treatment and 75% of those

pounds were used in 2011.

Although glufosinate provides an additional means of weed control, it is not as versatile as 

glyphosate. For example, glufosinate needs to be applied to smaller weeds with finer droplet 

sizes and larger carrier volumes to achieve adequate control. This is in part because, unlike 

glyphosate which translocates readily throughout the plant, glufosinate has limited mobility and 

thus requires better coverage for control (hence the larger carrier volumes and smaller droplet 

sizes).

Page 4-25
Application rates of glufosinate range significantly by use pattern, with the highest rate allowed 

for broadcast (ground) spray applications, at 1.5 lbs a.i./A, on orchard nuts and fruits, grapes, 

grasses grown for seed, and golf course turf. On the low end of application rates, labeled uses of 

glufosinate on turf and patio are at 0.03 lbs a.i./A. Multiple applications are allowed by most 

labels, although the interval is not generally specified (US-EPA, 2008). The EPA-registered use 

of glufosinate on LibertyLinkTM (i.e., glufosinate-resistant) soybean includes an initial application 

of glufosinate no higher than 0.66 lb a.i./A (36 fl oz/A) with a minimum of 0.40 lb a.i./A (22 fl 

oz/A). A single second application of glufosinate up to 0.53 lb a.i./A (29 fl oz/A) is approved on 

LibertyLinkTM soybeans, with a seasonal maximum rate of 1.2 lb a.i./A (65 fl oz/A) permitted. 

Glufosinate applications on LibertyLinkTM soybean should be made from emergence up to but not 

including the bloom growth stage and within 70 days of harvesting soybean (Bayer CropScience, 

2011).

Current Glyphosate Use

Current glyphosate use directions approved by EPA for use on glyphosate-resistant corn allow a

maximum pre-emergence application amount of 3.7 lbs glyphosate ae/ac, and two post-emergent 

applications each at 1.125 lbs glyphosate ae/ac (total 2.25 lbs ae/ac). An additional pre-harvest 

application of 0.77 lbs ae/ac can be made. Total seasonal use rate is 6 lbs glyphosate ae/ac . 

Application of glyphosate to soybean is similar with the exception that post-emergent 

applications from 0.75 to 1.5 lbs glyphosate ae/ac (total 2.25 lbs ae/ac/season) can be made.

Third party proprietary market research data indicate that the percentage of glyphosate-resistant

corn acres has grown over the last four years (Table 4-10). Total pounds of glyphosate applied to 

corn have also increased during this time where the percentage of the crop has increased from 

77% treated in 2008 to 90% treated in 2011. In contrast, acres of soybean treated have remained 

fairly constant at 94-96% of the crop (Table 4-11). The application rate and the total 

applications/acre have remained fairly uniform for both crops despite the increase in glyphosate 

resistant weeds. 

Table 4-10. Glyphosate Use on Glyphosate-Resistant Corn

Year Total 

Acres

Gly-Tol 

Acres

Gly-Tol as

% of Total 

Acres

Total Pounds 

Gly

Lbs 

Gly/Acre

Total 

Applications/ 

Acre

2008 86,705,017 66,854,236 77 67,760,400 1.06 1.29

2009 86,409,977 71,071,345 82 68,621,113 1.05 1.28

2010 87,230,005 75,958,684 87 75,582,434 1.11 1.31

2011 91,620,001 82,163,813 90 85,671,957 1.17 1.33

Source:(DAS, 2012d)

Page 4-26
Table 4-11. Glyphosate Use on Glyphosate-Resistant Soybean

Year Total

Acres

Gly-Tol

Acres

Gly-Tol as

% of Total 

Acres

Total Pounds

Gly

Lbs

Gly/Acre

Total

Applications/ 

Acre

2008 74,404,953 71,592,624 96 95,398,687 1.32 1.58

2009 77,584,979 73,219,835 94 96,415,627 1.30 1.55

2010 78,725,007 74,059,182 94 102,162,527 1.38 1.58

2011 74,835,007 71,734,538 96 100,121,452 1.40 1.54

Source: (DAS, 2012c)

Glyphosate use is concentrated heavily in the Midwest, along the Mississippi River, the 

Southeast seaboard, and the Central Valley of California as depicted in Figure 4-10. 

Figure 4-10. Estimated Annual Agricultural Use of Glyphosate in the U.S.

Notes: Map represents average annual pesticide use intensity expressed as average weight (in 

pounds) of a pesticide applied to each square mile of agricultural land and typical use patterns 

over the 5-year period of 1999 through 2004. 

Source: (USGS, 2009; United States Geological Survey, No Date)

Changes in 2,4-D and Glyphosate Use for Enlist DuoTM Herbicide

Proposed new use rates of 2,4-D and glyphosate, the active ingredients in the new DAS Enlist 

DuoTM herbicide formulation, on EnlistTM corn and soybeans are detailed in Appendix 8. 

Page 4-27
Projected 2,4-D Use in Corn and Soybean under the No Action and Action Alternatives

No Action Alternative

In the past 3 years, there has been a 38% increase in the amount of 2,4-D applied to corn (Table 

4-8) and an 80% increase in the amount applied to soybean over the past 5 years (Table 4-9)

(DAS, 2012d; DAS, 2012c). These increases are due to the increased fraction of the crops treated 

and the increase in acreage of both crops. Although the acreage of corn and soybean is not 

expected to increase substantially beyond current levels, the percentage of the crop treated is 

expected to continue to increase as glyphosate resistant weeds become more widespread. Thus,

under the No Action Alternative, an increase in baseline use of 2,4-D on corn and soybean is 

expected. Historically, the highest recorded use of 2,4-D is its application to 14% of the U.S.

corn acres in 1994 (USDA-NASS, 2011) which would result in a further 4% increase in 2,4-D

use in corn. However, APHIS sees no reason that this share is an upper limit and 2,4-D use in 

either crop as a pre-plant burndown could reasonably be expected to follow the distribution of 

glyphosate-resistant weeds in the corn and soybean crop. 

Third-party proprietary market research demonstrates that approximately 98% of glyphosateresistant soybean acres receive at least one glyphosate application (burn down and/or post 

emergent). A small population of farmers (~4%) that purchase glyphosate-resistant soybeans 

elect not to make a post-emergent glyphosate application. The market research also indicates 

that 22% of planted soybean acres currently receive a burn-down (pre-plant or pre- emergence) 

herbicide application. For corn, ~10% of farmers that purchase glyphosate-resistant corn elect

not to make a post-emergent glyphosate application. The market research also indicates that 22%

of planted corn acres currently receive a burn-down (pre-plant or pre-emergence) herbicide

application.

Using third party market data, DAS has estimated that 5% of U.S. corn or soybean acreage had

glyphosate-resistant weeds in 2010, and that the percentage would grow to 10% of soybean/corn 

acreage by 2015 and to 30% by 2020 (Figure 4-13). This is consistent with but less aggressive

than predictions made by other others, (Foresman, 2009; Farm Industry News, 2013).

Assuming that by 2020, 30% of corn and soybean fields will be infested with glyphosate 

resistant weeds, it is reasonable to assume that up to 30% of corn and soy growers will use 2,4-D 

on their crops for burndown applications. Currently 12% of the soy crop is treated with 2,4-D 

(Table 4-9). If that percentage increases to 30%, 2,4-D use on soy would be expected to increase 

from 5.4 to 13.5 million pounds ( a factor of 30/12=2.5). Likewise, 10% of the corn crop is 

treated with 2,4-D (Table 4-8). If 30% were treated, the amount of 2,4-D applied would increase 

from 5.4 million pounds to 16.2 million pounds. Assuming 2,4-D use does not increase in other 

crop or non-crop applications, the total applied to crops is predicted to increase from 25.6 million 

pounds to 44.5 million pounds resulting in a 74% increase in crop use of 2,4-D and a 29% 

increase in total 2,4-D use (Table 4-14) under the No Action Alternative.

Page 4-28
Source: (DAS, 2011a).

Figure 4-11. Projected corn and soybean acres infested with glyphosate resistant weeds. 

Action Alternatives

There is considerable uncertainty regarding the projected use of 2,4-D on DAS-40278-9 corn,

DAS-68416-4 soybean, and DAS 44406-6 soybean should all be granted non-regulated status. 

The adoption rate would depend on the availability of the traits in high performing varieties, the 

extent to which weeds are difficult to control with existing herbicides, cost of the new product 

relative to existing varieties, to name a few. 

EPA has approved 2,4-D for use on other major agricultural crops at rates greater than those 

proposed for DAS-68416-4 soybean, DAS 44406-6 soybean or DAS-40278-9 corn. The 

proposed maximum 2,4-D application rate for soybean is the same as that currently approved for 

use on field corn and popcorn (US-EPA, 2005), which are typically grown in the same areas as 

soybeans and often in the same fields in rotation with soybean. Utilizing the historically

consistent data from the current and broad use of glyphosate on DAS-40278-9 corn (Table 4-10), 

DAS has estimated that farmers who grow EnlistTM corn will use an average of 0.875 lbs 2,4-D

ae/ac/application with an average of 1.33 applications per season. Similarly, utilizing the

historically consistent data from the current and broad use of glyphosate on soybean (Table 4-11)

plus field trial data on weed control with various herbicide application rates, DAS has estimated 

that farmers who grow EnlistTM soybean will use an average of 0.875 lbs 2,4-D ae/ac/application 

with an average of 1.54 applications per season (includes burn down and post emergent 

applications). The application rate of 0.875 lbs 2,4-D ae/ac is the midpoint between the medium 

Page 4-29
and high rates allowed on the Enlist DuoTM label and is consistent with the glyphosate rate needed

for weed control. As Enlist DuoTM contains an ~1:1 ratio of 2,4-D and glyphosate, nearly identical 

rates of 2,4-D and glyphosate will be applied.

DAS provided to APHIS three projections of 2,4-D use in corn and soybean:

Scenario 1 assumes growers will only apply Enlist DuoTM to DAS-40278-9 corn, DAS-68416-4 

soybean, or DAS 44406-6 soybean where growers are facing or actively trying to prevent the 

establishment of glyphosate-resistant weeds. Additionally this scenario also assumes that all

farmers with corn or soybean acres that have glyphosate resistant weeds will plant DAS-40278-9

corn or DAS-68416-4/ DAS 44406-6 soybeans and will use Enlist DuoTM herbicide. This is an 

overestimate of the use of 2,4-D given the fact that other weed control options are available. 

Assuming that minimal additional acreage would be treated to prevent glyphosate resistant weeds 

from becoming established, and using the assumptions set forth above regarding total corn or 

soybean acres, application rates and applications per season, the following formula was used to 

calculate total lbs of 2,4-D ae that might be used on DAS 40278-9 corn, DAS-68416-4 soybean, 

or DAS 44406-6 soybean:

Corn

92MM acres x 30% resistant weeds (in 2020) x .875 lbs ae/ac/application x 1.33 

applications/season = 32MM lbs 2,4-D ae per year (Table 4-14). This represents an

approximate six-fold increase in 2,4-D use on corn in 2020 compared to the volume of 2,4-D 

currently used on corn in 2011 and a 100 % increase compared to the volume predicted to be 

used under the No Action Alternative for 2020.

Soybean

76MM acres x 30% resistant weeds (in 2020) x .875 lbs ae/ac/application x 1.54 

applications/season = 31MM lbs 2,4-D ae per year (Table 4-14). This represents an 

approximate six- fold increase in 2,4-D use in 2020 compared to the volume of 2,4-D

currently used on soybean in 2011 and a 130 % increase compared to the volume predicted 

under the No Action Alternative for 2020.

Scenario Two. The second scenario assumes that all acres of DAS 40278-9 corn, DAS-68416-4

soybean, or DAS 44406-6 soybean would receive applications of Enlist DuoTM, regardless of

weed control need, and thus relies on estimates of what the projected market share of these two 

crops will be:

DAS sells corn and soybean seed through its subsidiary seed companies, i.e., Mycogen Seeds, 

Renze Seeds, Dairyland Seed, Pfister Seeds, Brodbeck Seeds, Triumph Seed, Prairie Brand Seed

and Hyland Seeds. Through these subsidiaries, DAS currently has <5% of the market share for 

field corn and silage corn and <3% of the market share for soybean. At this time, DAS is not

planning to breed DAS-40278-9 corn into all of its corn hybrids, so DAS-40278-9 corn would 

occupy considerably less than DAS’s current < 5% of the market. Similarly, DAS is not 

planning to breed DAS-68416-4 soybean into all of its soybean varieties, so EnlistTM soybean 

would occupy less than DAS’s current < 3% of the market. However, for purposes of this 

Page 4-30
estimate, 5% and 3% will be used as a minimum potential for DAS-40278-9 corn and EnlistTM

soybean acreage, respectively.

DAS is interested in and is pursuing licensing agreements with additional corn and soybean seed 

companies to breed DAS-40278-9 corn and DAS-68416-4 or DAS-44406-6 soybean into a

licensee’s corn and soybean germplasm, respectively. To date, two licensing agreement have

been made representing ~35% of the soybean market but no agreements have been made for 

corn. Through natural growth and these licensing arrangements it is reasonably possible that, at 

maturity, approximately 45% of the corn and soybean germplasm could have the EnlistTM trait and 

these corn and soybean varieties could be planted on up to 45% of the total corn and soybean

acreage. Due to the technical aspects of corn and soybean seed breeding, rapid improvement of 

germplasm and stacking with other traits, this level of adoption of DAS-40278-9 corn, DAS68416-4 soybean, or DAS-44406-6 soybean is estimated to take 5-10 years to reach maturity

(maturity in 2018-2023). 

Corn:

Assuming application rates of 2,4-D are as described above: an average of 0.875 lbs 

ae/ac/application with 1.33 applications per year and 90% of acres estimated (based on current 

glyphosate application information from proprietary third party data that only 90% of glyphosate 

resistant corn is sprayed with glyphosate) :

At present market share of 5%, 2,4-D use on corn is expected to double compared to 2011:

92MM acres x 5% market share x 90% DAS-40278-9 corn acres treated x 0.875 lbs

ae/ac/application x 1.33 applications per DAS-40278-9 corn acre = 4,709,250 additional lbs 2,4-

D ae per year compared to 5.4 million pounds in 2011. 

At a market share of 45%, 2,4-D use on corn might increase 8 fold compared to 2011 levels.

92MM acres x 45% market share x 90% DAS-40278-9 corn acres treated x 0.875 lbs

ae/ac/application x 1.33 estimated applications per DAS-4078-9 corn acre = 43,361,325 lbs 2,4-

D ae per year.

Soybean:

Assuming application rates of 2,4-D are as described above: an average of 0.875 lbs 

ae/ac/application with 1.54 applications per year and 100% of acres are treated:

At a market share of 45%, 2,4-D use on soybean is expected to increase approximately nine-fold 

compared to 2011 levels.

76MM acres x 45% market share x 100% DAS-68416-4 soybean acres treated x 0.875 lbs 

ae/ac/application x 1.54 estimated applications per EnlistTM soybean acre = 46,084,500 lbs 2,4-D

ae per year.

Scenario Three: The third scenario assumes that all current glyphosate-resistant corn and 

soybean acres would be planted to hybrids that also contain the DAS-40278-9 corn, DAS-68416-

Page 4-31
4 soybean, or DAS44406-6 soybean traits. This is an unrealistically high estimation but provides 

an upper confidence level on 2,4-D volume. It is unrealistic to assume that all glyphosate 

resistant corn and soybean will be replaced by the EnlistTM products. First, not all growers will be 

faced with glyphosate resistant weeds and such growers may have little economic incentive to 

adopt EnlistTM corn or soybean. Second, other herbicide resistant soybean varieties are on or 

expected to appear on the market, such as glufosinate, dicamba, isoxaflutole, and mesotrione 

resistant varieties so competition is expected to reduce market share. Third, corn is already 

resistant to 2,4-D and dicamba for at least part of its growth cycle, and thus some growers may 

not value this trait in corn. Even with this extreme assumption, the estimated 2,4-D volume is 

only a 17-fold increase in 2,4-D use on corn and a fourteen fold increase on soybean compared to

the current use of 2,4-D on existing varieties, calculated as follows:

From Table 4-10, 82MM acres of the 92 MM total corn acres are planted to glyphosate-resistnat

corn. Using the same application information and other assumptions used in the previous two

scenarios, the 2,4-D volume can be estimated as follows:

82MM glyphosate-resistant acres x 90% DAS-40278-9 corn acres treated x 0.875 lbs 

ae/ac/application x 1.33 estimated applications per DAS-4078-9 corn acre = 85,884,750 lbs 2,4-

D per year.

For soybean, at least 32% of the market (24MM acres) will not contain the DAS-68416-4 or 

DAS-44406-6 soybean traits, due to one developing technology that will be a direct competitor 

to the EnlistTM Weed Control System. Correcting for this market share, the maximum acreage that 

might be planted to DAS-68416-4 or DAS 44406-6 soybean traits is 52MM acres (76MM24MM). Using the previously applied assumptions for soybean, 2,4-D volume is estimated as 

follows:

52MM glyphosate-resistant acres x 100% DAS-68416-4/DAS 44406-6 soybean acres treated x 

0.875 lbs ae/ac/application x 1.54 estimated applications per DAS-68416-4/DAS-44406-6 

soybean acre = 70,070,000 lbs 2,4-D per year.

Other Estimates of 2,4-D Use on EnlistTM Corn and Soybean.

Benbrook (Benbrook, 2012) projected much higher 2,4-D use rates on DAS-40278-9 corn (30 

fold) than any of the scenarios noted above. One major discrepancy is his assumption that 2,4-D 

use on corn may increase to 55% of planted corn acres by 2019. This is a much larger estimate 

than DAS made (30-45%) based on its potential for licensing of its technology to corn seed 

breeders. He also assumes a much higher use rate. Both Benbrook and DAS estimate a 

comparable application rate of 0.84 and 0.875 lbs/acre, respectively. However Benbrook projects 

that the frequency of applications will increase to 2.3 applications/year, while DAS estimates the 

average number of applications to be 1.33 per year. Historically, corn growers have used 3-4 

different herbicide chemistries even after the introduction of Roundup Ready corn. If growers 

continue to use other modes of action, it is unlikely that 2,4-D applications will rise to 2.3 

applications/year. Therefore, USDA considers the Benbrook projection to be an overestimate. 

Summary of Projected 2,4-D Use

Page 4-32
The information from the calculations described above are summarized in Table 4-14. Under the 

No Action Alternative, 2,4-D use is expected to increase to 82.8 million pounds for all uses of 

2,4-D where 44.5 million pounds are applied to crops. The predicted 2020 crop usage 

constitutes an increase of nearly 75% compared to the volume of 2,4-D used on crops in 2011 

(44.5 million pounds vs25.6 million pounds).

Under the Action Alternatives, three scenarios were considered (I, II, and III). Under Scenario I, 

a six fold increase in 2,4-D use is estimated for both corn and soybean compared to current 

levels. Under Scenario II, an 8 fold increase is estimated for corn and a 9 fold increase is 

estimated for soybean. Under Scenario III, a 17 fold increase is estimated for corn and a 14 fold 

increase is estimated for soybean. These calculations are summarized in Table 4-14. Total crop 

2,4-D use is predicted to range from 98.6 million pounds to 214.5 million pounds, depending on 

the scenario and Alternative. 

Compared to levels of 2,4-D used in 2011, the predicted increase in crop 2,4-D use under the 

Preferred Alternative would be approximately 204% to 588%. However compared to the No 

Action Alternative estimation for 2020, the increase on crop use is estimated to range from 75%-

296%. 

Under Alternative 3 where only corn would be deregulated, the increase of crop 2,4-D use 

predicted under the three scenarios ranges from an increase of 136% 370% compared to the 

current situation. Relative to the No Action Alternative estimation for 2020, the increase ranges 

from 36% to 169%. 

Under Alternative 4, where only soy would be granted non-regulated status, the increase of crop 

2,4-D use predicted under the three scenarios ranges from an increase of 201% 316% compared 

to the current situation. Relative to the No Action Alternative estimation for 2020, the increase 

ranges from 39% to 139%.

Note that even under Scenario I which predicts the smallest fold increase in 2,4-D use, USDA 

considers the estimate to be high because it assumes an unrealistically high market share. Thus 

while 2,4-D use is expected to increase under the Action Alternatives, the difference from the 

predicted No Action is expected to be less than the 75% increase noted in Table 4-14.

Currently, 2,4-D is the third most frequently used herbicide in the U.S (an estimated 64 million 

pounds were used in 2011) after glyphosate (an estimated 225 million pounds were used in 2011) 

and atrazine (an estimated 77 million pounds were used in 2011) (Table 4-15). Levels of atrazine 

use have stayed fairly constant over the past decade but use of glyphosate and 2,4-D have 

continued to increase. Based on the assumptions made, it is estimated that 2,4-D use will surpass 

atrazine use by 2020 under both the No Action and Action Alternatives. 

Page 4-33
Table 4-12. Projected 2,4-D Use Under Four Alternatives. 

Alternative 2 (EnlistTM corn + soybean)

actual 2,4-

D

(millions 

of 

pounds)

projected 2,4-D

use in 2020 

under No Action

(NA)

Alternative

Projected 2,4-D use based on 

DOW estimates for 2,4-D use on 

2,4-D corn and soybean 

(millions of pounds)

2011

increased 

burndown1

Scenario 

I

2

Scenario 

II3

Scenario

III4

crops 25.6 44.5 77.8 104.1 176.2

turf and ornamental 24.3 24.3 24.3 24.3 24.3

range/pasture/industrial 

management 14.0 14.0 14.0 14.0 14.0

corn 5.4 16.2 32.0 43.3 85.9

soybean 5.4 13.5 31.0 46.0 70.1

total 2,4-D 64.0 82.8 116.1 142.4 214.5

% increase in crop 2,4-

D relative to No Action 

2020 75% 134% 296%

% increase in total 2,4-

D relative to No Action

2020 40% 72% 159%

Alternative 3 (EnlistTM corn only)

2011

increased 

burndown1

Scenario 

I

2

Scenario 

II3

Scenario

III4

crops 25.6 44.5 60.3 71.6 119.6

Turf and ornamental 24.3 24.3 24.3 24.3 24.3

range/pasture/industrial 

management 14.0 14.0 14.0 14.0 14.0

corn 5.4 16.2 32.0 43.3 85.9

soybean 5.4 13.5 13.5 13.5 13.5

total 2,4-D 64.0 82.8 98.6 109.9 157.9

% increase in crop 2,4-

D relative to NA 2020 36% 61% 169%

% increase in total 2,4-

D relative to NA 2020. 19% 33% 91%

Page 4-34
Alternative 4 EnlistTM (soybean only)

2011

increased 

burndown1

Scenario 

I

2

Scenario 

II3

Scenario

III4

crops 25.6 44.5 62.0 77.0 106.5

Turf and ornamental 24.3 24.3 24.3 24.3 24.3

range/pasture/industrial 

management 14.0 14.0 14.0 14.0 14.0

corn 5.4 16.2 16.2 16.2 16.2

soybean 5.4 13.5 31.0 46.0 70.1

total 2,4-D 64.0 82.8 100.3 115.3 144.8

% increase in crop 2,4-

D relative to NA 2020 39% 73% 139%

% increase in total 2,4-

D relative to NA 2020. 21% 39% 75%

1

Assumes 2,4-D applied to 30% of corn and soybean crop

as preplant burndown. 2

I estimate (30% glyphosate resistant weeds)= 6X current 

soy and corn use.

3

II estimate (DAS 45% market share corn and soy)= 9x current soy and 8X current 

corn

4

III estimate (all corn and soy less competitor market share)=14X current soy and 

17X current corn

Source: (DAS, 2013d).

Table 4-13. Top Three Herbicides-Total Crop Use in 2002, 2011 and Estimated Use Under

Alternatives (millions of lbs)

2002 2011

2020 

(No Action)

2020 

(Preferred)

2020 

(Alt 3)

2020 

(Alt 4)

glyphosate 102 225 225 225 225 225

atrazine 77 77 77 77 77 77

2,4-D 40 64 83 116-215 99-160 100-145

Source: (DAS, 2013d).

Projected use of Quizalofop on DAS 40278-9 Corn

Changes in Quizalofop Use Directions with EnlistTM Weed Control System

Quizalofop is currently registered for use on soybean and no changes in the use of quizalofop on 

soybean are projected. 

Page 4-35
Quizalofop is not yet registered for use on corn. It’s use as a post-emergent herbicide on corn is a 

proposed new use2 (DAS, 2010b). The petitioner has indicated that “fop” herbicides could be 

used to maintain seed purity in DAS-40278-9 corn breeding nurseries, hybrid production fields, 

and generally for the control of grass weeds in corn. Table 4-16 provides a summary of the 

current labeled uses of quizalofop in comparison with proposed application rates and directions 

for use on DAS-40278-9 corn. 

In current registered uses of quizalofop, the EPA has approved single application rates ranging 

from 0.034 to 0.082 lbs ai/acre (38 g ai/ha to 92 g ai/ha), depending on the weed species, with 

the highest maximum seasonal application rate being 0.206 pounds ai/acre (231 g ai/ha) for weed 

control in mint (DAS, 2011b). Upon EPA approval of the herbicide registration amendment, a

quizalofop herbicide (e.g., Assure II ) would be available for use on DAS-40278-9 corn.

Whether used as a selection agent or as an herbicide, the proposed use directions would

essentially be the same. The proposed directions for use of quizalofop on DAS-40278-9 corn

would allow up to two post emergent applications from the V2 to V6 growth stage (Figure 4-14).

Application rates are 0.034-0.082 lbs ai/ac. The total amount that could be applied in a season is 

0.082 lbs ai/ac (DAS, 2011b). The maximum seasonal rate for quizalofop on DAS-40278-9 corn

would be less than or equal to the maximum seasonal rate on the label for all other crops. DAS40278-9 corn has proven tolerant to quizalofop post-emergent application rates of up to 184 g 

ai/ha (0.164 lbs ai/acre) in field trials (DAS, 2011c). The proposed maximum application rate is 

also the seasonal maximum application rate (DAS, 2011c). This maximum application rate is 

less than that currently approved for use of quizalofop for control of grassy weeds in soybeans 

and cotton, where a seasonal maximum application rate of 139 g ai/ha (0.124 lb ai/acre) is 

approved (DAS, 2011c). 

Table 4-14. Comparison of Current and Proposed Application Rates for Quizalofop

Crop Stage

Current Use Pattern for 

Quizalofop on Soybeans and 

Cotton

Proposed New Use on DAS-40278-9 Corn

Maximum 

Application 

Rate 

(lb/acre)1,2

Directions 

and Timing

Maximum 

Application 

Rate 

(lb/acre)1,2

Directions and Timing

Postemergence

0.082

Apply 0.034 to 

0.082 lb/acre 

per application.

Do not exceed 

a total of 0.124 

lb/acre per 

0.034 to 0.082

Apply 0.034 to 0.082 

lb/acre per application from 

V2 – V6 Growth stages.

Do not make more than 2 

applications.

Do not exceed a total of 

2

As required under FIFRA, metabolism and residue data, along with proposed labeling changes, will be submitted to 

the EPA for the use of “fop”-type herbicides (specifically quizalofop) in DAS-40278-9 Cornfields (page 18 of the 

Petition). Under FIFRA, it is unlawful to use an herbicide “in a manner inconsistent with its labeling” without an 

experimental use permit issued (7 U.S.C. 136j). Quizalofop is currently under registration review

(http://www.epa.gov/oppsrrd1/registration_review/) by the EPA with a Final Decision expected in 2013 (EPA-HQOPP-2007-1089 at http://www.regulations.gov, accessed 3/2011).

Page 4-36

 
Crop Stage

Current Use Pattern for 

Quizalofop on Soybeans and 

Cotton

Proposed New Use on DAS-40278-9 Corn

Maximum 

Application 

Rate 

(lb/acre)1,2

Directions 

and Timing

Maximum 

Application 

Rate 

(lb/acre)1,2

Directions and Timing

season. 0.082 lb/acre per season.

Do not apply later than V6 

growth stage.

Total 

Annual 

Maximum 

Application

0.124 --- 0.082 ---

Source: (DAS, 2010a).

Notes:

1. Active ingredient. 

2. 1 lb/acre is the equivalent of 1,120 g/hectare.

Source: (DAS, 2012b).

Figure 4-12. Proposed Use Pattern of Quizalofop on DAS 40278-9 Corn

Page 4-37
Under the No Action Alternative and Alternative 4, EnlistTM corn would not be deregulated and 

quizalofop could not be used on currently available corn varieties due to its inherent sensitivity. 

No changes are anticipated in the use of quizalofop on soybean. 

Under the Preferred Alternative and Alternative 3, DAS-40278-9 corn would be deregulated. 

Because, unlike all other corn, DAS-40278-9 corn is resistant to quizalofop, new uses for 

quizalofop may arise including the control of glyphosate resistant grasses in corn. A 

determination of nonregulated status of DAS-40278-9 corn, with EPA-approved use of 

quizalofop on corn, has the potential to result in an increase in the annual amount of quizalofop 

use. Although six grass species have developed resistance to glyphosate in the US (Jungle rice,

Goosegrass, Italian Ryegrass, Rigid Ryegrass, Annual Ryegrass and Johnson grass), glyphosate 

remains an effective grass herbicide because the acreage of the affected area is still small. Hence, 

in the near future it is not expected that quizalofop will be used to control grass weeds in corn. 

One of the major uses of quizalofop is to control volunteer corn in soybean. It is expected that 

this use of quizalofop to control volunteer corn will decrease on farms that have adopted DAS40278-9 corn, under the Preferred Alternative and Alternative 3. 

DAS anticipates that the primary use of quizalofop will be to enhance the purity of lines bred 

with the DAS 40278-9 trait. The expected primary use is as a selection agent, to remove (kill) any

corn plants in the seed propagation nursery that do not contain the DAS 40278-9 trait. It could 

find more widespread use to control grassy weeds in corn if other herbicide control options prove 

to be unsatisfactory. E.I. DuPont Company (DuPont) has submitted a label amendment (Assure II,

EPA Reg. No.352-541, active ingredient quizalofop) to provide new directions for quizalofop use

as a selection agent in growing seed corn and as a grass herbicide for use in corn.

There are two applications considered in predicting the use of quizalofop on DAS 40278-9

corn: Use as a selection agent in producing hybrid seed corn, and use as an herbicide to 

control glyphosate-resistant grasses. In the foreseeable future, the latter is not considered 

likely given the effectiveness of glyphosate in controlling grass weeds. Hence projections 

are only considered for the use of quizalofop in seed corn production.

Seed Corn Production: The production of hybrid seed corn requires approximately 1 acre of 

nursery to produce sufficient hybrid seed to plant 125 acres the following season. Two

scenarios are presented to bound the range. The first scenario, the lower bound, uses DAS 

current 5% market share for field and silage corn. The second, upper bound, assumes DAS 

market share will expand to 45%.

Scenario 1: 5% market share for field and silage corn.

92MM acres /125 acres nursery/acre of field corn x 5% market share x 0.082 lbs 

ai/ac/application x 1 application = 3018 lbs quizalofop.

Scenario two: 45% market share for field and silage corn.

92MM acres /125 acres nursery/acre of field corn x 45% market share x 0.082 lbs 

ai/ac/application x 1 application = 27,158 lbs quizalofop.

Page 4-38
Note that if just one percent of the adopters had previously used quizalofop to manage volunteer 

corn in soybean, either increase will be offset by a corresponding decrease in quizalofop that will 

no longer be used to manage corn volunteers. For example if 1% of the soybean growers no 

longer use quizalofop to control volunteer corn and assuming a 5% market share of DAS-40278-9 

corn is grown in rotation with soybean, the decrease in quizalofop is calculated as follows:

76MM acres soybean x 5% market share of DAS-40278-9 corn adopters x 1% no longer using 

quizalofop for volunteer control x 0.082 lbs ai/ac/application x 1 application=3116 pounds.

Thus the small increase in quizalofop use that is expected for corn seed production under the 

Preferred Alternative 2 and 3 is likely to be offset by a corresponding or larger decrease in 

quizalofop use by soybean growers who had previously used quizalofop to manage corn 

volunteers. Accordingly, it is expected that quizalofop use will decrease overall under the 

Preferred Alternative and Alternative 3.

Glufosinate Proposed Use on DAS-68416-4 Soybean

Under the No Action Alternative, glufosinate resistant lines of corn and soybean will still be 

available (Liberty LinkTM). As noted earlier, the planting of glufosinate resistant soybean increased 

three fold between 2011-2012 and further increases can be anticipated under the No Action 

Alternative. The Action Alternatives will not impact the availability of glufosinate resistant corn 

and soybean varieties. In all likelihood, glufosinate and glyphosate resistance traits will be stacked 

with resistance to 2,4-D and growers will have the flexibility to use glufosinate, glyphosate, and 

2,4-D as appropriate. Most likely, the use of glufosinate would not increase under the Action 

Alternatives relative to the No Action Alternative. Possibly, glufosinate use will decrease relative 

to the No Action Alternative if 2,4-D is considered a more favorable option for glyphosate 

resistant weed control compared to glufosinate. 

References

Bayer CropScience. 2011. "Ingite 280 SL Herbicide Label 5a " Bayer CropScience 2011. Web. 

September 28 2011 http://fs1.agrian.com/pdfs/Ignite_280_SL_Herbicide_Label5a.pdf.

Benbrook, Charles M. 2012. "Impacts of genetically engineered crops on pesticide use in the 

U.S. -- the first sixteen years." Environmental Sciences Europe 

24.24. http://www.enveurope.com/content/24/1/24.

Burton, J.D., J.W. Gronwald, D.A. Somers, B.G. Gengenbach, and D.L. Wyse. 1989. "Inhibition 

of corn acetyl-CoA carboxylase by cyclohexanedione and aryloxyphenoxypropionate 

herbicides." Pesticide Biochemistry and Physiology 34: 76-85.

DAS.2012a. "DAS comments to APHIS-2012-0019. Stewardship. Herbicide volume estimate on 

soybean. off target exposure. trait stacking. 2,4-D toxicity evaluation. analysis for the 

presence of dioxins and furans. errata. non ge soybean. regulatory status of herbicides 

that may be used on enlist soybean, 2,4-D choline formulation, lack of toxicological or 

biological synergistic effects between glyphosate and 2,4-D, auxin resistant waterhemp, 

impact of enlist on herbicide use."

DAS.2011a. "Economic and Agronomic Impacts of the Introduction of DAS-40278-9 Corn on 

Glyphosate Resistant Weeds in the U.S. Cropping System." Supplemental Information for 

Page 4-39
Petition for Determination of Nonregulated Status for Herbicide Tolerant DAS-40278-9 

Corn. Ed. Blewett, T. Craig 202.

DAS.2012b. "EnlistTM Weed Control System." PowerPoint Slide Deck presented June 11, 2012 

to APHIS-BRS and Louis Berger Inc. staff,. Ed. Blewett, T.C. 68.

DAS.2013a. "Information Addressing Questions 1, 2 and 3 from Section A. Herbicide Use 

Issues." DAS-68416-4 Soybean and DAS-40278-9 Corn, Dow AgroSciences Petition 

Numbers 09-349-01p and 09-233-01p, Supplemental Documentation in Support of 

Environmental Assessments: .

DAS.2011b. "Petition for Determination of Nonregulated Status for Herbicide Tolerant DAS444Ø6-6 Soybean." Ed. Mark, S. Krieger: Dow AgroSciences. 

228. http://www.aphis.usda.gov/brs/aphisdocs/11_23401p.pdf.

DAS. 2010a. Petition for Determination of Nonregulated Status for Herbicide Tolerant DAS40278-9 Corn. Submitted by L. Tagliani, Regulatory Leader, Regulatory Sciences & 

Government Affairs. Indianapolis, IN: Dow AgroSciences, LLC.

DAS.2010b. "Petition for Determination of Nonregulated Status for Herbicide Tolerant DAS68416-4 Soybean." Ed. Mark, S. Krieger: Dow 

AgroSciences. http://www.aphis.usda.gov/biotechnology/not_reg.html.

DAS.2012c. "PowerPoint Presentation: EnlistTM Weed Control System." T.C. Blewett, Dow 

AgroSciences LLC,. 68.

DAS.2013b. "Supplemental Documentation in Support of Environmental Assessments in 

Response to Questions 1-3 Received December 12, 2012 regarding DAS-40278-9 corn 

and DAS-68416-4 soybean. Herbicide use issues." Ed. Hoffman, Neil.

DAS. 2013c. "Supplemental Documentation in Support of Environmental Assessments regarding 

DAS-40278-9 corn and DAS-68416-4 soybean. 2,4-D weed resistance prevention and 

management, DAS herbicide formulation, geographic areas where other crops are in 

close proximity or will be rotated with corn/sybean

".

DAS. 2012d. Supplemental Information for Petition for Determination of Nonregulated Status 

for Herbicide Tolerant DAS-40278-9 Corn; Estimate of Herbicide Volume and Impact on 

Environmental Load of Herbicides with the Introduction of Enlist corn (DAS-40278-9). 

Indianapolis, IN: Dow AgroSciences, LLC.

DAS. 2011c. Supplemental Information for Petition for Determination of Nonregulated Status 

for Herbicide Tolerant DAS-40278-9 Corn; Regulatory Overview of 2,4-D and 

Quizalofop Use on DAS-40278-9 Corn. Submitted by T.C. Blewett, Regulatory Leader, 

Regulatory Sciences & Government Affairs. Indianapolis, IN: Dow AgroSciences, LLC.

DAS.2013d. "Supplementary Documentation Regarding Herbicide Use and Weed Resistance 

Management in Support of Environmental Assessments/Environmental Impact 

Statement." Response to follow up questions sent between Feb 2 and May 3, 2013 

regarding DAS-40278-9 corn and DAS-68416-4 soybean. treatment acres, flutiacetmethyl, herbicide use plots based on site of action, weed resistance management 

considerations based on site of action and chemistry family, herbicide use when only one 

herbicide is used, current 2,4-D use, grass weeds.

Devine, M.D., and A. Shukla. 2000. "Altered target sites as a mechanism of herbicide 

resistance." Crop Protection 19: 881-89.

DuPont. 2010. "DuPontTM Assure® II Herbicide Label." 2010. Web. March 31 

2011 http://www.cdms.net/LDat/ld742006.pdf.

Page 4-40
Farm Industry News. 2013."Glyphosate-resistant weed problem extends to more species, more 

farms." Farm Industry News. Web. September 27, 2013.

Foresman, C. 2009. "Syngenta Resistance FighterTM Message Board. Figure 2." 2009. Web. 

Accessed January 16, 2011 http://blog.syngenta‐

us.com/blogs/ask_the_expert/archive/2009/04.aspx.

Gianessi, L.P., and N. Reigner. 2006. Pesticide Use in U.S. Crop Production: 2002 - with 

Comparison to 1992 & 1997 - Fungicides & Herbicides. Washington, DC: Crop Life 

Foundation, Crop Protection Research Institute.

Heap, I. 2011. "The International Survey of Herbicide Resistant Weeds." (2011). Web. April 24, 

2011 www.weedscience.com.

Industry Task Force II. 2005. "2,4-D Research Data." 2005. Web. April 4 

2011 http://www.24d.org/background/Backgrounder-What-is-24D-Dec-2005.pdf.

Kelley, K.B., and D.E. Riechers. 2007. "Recent developments in auxin biology and new 

opportunities for auxinic herbicide research." Pesticide Biochemistry and Physiology 

89.1: 1-11.

Monsanto.2012. "Petition of the Determination of Nonregulated Status for Dicamba-Tolerant 

Soybean MON87708." MON 87708-9. Ed. Monsanto. Missouri: Monsanto. 723.

Nice, G., B. Johnson, and T. Bauman. 2013. "A Little Burndown Madness." 2013. Web. August 

5, 2013 http://extension.entm.purdue.edu/pestcrop/2010/issue1/Burndown.pdf.

OSTP. 2001. Case Studies of Environmental Regulation for Biotechnology: Herbicide-Tolerant 

Soybean. Washington, DC: The White House Office of Science and Technology 

Policy. http://www.whitehouse.gov/files/documents/ostp/Issues/ceq_ostp_study4.pdf.

Powles, S.B., and C. Preston. 2009. "Herbicide Cross Resistance and Multiple Resistance in 

Plants." Herbicide Resistance Action Committee 2009. Web. April 19 

2011 http://www.hracglobal.com/Publications/HerbicideCrossResistanceandMultipleResi

stance/tabid/224/Default.aspx.

Rausch, D.2013. "Differences in herbicide use in corn and soybean." Ed. Hoffman, Neil.

Southeast Farm Press. 2012. "Glufosinate herbicide shortage sparks controversy." 2012. 

Web http://southeastfarmpress.com/cotton/glufosinate-herbicide-shortage-sparkscontroversy.

Tu, M., C. Hurd, and JM Randall. 2001Weed Control Methods Handbook: Tools and Techniques 

for Use in Natural Areas. Ed. Conservancy, The Nature: UC Davis, CA.

United States Geological Survey.No Date. "Estimated Annual Agricultural Usage Map for 

Glyphosate." Pesticide Usage Maps. Ed. National Water-Quality Assessment 

Program. http://water.usgs.gov/nawqa/pnsp/usage/maps/show_map.php?year=02&map=

m1099.

US-EPA.2012a. "2,4-D (030001, 030004) - Screening Level Usage Analysis (SLUA)." Ed. 

Office of Chemical Safety and Pollution Prevention. Washington, D.C.: U.S. 

Environmental Protection Agency. Vol. 

2013. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0330-0007.

US-EPA.2012b. "2,4-D. Human Health Assessment Scoping Document in Support of 

Registration Review." Ed. Office of Chemical Safety and Pollution Prevention. 

Washington, D.C.: U.S. Environmental Protection Agency. 36. Vol. 

2013. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0330-0004.

Page 4-41
US-EPA.2012c. "BEAD Chemical Profile for Registration Review: 2,4-D." EPA-HQ-OPP2012-0330-0006. Ed. Prevention, Office of Chemical Safety and Pollution. 

8. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0330-0006.

US-EPA.2012d. "Glufosinate (128850) Screening Level Usage Analysis (SLUA)." Ed. Office of 

Chemical Safety and Pollution Prevention. Washington, D.C.: U.S. Environmental 

Protection Agency. 2 of Docket Number EPA-HQ-OPP-2008-

0190. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2008-0190-0029.

US-EPA.2008. "Quizalofop Final Work Plan - Registration Review of Quizalofop-ethyl 

(128711) and Quizalofop-p-ethyl (128709)." Ed. Office of Prevention, Pesticides, and 

Toxic Substances,. Washington, D.C.: U.S. Environmental Protection Agency. 8 of 

Docket Number EPA-HQ-OPP-2007-

1089. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2007-1089-0026.

US-EPA. 2005. Reregistration Eligibility Decision for 2,4-D. Washington: U.S. Environmental 

Protection Agency. http://www.epa.gov/oppsrrd1/REDs/24d_red.pdf.

USDA-APHIS. 2010. Plant Pest Risk Assessment for DAS-40278-9 Corn. Riverdale, MD: US 

Department of Agriculture, Animal and Plant Health Inspection Service, Biotechnology 

Regulatory Services.

USDA-NASS. 2009."2007 Census of Agriculture, Organic Production Survey (2008)." 

2011.July 12. 

Web. http://www.agcensus.usda.gov/Publications/2007/Online_Highlights/Organics/inde

x.asp.

USDA-NASS. 2002. Acreage. USDA-NASS: USDA-NASS.

USDA-NASS. 2004. Acreage. USDA-NASS: USDA-NASS.

USDA-NASS. 2007. Acreage. USDA-NASS: National Agricultural Statistics Service.

USDA-NASS. 1995. "Agricultural Chemical Usage." Field Crop Summaries. (1995) 74. Web.

USDA-NASS. 2006. Agricultural Chemical Usage 2005 Field Crops Summary: United States 

Department of Agriculture - National Agricultural Statistics 

Service. http://usda.mannlib.cornell.edu/usda/nass/AgriChemUsFC//2000s/2006/AgriChe

mUsFC-05-17-2006.pdf.

USDA-NASS. 2013. "U.S. Corn Acres." 2013. Web. Aug 5, 2013 

2013 http://www.nass.usda.gov/Charts_and_Maps/graphics/cornac.pdf.

USDA-NASS. 2011. "Usage Search: State - All States/Areas; Year: All Years; Crop: All 

Crops; Agricultural Chemical: Quizalofop, ethyl." 2011. Web. April 19 

2011 http://www.pestmanagement.info/nass/.

USGS. 2009. "Estimated Annual Agricultural Use of Glufosinate in 2009." 2009. Web. 

12/6/2013 http://water.usgs.gov/nawqa/pnsp/usage/maps/compound_listing.php.

Wright, T.R., G. Shan, T.A. Walsh, J.M. Lira, C. Cui, P. Song, M. Zhuang, N.L. Arnold, G. Lin, 

K. Yau, S.M. Russel, R.M. Cicchillo, M.A. Peterson, D.M. Simpson, N. Zhou, J. 

Ponsamuel, and Z. Zhang. 2010. "Robust crop resistance to broadleaf and grass 

herbicides provided by aryloxyalkanoate dioxygenase transgenes." Proceedings of the 

National Academy of Sciences of the United States of America 107.4: 20240-

5. www.pnas.org/cgi/doi/10.1073/pnas.1013154107.

WSSA. 2013. "Herbicide-Resistant Weeds by Site of Action." 2013. Web. 12/6/2013.

Page 4-42
Appendix 5. Common Weeds in Corn and Soybean

Page 5-1
Common Weeds in Corn and Soybean

Weeds are simply plants growing in areas where their presence is undesired by humans (Baucom 

and Holt 2009). Plants that colonize frequently disturbed environments have evolved with 

characteristics or mechanisms that allow them to survive conditions in agricultural environments. 

Weedy plants typically exhibit early germination and rapid growth from seedling to sexual 

maturity, have the ability to reproduce sexually and asexually, and therefore are well adapted to 

agricultural fields (Baucom and Holt 2009).

The presence of weeds in corn and soybean fields is a primary detriment to productivity. Weeds 

are the most important pest complex in agriculture, impacting yields by competing with crops for 

light, nutrients, and moisture. In addition to taking valuable resources from crops, weeds can 

introduce weed seed or plant material to a crop, thereby reducing the market grade of the crop. 

Additionally, weeds can harbor insects and diseases; weeds also can interfere with harvest, 

clogging and causing extra wear on harvest equipment (Loux, Stachler et al. 2008). For 

example, some winter annuals have been found to serve as alternative hosts for the soybean cyst 

nematode, a pest that affects soybean yields in the U.S.

Effective weed management involves an understanding of weed biology and of weed 

management strategies. This section provides an overview of weed types, the weed seed bank, 

and the timing and occurrence of weeds. Also described are the types of weeds that occur in 

corn and soybean. Weed management is discussed in Appendix 3.

Weed Classification

Weeds are classified according to their life cycle, as annuals, biennials or perennials. Weeds are 

also classified as broadleaf (dicots) or grass (monocots). Weeds can reproduce by seed, rhizome 

(underground creeping stems), or other underground part (e.g., buds, bulbs). 

An annual is a plant that completes its lifecycle in one year or season and reproduces only by 

seed. Annuals can be further differentiated into summer or winter annuals. Summer annuals 

appear in the spring or early summer and die prior to or by the first frost, producing seeds within 

the same growing season. These weeds grow rapidly, strongly competing with crops for 

resources, and can outgrow and shade slower-growing crops. These weeds tend to be the most 

problematic weeds in corn and soybeans, as they share a similar life cycle. 

Summer annuals can be further categorized into three groups: small-seeded summer annual 

broadleaf weeds, large-seeded summer annual broadleaf weeds, and summer annual grass weeds 

(Schonbeck 2010). Some small-seeded summer annual broadleaf weeds include pigweeds, 

common lambsquarters, common purslane, galinsoga, and smartweeds. Commonly found largeseeded summer annual broadleaf weeds include velvetleaf, common cocklebur, and morning 

glory. Summer annual grass weeds have small to medium sized seeds and include foxtail, 

crabgrass, and goosegrass.

Winter annuals typically emerge in late summer or early fall, but can also germinate as late as 

early spring. Usually these weeds over-winter as small seedlings and set seed in the spring. 

Page 5-2
These weeds have little effect on warm season crops. Common winter annuals include purple 

deadnettle, henbit, field pennycress, shepherd’s-purse, and chickweed (Schonbeck 2010, Mock, 

Creech et al. 2011).

Biennials have a life cycle of two years or seasons. After persisting as low-growing vegetation 

during their first season, biennial weeds overwinter, then flower and produce seeds in their 

second growing season. Examples of biennial weeds are burdock, bull thistle, poison hemlock, 

and wild carrot.

Perennials are plants that live for more than two years and are typically categorized as simple or 

creeping or invasive perennials. These weed species have root systems that store large amounts 

of food reserves, making them difficult to control. Winter perennials are particularly competitive 

and difficult to control because these weeds re-grow every year from rhizomes or root systems 

(DAS 2010). Canada thistle, bermudagrass, common milkweed, common pokeweed, dandelion, 

johnsongrass are examples of perennial weeds (Penn State University 2009, Mock, Creech et al. 

2011).

Generally, annual grass and broadleaf weeds are considered the most common weed problems in 

corn and soybean (Krausz, Young et al. 2001, DAS 2010). 

Weed Seed Bank

An important concept in weed control is the seed bank which is the reservoir of seeds that are on 

the soil surface and scattered at different depths in the soil. The soil weed seedbank determines

the size and species composition of the weed community within a growing season (Norsworthy 

2012). Under favorable conditions, these seeds have the potential to germinate and emerge, 

creating weed pressure (i.e., competition) in crops. The weed seed bank contains recently 

dropped seeds, older seeds mixed into the soil, tubers, bulbs, rhizomes, and other vegetative 

structures. Climate, soil characteristics, shifts in agricultural management practices, such as 

tillage, crop selection, and weed management practices, affect the density and species 

composition of the seed bank within a given field (Davis, Renner et al. 2005, May and Wilson 

2006, Buhler, Hartzler et al. 2008).

The majority of seeds in the weed seed bank come from the weeds that have grown and set seed 

in the field. Wind, water, animals, and birds can carry seeds, adding to the weed seeds already 

present. Also, manure or other material (e.g., mulch, feed, soil) transported by humans or farm 

equipment from other locations can be indirect sources of weed seed (Renner 2000).

Agricultural soils can contain thousands of weed seeds and a dozen or more vegetative weed 

propagules per square foot (Menalled and Schonbeck 2013). Estimates of weed seeds in Corn 

Belt soils range from 56 to 14,864 seeds per square foot (Renner 2000). Annual weeds produce 

large numbers of seeds. For example, a pigweed plant can shed at least 100,000 mature seeds 

and one lambsquarters plant can produce more than 50,000 seeds (Renner 2000). If left 

untended and without crop competition, giant ragweed can produce approximately 10,000 seeds, 

common waterhemp 70,000 seeds, and waterhemp 100,000 seeds, or more, per plant. Largerseeded broadleaf weeds are not as prolific in comparison to small-seeded summer broadleaf 

weeds, but seed production is still high, with a few hundred to a few thousand per plant 

Page 5-3
(Schonbeck 2010). It has been observed that weeds in agricultural fields produce less seeds as a 

result of competition from the crop, damage from herbicides, and other factors, although these 

weed still produce high numbers of seeds that can affect production (Buhler, Hartzler et al. 

1997). 

Although seedbanks are made up of numerous weed species, generally only a few species will 

comprise 70 to 90 percent of the total seed bank (Wilson 1988, Buhler, Hartzler et al. 1997, 

Renner 2000). For example, common lambsquarters (Chenopodium album) is the dominant 

weed seed in many field soils in the north central region of the U.S. (Michigan) (Renner 2000). 

A second smaller group of weed species may represent 10 to 20 percent of the seed bank 

(Buhler, Hartzler et al. 1997). 

Additionally, only a fraction of the seeds in a weed seed bank germinate and grow each year. 

Birds, rodents, insects, and other animals typically will consume available weed seeds found on 

the soil surface. Some seeds may decay or become unviable in the soil; other seeds may 

germinate but will die. Some seeds can remain dormant in the soil for long periods of time. 

When changes in the cropping system change, creating conditions that are suitable for 

germination and development of a particular weed species, that species can respond rapidly, 

becoming non-dormant and establish itself in the cropping system (Renner 2000, Durgan and 

Gunsolus 2003, May and Wilson 2006, Steckel, Sprague et al. 2007). It is estimated that less 

than 10% of the weed seeds in the soil are non-dormant and able to germinate within a season. 

The remaining dormant seeds thereby serve to extend the longevity of the seed bank (Renner 

2000, PhysicalWeeding 2009). For example, summer annuals can remain viable for years, even 

if buried deeper in the soil, while the larger broadleaf seeds can remain viable for decades 

(Schonbeck 2010). 

The majority of weeds grow from seeds in the top two inches of soil with the most significant 

numbers emerging from only the top one inch of soil (PhysicalWeeding 2009). In general, most 

small-seeded weeds (e.g., foxtail, pigweed) germinate and emerge within the upper half inch of 

the soil surface. The large-seeded summer annual broadleaf weeds are usually found in soils 

below the surface layer (about 0.5 to 2 inches below the surface) and can germinate from soil 

depths of 1.5 inches or more. Summer annual grass weeds germinate predominantly from the 

top inch of soil. Generally, tillage brings these seeds to the surface, where they rapidly grow in 

response to light. The effects of different forms of tillage on the prevalence of weed species are 

discussed further, below.

Weed populations change in response to agricultural management decisions. Collectively, 

management decisions will impart selection pressures1 on the present weed community, resulting 

in weed shifts on a local level (i.e., field level). These weed shifts occur regardless of what the 

selection pressure may be and may result in changes in weed density or weed diversity (Reddy 

1 Selection pressure may be defined as any event or activity that reduces the reproductive 

likelihood of an individual in proportion to the rest of the population of that one individual. In 

agriculture, selection pressure may be imparted by any facet of management in the production of 

a crop, including the type of crop cultivated, strategy of pest management, or when and how a 

crop is planted or harvested.

Page 5-4

 
and Norsworthy 2010, Weller, Owen et al. 2010). Weed shifts are generally most dramatic when 

a single or small group of weeds increases in abundance at the expense of other weed 

populations, potentially dictating the primary management efforts of the grower.

The vertical distribution of weed seeds in the soil is primarily influenced by the tillage system 

used.2 These resulting changes in the distribution of the weed seeds in the weed seedbank will 

impact weed emergence and the resulting weed population in farm fields (Renner 2000). As 

shown in Figure 5-1, the practice of no-till results in a majority of the weed seeds remaining at or 

near the soil surface where they have been deposited (Renner 2000, Shrestha, Lanini et al. 2006, 

Menalled and Schonbeck 2013). In no-till fields with more seeds at the surface, a greater 

diversity of annual and perennial weeds species may occur (Baucom and Holt 2009). Winter 

annuals thrive in soil that is undisturbed from late summer or fall through early summer the 

following year which is best provided by no-till systems. Similarly, biennial weeds are prevalent 

in fields that have been no-till for several years, as they need undisturbed soil for two 

consecutive growing seasons.

Under reduced tillage systems (such as chisel plowing), approximately 80 to 90 percent of the 

weed seeds are distributed in the top four inches, with the majority found at depths ranging from 

two to four inches. Summer annual grass weeds germinate predominantly from the top inch of 

soil with prevalence in shallow and reduced tilled fields (Curran, Lingenfelter et al. 2009). With 

recent increased rates of conservation tillage, there has been an observed decrease in largeseeded broadleaf weeds and an increase in perennial, biennial, and shallow-emerging annual 

grasses, small-seeded broadleaves, and winter annual weed species in those fields (Green and 

Martin 1996, Durgan and Gunsolus 2003, Norsworthy 2012). The growth and spread of some 

perennial species that reproduce by spread of underground structures (e.g., rhizomes) may be 

encouraged by no-till or conservation tillage system which allows these structures to remain 

undisturbed (Buhler, Hartzler et al. 2008, Baucom and Holt 2009, Curran, Lingenfelter et al. 

2009).

2

Tillage represents a mechanical means of weed control and is generally characterized by the 

amount of remaining in-field residue and may be classified as conservation (>30 percent), 

reduced (15-30 percent), or intensive (0-15 percent) CTIC (2008). 2008 Amendment to the 

National Crop Residue Management Survey Summary, Conservation Technology Information 

Center.

Page 5-5

 
Figure 5-1. Vertical Distribution of Weed Seeds in the Soil Profile at Depths of 0 to 2 

inches, 2 to 4 inches, and 4 to 6 inches Affected by Different Tillage Regimes

Source: (Shrestha, Lanini et al. 2006)

Weed seeds become buried approximately four to six inches below the surface as a result of 

increasing tillage (Menalled and Schonbeck 2013). As fewer weeds can germinate when buried,

weed diversity tends to decline and annual large-seeded broadleaves are more prominent 

(Norsworthy 2012). 

These shifts in weed species necessitate changes in weed management strategies. Tillage 

practices must be regularly changed, in a manner similar to that of other agricultural production 

practices, to prevent buildup of any particular species or group of weeds in the soil seedbank.

Weed Emergence/Timing

In addition to weed density, the timing of weed emergence affects how they compete with the 

corn or soybean crop and influences the level of crop yield loss. The critical period of weed 

control (CPWC) is the time during which weeds must be controlled to prevent yields losses. The 

key components defining CPWC are 1) knowing when weeds need to be removed and 2) when 

the crop becomes dominant (Boerboom 2000). Weeds emerging before the CPWC may not 

impact crop yields if those weeds are controlled by the start of the CPWC. Weed competition 

occurring after the end of the CPWC will not affect yield (Boerboom 2000, Knezevic 2007). In 

particular, early in the growing season, the critical period of weed competition is most affected

by: 1) how competitive the different weed species are, 2) the density of weeds, and 3) the relative 

time of weed emergence (Boerboom 2000). 

Corn is more vulnerable to early competition by weeds than soybean, especially when weed 

density is high, when corn is under stress from environmental conditions (e.g., drought, extreme 

90%

27%

12%

9%

66%

25%

1% 7%

63%

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

No-till Chisel Plow Moldboard Plow

Percent Seeds (%)

Tillage System

4-6

2-4

0-2

Soil 

Depth 

(in)

Page 5-6
wet conditions, cold soils), or when the crop is slow to establish (Monsanto 2012). Weed control 

is most critical during the first three to five weeks after emergence of corn seedlings (Sikkema 

and Hamill 2005, ANR 2009). Weed costs in corn begin almost as soon as the corn emerges. 

Weeds that are about 3 to 4 inches tall when corn is at the V-3 to V-4 growth stage3 are going to 

present the most competition. If the weeds are taller than corn, they will shade the crop. Control 

should be begin four to five days (one to two leaves) prior to the beginning of the CPWC

(Knezevic 2007). If weeds are controlled early, after several weeks when the corn canopy 

closes, corn can compete with later emerging weeds by shading them out. Narrow row spacing 

and adequate plant populations promote early corn canopy closure (Rosenberg 2013).

Although weeds do not impact corn yield nearly as much later in the corn growing season, those 

weeds can harbor destructive insect pests, such as thrips, which can carry Fusarium ear rot, and 

armyworms, which can defoliate corn. Additionally, weeds in corn can also reduce silage and 

feed quality, slow harvesters by causing wheel slippage or clogging, raise grain moisture content,

and reduce future corn harvests by adding to the seed bank (ANR 2009). 

In soybean, the later that weeds emerge, the less impact they will have on yield, although weeds 

emerging later can have a negative influence on seed quality and harvest efficiency (Prostko 2013). 

Soybean plants withstand early season weed competition longer than corn because the soybean 

canopy closes earlier (Boerboom 2000). The extent of canopy closure restricts the light available 

for weeds and other plants growing below the soybean. In addition, canopy closure occurs more 

quickly when soybean is drilled or planted in narrow rows (Boerboom 2000, Bradley 2006); 

however, in some studies it has also been observed that, depending on factors such as weed 

species, environmental conditions (i.e., rainfall amounts) and soybean cultivar, soybeans are able 

to compete with weeds with no resulting yield reduction (Krausz, Young et al. 2001). Place et 

al. have determined that larger soybean seeds produce a larger canopy more quickly and are, 

therefore, more successful at outcompeting weeds (Place, Reberg-Horton et al. 2011). Fullseason soybean planting is preferable during the drier late spring conditions; however, summer 

annual weed emergence often occurs at this same time, resulting in a high level of weed 

interference with soybean emergence and establishment (DeVore, Norsworthy et al. 2013).

Common Weeds in Corn and Soybean

To assist growers in managing weeds, individual states, typically through their state agricultural 

extension service, list the prevalent weeds in crops in their area and the most effective means for 

their control (see, e.g., IPM 2004, IPM 2007, University of California 2009). Some of the key 

weed species found in corn and soybean fields are described in the following sections.

Weed species emerge in a particular order throughout the year with each species having one or 

more periods of high emergence. The initial emergence date can vary from year to year, but the 

order stays relatively constant. Figure 5-2 shows the relative emergence of common weed 

species found in summer annual crops such as corn and soybean. Weed emergence timing can 

dictate which weeds will be the most problematic for or be more easily controlled by a specific 

3 Corn at the V3 is approximately 2 weeks after emergence and is ~8 inches tall and at the V4 

growth stage is near or at 12 inches tall.

Page 5-7

 
crop production or weed management practice (Buhler, Hartzler et al. 2008). Weed management 

is discussed in Appendix 3.

Figure 5-2. Relative Emergence of Common Weeds of Summer Annual Crops. 

Source: (Buhler, Hartzler et al. 2008).

Problem Weeds in Corn and Soybean

Based on a survey of growers in 2011, Table 5-1 lists the 10 broadleaf or grass weeds found in 

corn and soybean that growers indicated they most often had to manage in their fields (DAS 

2013). The first column lists those weeds on a national basis and the remaining columns list the 

weeds that are most problematic in each region. Regions that produce very little corn or soybean 

were not included. The Southeast region produces very little corn, but significant amounts of 

soybean; so information for the region was included for soybean but not for corn. Likewise the 

Prairie Gateway produces considerable corn but little soybean and was included in the section for 

corn but not soybean. Many of the problem weeds are present in multiple regions. 

Page 5-8
Table 5-1. National and Regional List of Top Ten Troublesome Broadleaf and Grass 

Weeds in Corn and Soybean in 2011.

Source: (DAS 2013)

Based on the information in Table 5-1, a list of the unique problem weeds in corn and soybean 

are presented in Table 5-2. In some cases the same weed species are listed under two different 

common names in Table 5-1. In Table 5-2, common waterhemp and tall waterhemp are listed as 

waterhemp. Marestail and horseweed are listed as horseweed. Moringglory and field bindweed 

are listed as field bindweed. Thistle is listed as Canada, Russian, or Musk thistle. Foxtail is listed 

as giant, yellow, or green foxtail. 

US Corn Heartland Northern Crescent Northern Great Plains Prairie Gateway

Broadleaf Weeds most treated for

VELVETLEAF VELVETLEAF LAMBSQUARTERS VELVETLEAF PIGWEED, REDROOT

PIGWEED, REDROOT WATERHEMP, COMMON PIGWEED, REDROOT PIGWEED, REDROOT KOCHIA

LAMBSQUARTERS LAMBSQUARTERS VELVETLEAF WATERHEMP, COMMON THISTLE

WATERHEMP, COMMON RAGWEED, GIANT RAGWEED SUNFLOWER VELVETLEAF

COCKLEBUR COCKLEBUR RAGWEED, GIANT COCKLEBUR MORNINGGLORY

RAGWEED, GIANT PIGWEED, REDROOT DANDELION KOCHIA THISTLE, RUSSIAN

KOCHIA RAGWEED THISTLE, CANADA LAMBSQUARTERS BINDWEED, FIELD

MARESTAIL MARESTAIL MORNINGGLORY MARESTAIL COCKLEBUR

RAGWEED MORNINGGLORY COCKLEBUR THISTLE, CANADA THISTLE, MUSK

MORNINGGLORY HORSEWEED THISTLE SUNFLOWER SUNFLOWER

Grass weeds most treated for

FOXTAIL FOXTAIL FOXTAIL FOXTAIL, YELLOW JOHNSONGRASS

FOXTAIL, GIANT FOXTAIL, GIANT QUACKGRASS FOXTAIL SANDBUR

FOXTAIL, YELLOW FOXTAIL, YELLOW FOXTAIL, GIANT FOXTAIL, GREEN WHEAT, VOLUNTEER

FOXTAIL, GREEN FOXTAIL, GREEN FOXTAIL, YELLOW FOXTAIL, GIANT PANICUM, TEXAS

JOHNSONGRASS JOHNSONGRASS CRABGRASS SANDBUR BARNYARDGRASS

CRABGRASS PANICUM, FALL FOXTAIL, GREEN WHEAT, VOLUNTEER SICKLEGRASS

WHEAT, VOLUNTEER CUPGRASS, WOOLLY PANICUM, FALL OAT, WILD

QUACKGRASS BARNYARDGRASS GRASSES, ALL BARNYARDGRASS

PANICUM, FALL QUACKGRASS MILLET, WILD-PROSO CHEAT

BARNYARDGRASS CRABGRASS CUPGRASS, WOOLLY CRABGRASS

US Soybeans Heartland Northern Crescent Northern Great Plains SouthEast

Broadleaf Weeds most treated for

 REDROOT PIGWEED WATERHEMP, COMMON LAMBSQUARTERS VELVETLEAF PIGWEED, REDROOT

COMMON WATERHEMP VELVETLEAF VELVETLEAF WATERHEMP, COMMON MORNINGGLORY

VELVETLEAF RAGWEED, GIANT PIGWEED, REDROOT COCKLEBUR MARESTAIL

COCKLEBUR LAMBSQUARTERS RAGWEED MARESTAIL COCKLEBUR

MARESTAIL COCKLEBUR RAGWEED, GIANT PIGWEED, REDROOT AMARANTH, PALMER'S

LAMBSQUARTERS PIGWEED, REDROOT DANDELION MUSTARD, WILD SICKLEPOD

 GIANT RAGWEED MARESTAIL NIGHTSHADE, BLACK BUCKWHEAT, WILD SIDA, PRICKLY

MORNINGGLORY RAGWEED CHICKWEED, MOUSEEAR LAMBSQUARTERS LAMBSQUARTERS

RAGWEED MORNINGGLORY MORNINGGLORY SUNFLOWER SESBANIA, HEMP

SUNFLOWER WATERHEMP, TALL WATERHEMP, COMMON KOCHIA HENBIT

Grass weeds most treated for

FOXTAIL FOXTAIL FOXTAIL FOXTAIL JOHNSONGRASS

FOXTAIL, GIANT FOXTAIL, GIANT QUACKGRASS FOXTAIL, YELLOW BARNYARDGRASS

JOHNSONGRASS FOXTAIL, YELLOW FOXTAIL, GIANT OAT, WILD CRABGRASS

FOXTAIL, YELLOW JOHNSONGRASS FOXTAIL, YELLOW FOXTAIL, GIANT SIGNALGRASS, BROADLEAF

BARNYARDGRASS CORN, VOLUNTEER CORN, VOLUNTEER FOXTAIL, GREEN RYEGRASS

FOXTAIL, GREEN FOXTAIL, GREEN CRABGRASS BROME, DOWNY WATERGRASS

CRABGRASS QUACKGRASS FOXTAIL, GREEN BROME, JAPANESE BLUEGRASS, ANNUAL

Page 5-9
In summary, there are 25 broadleaf and 22 grass weed species noted from the top ten lists, 

respectively, that required control measures in the major growing regions of soybean and corn. 

Some species such as redroot pigweed were problematic in all regions in both corn and soybean 

fields (marked in green in Table 5-2). Other species such as sicklepod, prickly sida, and wild 

buckwheat were more regional problems. Combining the lists of corn and soybean, there are a 

total of thirteen broadleaf and nine grass weeds, respectively, that are a problem in both corn and 

soybean, four broadleaf and seven grass weeds that are mostly problematic in corn (marked in 

yellow in Table 5-2), and eight broadleaf and six grass weeds that are mostly problematic in 

soybean (marked in blue in Table 5-2). 

Table 5-2. Summary of Problem Weeds Affecting Corn and Soybean.

Broadleaf Weeds Grass Weeds

Corn + 

Soybean Corn Soybean

Corn + 

Soybean Corn Soybean

redroot pigweed henbit wild mustard giant foxtail woolly cupgrass downy brome

lambsquarters Pennsylvania 

smartweed black nightshade yellow foxtail wild-proso millet Japanese brome

waterhemp Russian thistle mousear chickweed green foxtail sandbur broadleaf signalgrass

cocklebur musk thistle hemp sesbania johnsongrass fall panicum ryegrass

giant ragweed palmer's amaranth crabgrass cheat watergrass

kochia sicklepod wheat, volunteer Texas panicum annual bluegrass

horseweed prickly sida quackgrass sicklegrass

common ragweed wild buckwheat barnyardgrass

field bindweed wild oat

sunflower

Canada thistle

velvetleaf

dandelion

Based on the data in Table 3-1 (DAS 2013) .

Notes:

Green: Weeds managed in both corn and soybean 

Yellow: Weeds primarily managed in corn 

Blue: Weeds primarily managed in soybean

References:

ANR, U. (2009) Integrated Weed Management. UC IPM Pest Management Guidelines: Corn 

Baucom, R. and J. Holt (2009). "Weeds of agricultural importance: Bridging the gap between 

evolutionary ecology and crop and weed science." New Phytologist(184): 741-743.

Boerboom, C. (2000) Timing Postemergence Herbicides in Corn and Soybeans. 2011, 

Page 5-10
Boerboom, C. (2000). "Timing Postemergence Herbicides in Corn and Soybeans." Wisconsin 

Crop Management Conference 2000 Proceedings Papers.

Bradley, K. W. (2006). "A Review of the Effects of Row Spacing on Weed Management in Corn 

and Soybean."

Buhler, D. D., R. G. Hartzler, et al. (1997). "Implications of Weed Seedbank Dynamics to Weed 

Management." Weed Science 45(3): 329-336.

The species composition and density of weed seed in the soil vary greatly and are closely 

linked to the cropping history of the land. Altering tillage practices changes weed seed 

depth in the soil, which plays a role in weed species shifts and affects efficacy of control 

practices. Crop rotation and weed control practices also affect the weed seedbank. 

Information on the influence of cropping practices on the weed seedbank should be a 

useful tool for integrated weed management. Decision aid models use information on the 

weed seedbank to estimate weed populations, crop yield loss, and recommend weed 

control tactics. Understanding the light requirements of weed seed may provide new 

approaches to weed management. Improving and applying our understanding of weed 

seedbank dynamics is essential to developing improved weed management systems. The 

principles of plant ecology must be integrated with the science of weed management to 

develop strategies that take advantage of basic plant responses in weed management 

systems for agronomic crops.

Buhler, D. D., R. G. Hartzler, et al. (2008) Relative emergence sequence for weeds of corn and 

soybeans. Sustainable Agriculture 4 

CTIC (2008). 2008 Amendment to the National Crop Residue Management Survey Summary, 

Conservation Technology Information Center.

Curran, W. S., D. D. Lingenfelter, et al. (2009) An Introduction to Weed Management for 

Conservation Tillage Systems - Conservation Tillage Series Number Two. 

DAS (2010). Petition for Determination of Nonregulated Status for Herbicide Tolerant DAS68416-4 Soybean. S. K. Mark, Dow AgroSciences.

Page 5-11
DAS (2013). Supplementary Documentation in Support of Draft Environmental Assessment -

Responses to Questions 4, 6 and 7 from Section B. 2,4-D Use. DAS-686-416-4 Soybean and 

DAS-40278-9, Corn Dow AgroSciences Petition Numbers 09-349-01p and 09-233-01p,, Dow 

AgroSciences LLC: 33.

Davis, A. S., K. A. Renner, et al. (2005). "Weed seedbank and community shifts in a long-term 

cropping systems experiment." Weed Science 53(3): 296-306.

DeVore, J. D., J. K. Norsworthy, et al. (2013). "Influence of Deep Tillage, a Rye Cover Crop, 

and Various Soybean Production Systems on Palmer Amaranth Emergence in Soybean." Weed 

Technology 27(2): 263-270.

Durgan, B. R. and J. L. Gunsolus (2003) Developing Weed Management Strategies that Address 

Weed Species Shifts and Herbicide Resistant Weeds. 2011, 

Green, J. D. and J. R. Martin (1996) Dealing with Perennial Broadleaf Weeds in Conservation 

Tillage Systems. 2011, 

IPM (2004). Crop Profile for Field Corn in Pennsylvania. University Park, PA, Department of 

Agronomy, Penn State University: 21.

IPM (2007). Crop Profile for Corn in the Northern and Central Plains (KS, NE, ND, and SD),: 

26.

Knezevic, S. (2007) Timing Weed Control in Corn to Get the Most Effect. CropWatch 

Krausz, R. F., B. G. Young, et al. (2001). "Influence of weed competition and herbicides on 

glyphosate-resistant soybean (Glycine max)." Weed Technology 15: 530-534.

Loux, M., J. Stachler, et al. (2008). Weed Control Guide for Ohio Field Crops Ohio State 

University Extension.

Page 5-12
May, M. and R. Wilson (2006). Chapter 14: Weeds and Weed Control. Pgs. 359–386. Sugar 

Beet. A. P. Draycott. Oxford, United Kingdom, Blackwell Publishing Ltd. World Agricultural 

Series: 474 pgs.

Menalled, F. and M. Schonbeck (2013) Manage the Weed Seed Bank—Minimize "Deposits" and 

Maximize "Withdrawals". 

Mock, V. A., E. J. Creech, et al. (2011). Winter Annual Weeds and Soybean Cyst Nematode 

Management With a Guide for Identifying Known Weed Hosts, Purdue Extension. WS-36.

Monsanto (2012). "Early-Season Weed Competition in Corn."

Norsworthy, J. K., Ward, S. M., Shaw, D. R., Llewellyn, R. S., Nichols, R. L., Webster, T. M., 

Bradley, K. W., Frisvold, G., Powles, S. B., Burgos, N. R., Witt, W. W., and Barrett, M. (2012). 

"Reducing the Risks of Herbicide Resistance: Best Management Practices and 

Recommendations." Weed Science(Special issue): 31-62.

Penn State University (2009). "An Introduction to Weed Management for Conservation Tillage 

Systems."

PhysicalWeeding (2009). "Information: Integrated Weed Management." 

from http://physicalweeding.com/information/index.html.

Place, G. T., S. C. Reberg-Horton, et al. (2011). "Effects of soybean seed size on weed 

competition." Agronomy Journal 103: 175-181.

Prostko (2013) Soybeans Weed Control 2013 Georgia Soybean Production Guide 

Reddy, K. and J. Norsworthy (2010). Glyphosate-Resistant Crop Production Systems: Impact on 

Weed Species Shifts. Glyphosate Resistance in Crops and Weeds. Hoboken, NJ, John Wiley & 

Sons, Inc.: 213-233.

Renner, K. A. (2000) Weed Seedbank Dynamics. 4 

Page 5-13
Rosenberg, M. (2013). "Effect Of Weed Competition On Corn ".

Schonbeck, M. (2010). Know the Weeds, eXtension.com.

Shrestha, A., T. Lanini, et al. (2006). Conservation Tillage and Weed Management. Agriculture 

and Natural Sciences. University of California. 8200: 14.

Sikkema, P. H. and A. S. Hamill (2005). "Weed Costs Per Day: New Perspectives on Research 

into Early Weed Control."

Steckel, L. E., C. L. Sprague, et al. (2007). "Tillage, Cropping System, and Soil Depth Effects on 

Common Waterhemp (Amaranthus rudis) Seed-Bank Persistence." Weed Science 55(3): 235-

239.

University of California (2009). UC IPM Pest Management Guidelines: Corn. Oakland, CA, 

University of California Agriculture and Natural Resources, UC Statewide Integrated Pest 

Management Program: 42.

Weller, S., M. Owen, et al. (2010). Managing Glyphosate-resistant Weeds and Populations Shifts 

in Midwestern U.S. Cropping Systems. Glyphosate Resistance in Crops and Weeds. Hoboken, 

NJ, John Wiley & Sons, Inc.: 213-233.

Wilson, R., Ed. (1988). Biology of weed seeds in the soil. Weed Management in 

Agroecosystems: Ecological Approaches. Boca Raton, FL, CRC Press.

Page 5-14
Appendix 6. Herbicide Resistance

Page 6-1
Herbicide Resistance

Not unlike other agronomic practices, herbicide use may impart selection pressures on weed

communities, resulting in shifts in the weed community that favor those weeds that do not 

respond to the herbicide used (Owen, 2008). Herbicide resistance is described by the Weed 

Science Society of America as the “inherited ability of a plant to survive and reproduce 

following exposure to a dose of herbicide normally lethal to the wild type” (WSSA, 2011b). The 

shift to herbicide resistance in plants is largely a function of the natural selection of herbicideresistant traits and is strongly related to the repeated use of one or a limited number of herbicides 

(Durgan and Gunsolus, 2003; Duke, 2005).

Individual plants within a species can exhibit different responses to the same herbicide rate. 

Initially, herbicide rates are set to work effectively on the majority of the weed population under 

normal growing conditions. Genetic variability, including herbicide resistance, is exhibited 

naturally in normal weed populations, although at very low frequencies. When only one 

herbicide is used year after year as the primary means of weed control, the number of weeds 

resistant to that herbicide compared to those susceptible to the herbicide may change as the 

surviving resistant weeds reproduce. With no change in weed control strategies, in time, the 

weed population may be composed of more and more resistant weeds.

Both the increased selection pressure from the extensive use of glyphosate associated with 

glyphosate-tolerant crops along with the subsequent reduction in the use of other herbicides and 

changes in weed management practices (i.e., conservation tillage or no-till) have resulted in weed 

population shifts and increasing glyphosate resistance among some weed populations (Owen, 

2008; Duke and Powles, 2009). Glyphosate-resistant crops themselves do not influence weeds 

any more than non-transgenic crops. It is the weed control tactics chosen by growers that create 

selection pressure that ultimately over time changes these weed communities and may result in 

the selection of herbicide-resistant weeds (Owen, 2008).

History of Weed Resistance to Herbicides and its Development

One of the earliest selective chemical herbicides to be used in agriculture was 2,4-D, a synthetic 

auxin, whose commercial use began in 1945 (Burnisde, 1996). Use of 2,4-D in corn was 

successful in controlling broadleaf weeds such that in the mid-1950s 2,4-D was applied to nearly 

one-half of all U.S. corn acres (Knake, 1996). Within 12 years, the first herbicide resistance to 

2,4-D was reported in spreading dayflower in a Hawaiian sugarcane field (Commelina diffusa) in 

1957 (see report in (Sellers et al., 2011; Isaac et al., 2013)) and then in field bindweed 

(Convolvulus arvensis) in Kansas cropland in 1964 (Heap, 2013a). 

Simazine was the first triazine to be used commercially in 1956. In 1958, the herbicide atrazine 

was first registered for weed control in corn in the U.S. Similar to what had occurred with 2,4-D, 

triazines were used extensively in the 1960s and common groundsel resistant to triazine 

herbicides was discovered in Washington in 1970 (Buhler, unknown). Regardless of the

occurrence of resistant weeds, atrazine was, and still is, an extremely effective herbicide due to 

its broad spectrum, low cost, and flexible timing of applications (International, 2012). 

Page 6-2
ALS inhibitors or Group 2 herbicides were introduced in the mid-1980s and became extensively 

used in both corn and soybeans. With its broad-spectrum weed control, residual activity, and 

flexibility in application timing, the Group 2 herbicides became popular in the late 1980s and 

early 1990s. For example, by the early-1990s, PursuitTM, containing the ALS herbicide 

imazethapyr, was used on more than 75 percent of the soybeans in Iowa (Tranel and Wright, 

2002). The widespread use of Group 2 herbicides resulted in the rapid selection of ALS-resistant 

waterhemp. By the mid-1990s, Group 2 resistant waterhemp was so widespread that the industry 

essentially stopped recommending Group 2 herbicides for this weed (Hartzler, 2013). 

Sales of glyphosate began in 1974 and it became one of the most commercially successful and 

dominant herbicides in the U.S. (Duke and Powles, 2008). There are several reasons for the 

success of glyphosate in the market and the corresponding market sector penetration of 

glyphosate-tolerant crops since their introduction in the mid-late 1990s. Glyphosate: 1) works 

non-selectively on a wide range of plant species; 2) is a relatively low-cost herbicide; 3) 

enhances no-till farming practices; and 4) has minimal animal toxicological and environmental 

impact (Owen, 2008; Duke and Powles, 2009) (Duke and Powles, 2008). 

The widespread adoption of glyphosate-tolerant soybean, in combination with an increased 

reliance on glyphosate, has been related to the adoption of no-till cultivation which depends on 

controlling weeds without tillage. Glyphosate tolerant soybean also led to a simplification in 

weed control compared to past practices, reduced input and labor costs associated with the 

cultivar and glyphosate use, and increased flexibility in herbicide application timing (Lorenz et 

al., 2006).

Most instructive are the events leading to the development of glyphosate resistance in weeds in 

the U.S. The previous history of glyphosate use for 20 years did not result I the selection of 

herbicide resistant weeds. As a result, industry promoted the view that widespread glyphosate 

use was unlikely to result in the selection of glyphosate resistant weeds (Bradshaw et al., 1997),

despite the fact that resistance to other herbicides, such as 2,4-D were being reported (see 

history in (Mithila et al., 2011). The first case reported, glyphosate resistant rigid ryegrass, was 

documented and confirmed in Australia in 1996 (Powles et al., 1998), over twenty years after 

glyphosate first began to be used in agriculture. 

Herbicide-resistant crops were introduced in 1996 with glyphosate-resistant soybean rapidly 

adopted by growers. As glyphosate went off patent in 2000, increased usage of glyphosateresistant crops was facilitated by the low price of the herbicide. Tank mixes for separate activity 

against grasses and broad-leaf weeds were not needed when glyphosate could be used for weed 

control. In the mid-1990s, 51% of growers were using three, four or more herbicides for 

soybean weed control (cited in Gianessi et al. (2008)) or about three overall in 1995 (USDAERS, 1997). With the availability of glyphosate and glyphosate-resistant crops, herbicide 

applications could be reduced in many situations. 

The efficacy of post-applications of glyphosate became clear, with weed control often not 

requiring a pre-application for good control (Reddy, 2001). If a grower needed additional weed 

control for effectiveness or flexibility, a pre-application of glyphosate and a post-glyphosate 

application were as effective and cost less than a pre-application with a non-glyphosate residual 

herbicide followed by post-application of glyphosate (Reddy, 2001). Increasing glyphosate 

Page 6-3
applications resulted in a decline of the sales and use of most other herbicides. The earliest U.S.

glyphosate resistance in a GE crop was found in horseweed, Conyza canadensis, in Delaware 

soybean in 2000 (Heap, 2013a). Increasing exposure of weeds to glyphosate in other herbicide 

resistant crops such as corn and cotton soon began to expand the numbers and populations of 

resistant weeds in the U.S. 

The intense use of glyphosate compared to sparing use of other herbicides on field crops is 

apparent in overall herbicide use trends over the last decade, and surveys of grower usage, such 

as that of Prince et al. (2012), provide specific details (see also Figures 4-1, 4-3. 4-4, and 4-5). 

These surveys give evidence of the prevalent practices employed by growers in which 

glyphosate was nearly the only herbicide used with the subsequent overexposure of crops and 

weeds to glyphosate. In 2005, surveyed growers in multiple states rotating soybean and corn 

indicated they chose glyphosate 22% of the time for spring burndown, versus 9% for other 

herbicides (Table 6-1). For continuous soybean, growers chose glyphosate 46% of the time and 

22% another herbicide (Table 6-1) (Prince et al., 2012) . Overall, 74% of the continuous 

soybean growers used glyphosate two or more times during a growing season (Table 6-2), and 

growers rotating between corn and soybean, used glyphosate two or more times 50% of the time 

on soybean. When growers used non-glyphosate herbicides, continuous soybean growers used 

these herbicides in post-emergence applications 67% of the time, and corn/soybean growers 

applied the herbicides on soybean post-emergence 35% of the time (Table 6-2). Growers were 

choosing glyphosate frequently for pre-plant burndown, but also post-planting with high 

frequency, so that repeated exposure of weeds to glyphosate during crop production was 

common within the same season, and because the most common rotation crop for corn is 

soybean, exposure of weeds to selecting doses of glyphosate occurs in consecutive seasons. 

Prince et al. (2012) document that in 2005, glyphosate tolerant corn/glyphosate tolerant soybean 

rotations, only 9% of soybean acreage received non-glyphosate herbicides, although 45% of corn 

acreage received non-glyphosate treatment.

Table 6-1. Frequency of Spring Pre-plant Application of Glyphosate among Surveyed 

Growers (2005)

Herbicide Application

Crop Glyphosate Non-glyphosate

Continuous soybean 46% 22%

Soybean in soybean/corn 

rotation 22% 9%

Source: (Prince et al., 2012) 

Table 6-2. Frequency of Glyphosate Application to Crop by Surveyed Growers (2005).

Herbicide Application

Crop Glyphosate Non-glyphosate

Frequency 1X 2X 3X 1X 2X 3X

Continuous soybean 23 62 12 27 7 67

Soybean in soybean/corn rotation 48 47 3 53 12 35

Source: (Prince et al., 2012)

Page 6-4
It is clear that when herbicides are applied, selection for those weeds with adaptive mechanisms 

to escape elimination will survive. If the herbicide is repetitively used in crop production, the 

surviving weeds will be further selected, and dominant genes as well as multi-component 

resistance mechanisms will be selected. While many practices can be used to manage weeds, the 

recent history of glyphosate use shows that when the collective knowledge of resistance 

development is either neglected or practices not sufficiently integrated with mechanical and 

cultural controls, or with more robust herbicidal strategies, resistant weeds will arise. As noted 

earlier, it is not so much herbicide resistant crops that are a cause of herbicide resistant weeds, 

but from the failure to apply best management practices in the production of herbicide resistant 

crops.

Mechanisms of Herbicide Resistance in Weeds and Relationship to Selective Pressure

Two types of weed resistance may arise following inadvertent weed selection and both confer 

complex management concerns for growers. The first is target site specific resistance (TSR), 

and the second, non-target site specific (NTSR). The first results in an alteration of the target site 

of the herbicide so the target is no longer inhibited. The second type of resistance is more 

general and may confer resistance to a wide range of chemistries. For example, NTSR resistance 

may provide protection by reduced penetration of the herbicide, altered translocation, 

overproduction of targets, target mutation, or neutralization of cytoplasmic toxins (Délye et al., 

2013). TSR confers resistance usually to a single herbicide, and NTSR may confer resistance to 

as many as nine different modes of action (e.g., Lolium rigidum) and 16 herbicides (Burnet et al., 

1994). In the case of NTSR, the use of herbicides on weeds with unknown NTSRs may provide 

a substantial risk for development of weed resistance (Délye et al., 2013).

The target site alterations leading to TSR are often produced by dominant or semidominant 

nuclear mutations and can be found in herbicide Groups 1, 2, 3, 23, 14, and 9, while triazine 

herbicides (Group 5) result from dominant cytoplasmic mutations (Délye et al., 2013). This 

resistance arises following a single mutation, which because of its beneficial nature promotes 

immediate survival and is positively and rapidly selected within the agricultural environment. 

Glyphosate resistance that is TSR is a consequence of one amino acid change at position 106 of 

the chloroplast EPSPS protein. Worldwide, 14 of these populations have been identified 

(Beckie, 2011). 

Natural Tolerance 

Natural tolerance to certain herbicides may be apparent when weeds are first exposed to a 

herbicide, or with selection, existing genes may be selected and then accumulated to produce 

varying levels of tolerance (likely by NTSR). Field morning glory (Convolvulus arvensis L.) has 

such tolerance to glyphosate and has been assessed in detail (Westwood and Weller 1997). 

Glyphosate tolerance in Convolvulus was also found in historical populations which predated 

glyphosate resistant crop introductions (Baucon and Mauricio, 2010). The pre exposure NTSR

to glyphosate was at about the same level as that which is currently observed. Morning glory 

can also be shown to have pre-existing resistance (that is, by TSR) but which is not as high as 

that expressed by plants now collected (Baucon and Mauricio, 2010). Both types of resistance 

can exist in the species, but independently, with resource allocation costs apparent for the plant’s 

tolerance mechanisms for the herbicide (Baucon and Mauricio, 2008) . At least some 

Page 6-5
populations of 16 species have been alleged as not controllable by recommended field rates of 

glyphosate, presumably by natural tolerance mechanisms (Duke and Powles, 2008).

Weeds Resistant to Multiple Herbicides 

Direct resistance of a weed species to an herbicide is an unwelcome consequence of weed 

selection, but cross resistance to other herbicides in the same class or to other classes of 

herbicides provides an even greater consequence to those who manage weeds, since a grower’s 

choice of herbicide site of action (SOA) will be restricted in the present season’s crop and 

potentially also in the rotation crop. When resistance is based on non-target site mechanisms, 

which may include increased metabolism and reduced translocation to target sites, the weed may 

be capable of resistance to multiple herbicide modes of action (Beckie and Tardif, 2012). NTSR 

appears to arise from a weed’s accretion of variants of several genes which may originally have 

been subsets of stress-tolerance genes (see review in Délye (2013). Délye (2013) attributes 

much of the recently discovered weed resistance to this mechanism, and it is particularly 

important in Groups 9 (glyphosate) and 1 (acetyl-CoA carboxylase inhibitors), as well as grasses 

and probably broadleaf weeds (Group 2: acetohydroxyacid synthase inhibitors). In the case of 

glyphosate, Beckie (2011) lists 15 instances worldwide of glyphosate NTSR.

Weed Selection for Resistance to Herbicides by Overuse

The intense use of glyphosate on field crops compared to decreased use of other herbicides is a 

trend within the last decade, but how growers use glyphosate in field situations makes the 

situation clearer in grower surveys such as that of Prince (2012). These surveys give evidence of 

the prevalent practices employed by growers in which glyphosate is sometimes the only 

herbicide used, allowing the overexposure of crops and weeds to glyphosate. Growers were 

choosing glyphosate frequently for pre-plant burndown, but also post-planting with high 

frequency, so that repeated exposure of weeds to glyphosate during crop production was 

common within the same season. Because the most common rotation crop for corn is soybean, 

exposure of weeds to selecting doses of glyphosate occurs in consecutive seasons as well. 

Because conservation tillage systems are inherently more dependent upon weed management 

using herbicides, selective pressure on weeds is greater than that on fields using conventional 

tillage with its greater options for pre-plant primary tillage and post plant secondary tillage 

(Vencill et al., 2012). In a survey conducted in 2007, growers that planted 87% of their crops to 

glyphosate resistant corn, soy or cotton varied the SOA used on their crops ‘always’ or ‘mostly’ 

just 39% of the time, with the remaining 61% affirming they did so ‘seldom’ or ‘never’ (Frisvold

et al., 2009). Thus, when conservation tillage and HR crops define the production system, 

growers are likely to use the same herbicide (i.e., glyphosate) frequently. Some other options 

also may be foreclosed by conservation till (especially no-till), such as soil incorporation of 

residual herbicides, although some residuals can also be soil applied (Penn State Extention, 

2013). 

Considering the recommendations for success in reducing resistant weed development (Vencill

et al., 2012), unsuccessful herbicide strategies that have encouraged resistant weeds can include:

Page 6-6
1. Herbicide use of mostly one or a few modes of action (Norsworthy, 2012) and infrequent 

use of herbicide tank mixes, sequences and diversity across seasons (WSSA, 2011a), 

2. Incorrect timing of herbicide application (Norsworthy, 2012), 

3. Failure to consider the likelihood that a weed already has non-target site resistance 

mechanisms (Délye et al., 2013) against specific herbicides (including metabolic 

potential, ability to prevent translocation, or ability to sequester the herbicide).

4. Applying low doses of herbicide thereby allowing weeds to be exposed to low rates

herbicide which encourages sequential escapes and accumulating resistance genes

(WSSA, 2011b); 

5. Not establishing fields devoid of active weeds at planting or good weed control at canopy 

closure (for soybean) because not all available tools and herbicides were used (Monsanto, 

2013); resulting in poorer crop establishment and more weed initiation. 

Weed Resistance from Undervaluing a Balance of Residual and Contact Herbicides

The decrease in use of soil applied residual herbicides and a focus instead on mainly foliarapplied contact herbicides may be another basic and strategic misapplication of technology by 

field crop producers and these resulted in resistant weed development. In the era before 

introduction of HR soybean and corn, and afterwards, production changes by growers were noted 

in the use of herbicides in the transition to greater HR crop acreage. For soybeans, in 1996, 70% 

of growers used pre-emergent herbicides, but by 2002 they did so less than 20% of the time 

(Livingston and Osteen, 2012). A decline in corn pre-emergent herbicide use also occurred, 

from nearly 80% to around 60%. Post-emergent herbicides were applied to about 80% of 

soybean in 1996, then steadily increased to nearly 100% in 2010; in corn, post emergent 

herbicide use increased from 60% to 75%. These reflect increased use of glyphosate with its 

utility as an over the top and POST herbicide on soybean, but also a decline in reliance on preemergent non glyphosate herbicides. Likewise, Prince (2012) concluded that soybean growers 

were less likely than corn or cotton growers to use a residual herbicide (often pre-emergent) in 

their multistate survey of herbicide use in 2005 and 2010. Growers thus lost value from an 

herbicide by not deploying a residual (soil applied residual in no-till production) herbicide that 

has a different SOA than glyphosate, and relying on post-emergence control using glyphosate or 

another foliar active herbicide. Perhaps as a consequence of awareness of weed herbicide 

resistance or in an effort to combat glyphosate resistant crops, use of residual herbicides has 

increased modestly between 2005 and 2009 from 15% to 27% of soybean acreage (Owen et al., 

2011). 

Related to the issue of reductions in residual pesticide use is that of reductions in numbers of 

herbicides used in soybean and corn. An USDA Agricultural Resources and Environmental

Indicators (AREI) survey showed that soybean growers reached a high point of rotating

pesticides to slow resistance evolution in1998, but this declined steadily to low single digits in 

2010 (USDA-ERS, 2010). Corn growers chose to rotate pesticides to avoid resistance 

development from a high of 45% in 1998 to about 30% in 2010. Total applications of all 

herbicides have also declined from nearly 3 per year in soybean in 1996 to about 2 in 2006 

(USDA-ERS, 2010). Although this survey does not tabulate different sites of action applied in 

these years, it is clear that fewer SOAs were likely employed since overall application rates 

indicate limited actual use of non-glyphosate herbicides on soybean.

Page 6-7
Weeds Resistant to the Herbicides Commonly Used on Corn and Soybean.

As of March 21, 2013, internationally, there were 397 cases of herbicide resistant weeds in 217 

species (Heap, 2013a). The first herbicide-resistant biotypes were described in the 1950s, but the 

number of weeds resistant to herbicides increased dramatically in the 1980s and 1990s, and 

resistance to 21 of the 25 known herbicide sites of action has been identified throughout the 

world (Heap, 2013a). Of the 25 known herbicide sites of action, 11 of these sites of action are 

commonly used on corn and soy (See Appendix 4, Table 6-3). These sites of action and the 

particular herbicides commonly used to manage weeds in corn and soybean are listed on the top 

and bottom, respectively of Table 6-3. While there are hundreds of cases of herbicide resistant 

weeds, most of these weeds are not actively managed in corn and soybean. The analysis below 

focuses on weeds that are actively managed in corn and soybean fields and addresses which of 

these have developed herbicide resistance to the major herbicides used in corn and soybean.

Table 6-3, below, lists the problem weeds of corn and soybean, derived from survey data noted 

in Tables 5-1 and 5-2 in Appendix 5, and indicates whether validated herbicide resistance has 

been reported for these species as noted in the International Survey of Herbicide Resistant Weeds

(Heap, 2013a). Each column represents a different site of action and the WSSA number 

associated with that site of action is also listed on the top of each column. The major herbicides 

used on corn and soybean are listed below the table and color coded green if used on both corn 

and soybean, blue if used only on soybean, and yellow if only used on corn. If a particular weed 

has been reported to be resistant to any of the herbicides listed below the chart, the herbicide is 

so indicated for that combination and colored as just described. In cases where herbicide 

resistance has been noted only outside the U.S., the herbicide is marked with an asterisk. 

Quizalofop-p-ethyl is not among the top ten herbicides used in corn or soybean, but nevertheless 

is indicated where corn/soybean weeds are resistant. Cells are marked NR, for “not reported,” in 

cases where resistant weeds against the listed herbicides are not reported on International Survey 

of Herbicide Resistant Weeds site (Heap, 2013a).The last column lists those cases where weeds 

have been selected for resistance against more than one herbicide site of action corresponding to 

the listed herbicides. In those cases, the WSSA Herbicide Group # for the site of action is listed. 

For example, two types of multiply resistant kochia biotypes have been noted. One is multiply 

resistant to both ALS (#2) and PSII inhibitors (#5), the other is multiply resistant to ALS 

inhibitors (#2) and glyphosate (#9). 

Page 6-8
Table 6-3. Herbicide Resistant Biotypes of Problem Weeds in Corn and Soybean.

WSSA herbicide # 2 5 1 4 22 9 3 14 15 27 10

major weeds in 

corn and soybean

ALS PSII ACCase Auxin Bipyridiliums EPSPS DintroanilinesPPO Chloroacetamides 4-HPPD GS multiple

BROADLEAF

PIGWEED,REDROOT imazethapyr metribuzin1 N/A NR NR NR NR NR NR NR NR 2+5

Chlorimuronethylatrazine 2+7

chloransulammethylsimzine1

thifensulfuronmethyl

tribenuron 

methyl 1

nicosulfuron1

LAMBSQUARTERS

thifensulfuronmethylmetribuzin N/A dicamba1 NR NR NR NR NR NR NR NR

tribenuron 

methyl 1

atrazine

simzine

WATERHEMP

Chlorimuronethylatrazine N/A 2,4-D NR Glyphosate NR fomesafen NR mesotrione NR 2+5

imazethypyr lactofen isoxaflutole 2+14

chloransulammethyl2+9

thifensulfuronmethyl2+27

2+5+9

flumetsulam 2+5+14

nicosulfuron 2+9+14

rimsulfuron 2+5+27

2+9+27

2+5+14+27

2+5+9+14

2+5+9+27

2+5+9+14+27

COCKLEBUR imazethypyr NR N/A NR NR NR NR NR NR NR NR NR

Chlorimuronethyl

chloransulamPage 6-9
WSSA herbicide # 2 5 1 4 22 9 3 14 15 27 10

major weeds in 

corn and soybean

ALS PSII ACCase Auxin Bipyridiliums EPSPS DintroanilinesPPO Chloroacetamides 4-HPPD GS multiple

methyl

RAGWEED, GIANT

chloransulammethylNR N/A NR NR Glyphosate NR NR NR NR NR 2+9

imazethypyr

Chlorimuronethyl

KOCHIA imazethypyr atrazine N/A dicamba NR Glyphosate NR NR NR NR NR 2+5

thifensulfuronmethyl2+9

tribenuron 

methyl

rimsulfuron

nicosulfuron

Horseweed

Chlorimuronethylatrazine N/A NR paraquat Glyphosate NR NR NR NR NR 2+9

chloransulammethylsimzine 9+22

thifensulfuronmethyl5+71

tribenuron 

methyl

2+51

RAGWEED

Chlorimuronethylatrazine N/A NR NR Glyphosate NR flumioxazin NR NR NR 2+14

chloransulammethylsimzine fomesafen 2+9

imazethypyr lactofen

Field Bindweed NR NR N/A 2,4-D NR NR NR NR NR NR NR NR

SUNFLOWER

ChlorimuronethylNR N/A NR NR NR NR NR NR NR NR NR

imazethypyr

chloransulammethyl

flumetsulam

THISTLE, CANADA NR NR N/A 2,4-D1 NR NR NR NR NR NR NR NR

velvetleaf NR atrazine N/A NR NR NR NR NR NR NR NR NR

Page 6-10
WSSA herbicide # 2 5 1 4 22 9 3 14 15 27 10

major weeds in 

corn and soybean

ALS PSII ACCase Auxin Bipyridiliums EPSPS DintroanilinesPPO Chloroacetamides 4-HPPD GS multiple

dandelion NR NR N/A NR NR NR NR NR NR NR NR NR

HENBIT NR NR N/A N/A NR NR NR NR NR NR NR NR

Pennsylvania 

SMARTWEED

NR atrazine N/A NR NR NR NR NR NR NR NR NR

Russian thistle NR NR NR NR NR NR NR NR NR NR NR NR

Musk thistle 2,4-D

wild mustard

chloransulammethylatrazine1 N/A dicamba1 NR NR NR NR NR NR NR NR

imazethypyr metribuzin1 2,4-D1

thifensulfuronmethyl

tribenuron 

methyl1

black nightshade NR atrazine NR paraquat NR NR NR NR NR NR NR

simazine

mousear chickweed NR NR N/A NR NR NR NR NR NR NR NR NR

hemp sesbania NR NR N/A NR NR NR NR NR NR NR NR NR

palmer's amaranth imazethypyr atrazine Glyphosate mesotrione 2+9

Chlorimuronethyl2+5+27

thifensulfuronmethyl

sicklepod NR NR N/A NR NR NR NR NR NR NR NR NR

prickly sida NR NR NR NR NR NR NR NR NR NR NR NR

wild buckwheat

thifensulfuronmethylNR N/A NR NR NR NR NR NR NR NR NR

tribenuron 

methyl1

Grasses

foxtail, giant imazethypyr atrazine clethodim N/A NR NR NR NR NR NR NR NR

nicosulfuron quizalofopp-ethyl2

rimsulfuron

foxtail, yellow imazethypyr atrazine NR N/A NR NR NR NR NR NR NR NR

simzine

foxtail, green imazethypyr1 atrazine1 NR N/A NR NR NR NR NR NR NR NR

Page 6-11
WSSA herbicide # 2 5 1 4 22 9 3 14 15 27 10

major weeds in 

corn and soybean

ALS PSII ACCase Auxin Bipyridiliums EPSPS DintroanilinesPPO Chloroacetamides 4-HPPD GS multiple

johnsongrass

nicosulfuron NR quizalofopp-ethyl2N/A NR Glyphosate NR NR NR NR NR

NR

rimsulfuron1 clethodim

imazethypyr

crabgrass imazethypyr1 atrazine1 clethodim1 N/A NR NR NR NR NR NR NR NR

nicosulfuron1 quizalofopp-ethyl1

(

2

)

wheat, volunteer3 NR NR N/A N/A NR NR NR NR NR NR NR NR

quackgrass NR NR N/A N/A NR NR NR NR NR NR NR NR

barnyardgrass

imazethypyr1 atrazine quizalofoppethyl1

(

2

)

nicosulfuron1 simzine

oat, wild rimsulfuron1 NR clethodim1 N/A NR NR NR NR NR NR NR NR

quizalofopp-ethyl2

cupgrass, woolly NR NR N/A N/A NR NR NR NR NR NR NR NR

millet, wild-proso NR NR N/A N/A NR NR NR NR NR NR NR NR

sandbur NR NR N/A N/A NR NR NR NR NR NR NR NR

panicum, fall NR atrazine1 NR N/A NR NR NR NR NR NR NR NR

cheat4 NR NR N/A N/A NR NR NR NR NR NR NR NR

panicum, texas NR NR N/A N/A NR NR NR NR NR NR NR NR

sicklegrass NR NR N/A N/A NR NR NR NR NR NR NR NR

brome, downy NR atrazine1 clethodim N/A NR NR NR NR NR NR NR NR

simzine1 quizalofopp-ethyl2

brome, japanese4 NR NR N/A N/A NR NR NR NR NR NR NR NR

signalgrass, 

broadleaf

NR NR N/A N/A NR NR NR NR NR NR NR

NR

ryegrass (italian?) NR NR clethodim1 N/A NR Glyphosate NR NR NR NR glufosinate NR

quizalofopp-ethyl2

watergrass4 NR NR N/A N/A NR NR NR NR NR NR NR NR

bluegrass, annual NR simzine NR N/A NR Glyphosate NR NR NR NR NR NR

atrazine

Page 6-12
WSSA herbicide # 2 5 1 4 22 9 3 14 15 27 10

major weeds in 

corn and soybean

ALS PSII ACCase Auxin Bipyridiliums EPSPS DintroanilinesPPO Chloroacetamides 4-HPPD GS multiple

Key: Commonly used herbicides on corn and soybean

2 5 1 4 22 9 3 14 15 27 10

ALS PSII ACCase Auxin Bipyridiliums EPSPS Dintroanilines PPO Chloroacetamides 4-HPPD GS

Chlorimuron metribuzin clethodim 2,4-D paraquat Glyphosate pendimethalin flumioxazin metolachlor-S mesotrione glufosinate

imazethypyr atrazine quizalofop-p-ethyl2 dicamba fomesafen acetochlor isoxaflutole

chloransulam-methyl simzine clopyralid sulfentrazone

thifensulfuron-methyl saflufenacil

tribenuron methyl flutiacet-methyl

flumetsulam lactofen

thiencarbazonemethyl

rimsulfuron

nicosulfuron 1

outside US only

2

not a top 10 herbicide in either soy or corn

3

ALS resistant varieties through conventional breeding; glyphosate resistant variety identified as volunteers in a single Oregon field though never deregulated.

4

Not resistant to herbicides commonly used on corn and soybean

Source: (DAS, 2013; Heap, 2013b)

Page 6-13
The most widespread resistance is observed for the ALS inhibitors. Five different ALS inhibitors 

are commonly used on soybean and four are used on corn but none of these herbicides are 

commonly used on both crops. For this site of action, 12 of the 25 problem broadleaf weeds and 

7 of the 22 grasses include ALS resistant biotypes. We are not aware if these biotypes exhibit 

cross reactivity to other ALS herbicides listed or otherwise. From limited survey data, it has been 

inferred that ALS resistant weeds are present in all soybean fields in the Heartland (Tranel et al., 

2011).

Also widespread are biotypes resistant to PSII inhibitors which include 11 of the problem 

broadleaf weed species and eight of the grasses. Most of these cases involve biotypes that have 

been selected against atrazine in corn or metribuzin in soybean. 

ACCase inhibitors are grass specific herbicides and so have not been used on corn. They have 

been used on soybean and other crops. Clethodim is one of the more commonly used herbicides 

on soybean. Quizalofop-p-ethyl, is not commonly used on soybean but is considered here 

because EnlistTM corn would also be resistant to that herbicide. Seven of the problem grasses have 

developed resistance to quizalofop-p-ethyl and a subset of six biotypes are also reported to be 

resistant to clethodim, though for two of these cases, crabgrass, and barnyard grass, resistant 

biotypes have only been reported outside the U.S. 

Glyphosate, 2,4-D, and dicamba are the three herbicides that are commonly used on both 

soybean and corn. Of the three, only glyphosate is effective on most grass weeds. Relatively few 

grass weeds have resistant biotypes so glyphosate remains a very effective herbicide to control 

grasses. Of the problem weeds in corn and soybean, three: johnsongrass, Italian ryegrass, and 

annual bluegrass have been selected for glyphosate resistance. Glyphosate resistant broadleaf 

weeds have been more problematic. In this case, resistant biotypes have been selected in five 

broadleaf species and these resistant biotypes are more widely disseminated especially in the 

Southeast. The prevalence of such weeds is increasing and becoming more problematic in the 

Northern Crescent, Heartland, and Great Plains. Corn/soybean weeds that now have glyphosate 

resistance include waterhemp, giant ragweed, kochia, horseweed, and common ragweed.

Resistance to glufosinate offers an alternative mode of action to glyphosate for the broadspectrum control of weeds in soybean. To date, only Italian Ryegrass has been reported as 

resistant to glufosinate in the U.S. and this biotype is located in Oregon. However, this 

population of Italian Ryegrass also appears tolerant to glyphosate. Three problem corn/soybean 

weeds, lambsquarters, kochia, and wild mustard have dicamba resistant biotypes (though wild 

mustard is not reported to be resistant in the U.S.). Four problem corn/soybean weeds, 

waterhemp, field bindweed, canada thistle, and wild mustard, are reported to be resistant to 2,4-

D (though the Canada thistle and wild mustard biotypes are not reported to be resistant in the 

U.S.). Resistance to clopyralid, the other auxin commonly used in corn, has not been reported. 

For the other commonly used herbicides on corn and soybean, resistant biotypes have generally 

not been selected in the problem weeds. The exceptions include horseweed and black nightshade 

resistant to paraquat, waterhemp and ragweed resistant to PPO inhibitors, Italian ryegrass 

resistant to glufosinate, and waterhemp and Palmer’s amaranth resistant to the 4-HPPD inhibitors 

mesotrione and isoxaflutole. There are two sites of action for which we are not aware of any 

Page 6-14
resistant biotypes in the problem weeds. These include the dinitroanilines, such as 

pendamethalin, and the chloroacetamides such as metolachlor-S and acetochlor.

A number of the problem weeds have biotypes that are resistant to herbicides corresponding to 

more than one site of action. The most problematic is waterhemp which is resistant to six of the 

eleven sites of action commonly used in corn and soybean. Biotypes multiply resistant to 13 

combinations of these sites of action have been reported including one biotype that is resistant to 

five sites of action (Owen, 2012). Ragweed, kochia, and horseweed are each reported to have 

biotypes resistant to four sites of action including biotypes that are multiply resistant to two 

herbicides. Horseweed has four such biotypes, kochia and ragweed each have two. Multiply 

resistant biotypes have also been selected in redroot pigweed and giant ragweed. In total, 7 of the 

47 problem weeds include biotypes resistant to more than one herbicide.

References:

Baucon, Regina S., and Rodeny Mauricio. 2008. "Constraints on the Evolution of Tolerance to 

Herbicide in the Common Morning Glory: Resistance and Tolerance are Mutually 

Exclusive."

Baucon, Regina S., and Rodney Mauricio. 2010. "Defence against the herbicide 

RoundUp®predates its widespread use." Evolutionary Ecology Research 2010.12: 131-

41.

Beckie, HUgh. 2011. "Herbicide-resistant weed management: focus on glyphosate." SCI.

Beckie, HUgh, and Francois Tardif. 2012. "Herbicide cross resistance in weeds." Crop 

Protection 35 (2012) 15e28.

Bradshaw, Laura, Stephen Padgette, Steven Kimball, and Barbara Wells. 1997. "Perspectives on 

Glyphosate Reisitance." Weed Technology Review.

Buhler, Wayne. unknown. "Incidence and History of Herbicide Resistance." Resistance Pesticide 

Environmental Stewardship unknown. Web. December 5 

2013 http://pesticidestewardship.org/resistance/Herbicide/Pages/Incidence-and-Historyof-Herbicide-Resistance.aspx.

Burnisde, Orvin. 1996. "The History of 2,4-D and Its Impact on Development of the Discipline 

of Weed Science in the United States." Phenoxy Herbicides Chapter 2.

DAS.2013. "Supplemental Documentation in Support of Environmental Assessments in 

Response to Questions 4, 6-7 Received December 12, 2012 regarding DAS-40278-9 corn 

and DAS-68416-4 soybean. 2-4,D use

". Ed. Hoffman, Neil.

Délye, Christophe, Marie Jasieniuk, and Valérlie Le-Corre. 2013. "Deciphering the evolution of 

herbicide resistance in weeds."

Duke, S. 2005. "Taking stock of herbicide-resistant crops ten years after introduction." Pest 

Management Science 61: 211-18.

Duke, S.O., and S.B. Powles. 2009. "Glyphosate-resistant crops and weeds: Now and in the 

future." AgBioForum 12.3&4: 346-57.

Duke, S.O., and S.B. Powles. 2008. "Glyphosate: A once-in-a-century herbicide." Pest 

Management Science 64.4: 319-25. http://www.ncbi.nlm.nih.gov/pubmed/18273882.

Page 6-15
Durgan, B.R. , and J.L. Gunsolus. 2003."Developing Weed Management Strategies that Address 

Weed Species Shifts and Herbicide Resistant Weeds." 2011.August 14. 

Web. http://appliedweeds.cfans.umn.edu/pubs/03pub01.pdf.

Frisvold, George B., Terrance M. Hurley, and Paul D. Mitchell. 2009. "Adoption of best 

management practices to control weed resistance by corn, cotton, and soybean growers." 

AgBioForum 12: 370-81.

Gianessi, L.P. 2008. "Economic impacts of glyphosate-resistant crops." Pest Management 

Science 64.4: 346-52. http://www.ncbi.nlm.nih.gov/pubmed/18181242.

Hartzler, Bob. 2013."A History Lesson in Herbicide Resistance." Integrated Crop Management 

News. Web. http://www.extension.iastate.edu/CropNews/2013/0114hartzler.htm.

Heap, I. 2013a. "Herbicide Resistant Weeds in Soybean Globally: United States - State 

Specific." February 6, 2013 2013a. Web. February 25 

2013 http://www.weedscience.com/summary/Crop.aspx.

Heap, I. 2013b. "The International Survey of Herbicide Resistant Weeds." (2013b). Web. 

August, 2013 www.weedscience.com.

International, CropLife.2012. "Implementing Integrated Weed Management for Herbicide 

Tolerant Crops." Belgium: CropLife International. 

62. http://www.croplife.org/IntegratedWeedManagement.

Isaac, Wendy-Ann, Zongjun Gao, and Mei Li.2013 "Managing Commelina Species: Prospects 

and Limitations, Herbicides - Current Research and Case Studies in Use." Herbicides -

Current Research and Case Studies in Use. Ed. Price, Dr. Andrew. Vol.: InTech, 2013. 

Web http://www.intechopen.com/books/herbicides-current-research-and-case-studies-inuse/managing-commelina-species-prospects-and-limitations.

Knake, Ellery. 1996. "Phenoxy Herbicide Use in Field Corn, Soybean, Sorghum, and Peanut 

Production in the United States." Phenoxy Herbicides Chapter 6.

Livingston, M., and C. Osteen. 2012. "Agricultural Production Management. Pest Management 

": p.21-24.

Lorenz, Gus, Donald R. Johnson, Glenn Studebaker, Charles Allen, and Seth Young III. 2006. 

"Soybean Insect Management." University of Arkansas Division of Agriculture 

Cooperative Extension Service 2006. Web. September 9 

2011 http://www.aragriculture.org/insects/soybean/default.htm.

Mithila, J., J. Christopher Hall, William G. Johnson, Kevin B. Kelley, and Dean E. Riechers. 

2011. "Evolution of Resistance to Auxinic Herbicides: Historical Perspectives, 

Mechanisms of Resistance, and Implications for Broadleaf Weed Management in 

Agronomic Crops." BioOne.

Monsanto. 2013."Weed Resistance Risk Assessment: U.S.". Web. http://weedtool.com/.

Norsworthy, J.K., Ward, S. M., Shaw, D. R., Llewellyn, R. S., Nichols, R. L., Webster, T. M., 

Bradley, K. W., Frisvold, G., Powles, S. B., Burgos, N. R., Witt, W. W., and Barrett, M. 

2012. "Reducing the Risks of Herbicide Resistance: Best Management Practices and 

Recommendations." Weed Science.Special issue: 31-62.

Owen, M. D., B. G. Young, D. R. Shaw, R. G. Wilson, D. L. Jordan, P. M. Dixon, and S. C. 

Weller. 2011. "Benchmark study on glyphosate-resistant crop systems in the United 

States. Part 2: Perspectives." Pest Management Science 67.7: 747-

57. http://www.ncbi.nlm.nih.gov/pubmed/21452168.

Owen, M.D.K. 2008. "Weed species shifts in glyphosate-resistant crops." Pest Management 

Science 64.4: 377-87. http://www.ncbi.nlm.nih.gov/pubmed/18232055.

Page 6-16
Owen, Micheal D. K. 2012. "Assessment of herbicide resistance in 

Iowa." http://www.weeds.iastate.edu/mgmt/2012/resistancereport.html.

Penn State Extention. 2013. "Herbicides " 2013. 

Web http://extension.psu.edu/pests/weeds/control/introduction-to-weeds-andherbicides/herbicides.

Powles, Stephen, Debrah Lorraine-Colwill, James Dellow, and Christopher Preston. 1998. 

"Evolved resistance to glyphosate in rigid ryegrass (Lolium rigidum) in Australia."

Prince, Joby M., G. Shan, Wade Givens, M. D. Owen, S. C. Weller, B. Young, R. Wilson, and 

D. L. Jordan. 2012. "Benchmark Study: Survey of Grower Practices for Managing 

Glyphosate-Resistant Weed Populations." A Journal of the Weed Science Society of 

America.

Reddy, K.N.Weed Control and Yield Comparisons of Glyphosate-Resistant and GlufosinateResistant Corn Grown Continuously and in Rotation [Poster Abstract]. Southern Weed 

Science Society. 2001.

Sellers, B.A., J.A. Ferrell, and G.E. MacDonald. 2011."Herbicide Resistant Weeds." 

2011.August 14. Web. http://edis.ifas.ufl.edu/ag239.

Tranel, P.J., C.W. Riggins, M.S. Bell, and A.G. Hager. 2011. "Herbicide Resistances in 

Amaranthus tuberculatus: A Call for New Options." Journal of Agricultural and Food 

Chemistry 59: 5808-12.

Tranel, Patrick J., and Terry R. Wright. 2002. "Resistance of Weeds to ALS-Inhibiting 

Herbicides: What Have We Learned?" Weed Science 50.6: 700-

12. http://www.jstor.org/stable/4046642.

USDA-ERS. 1997 "Crop Residue Management." Agricultural Resources and Environmental 

Indicators 1996-1997. Eds. Anderson, M. and R Magleby. Washington: U.S. Department 

of Agriculture–Economic Research Service. 

356. http://www.ers.usda.gov/publications/arei/ah712/AH7124-2.PDF.

USDA-ERS. 2010. "Top 25 Agricultural Export Commodities, With Level of Processing, by 

Fiscal Year, Current Dollars." (2010). Web. August 

13 http://www.ers.usda.gov/Data/FATUS/#monthly.

Vencill, William K., Robert L. Nichols, Theodore M. Webster, John K. Soteres, Carol MallorySmith, Nilda R. Burgos, William G. Johnson, and Marilyn R. McClelland. 2012. 

"Herbicide Resistance: Toward an Understanding of Resistance Development and the 

Impact of Herbicide-Resistant Crops." Weed Science 60.sp1: 2-30.

WSSA.2011a "Lesson 5 - Principles of Managing Herbicide Resistance - " WSSA Lesson 

Modules: Herbicide Resistant Weeds. Vol.: Weed Science Society of America, 2011a. 24. 

Web http://wssa.net/wp-content/uploads/Lesson_5_HR-Turf.pptx.

WSSA. 2011b. "Weed Science Society of America." Weed Science Society of America April 18, 

2011 2011b. Web. May 25 2011 http://wssa.net/wp-content/uploads/WSSA-Mechanismof-Action.pdf.

Page 6-17
Appendix 7. Off-Target Pesticide Movement

Page 7-1
Off-Target Pesticide Movement

Once applied, pesticides (which include herbicides) that are not taken up by targeted plants that 

have been harvested will persist, degrade, or move in the environment. The potential 

environmental fate of an herbicide is shown in Figure 7-1. Degradation occurs by hydrolysis, 

photolysis, or microbial dissipation resulting in the herbicide being broken down and losing its 

herbicidal activity. Herbicides can be transported from their original application site by spray 

drift, runoff, leaching, volatility, wind erosion, or crop removal. Off-site movement of herbicides 

have the potential to impact non-target plant and animal communities living in proximity to 

fields in which herbicides are used, as well as human populations.

Figure 7-1. Environmental fate of herbicides in the environment.

Pesticide use has the potential to affect soil quality due to the impact to the soil microbial 

community. The length of persistence of herbicides in the environment depends on the 

concentration and rate of degradation by biotic and abiotic processes (Carpenter et al., 2002). 

Persistence is measured by the half-life or dissipation time (DT50), which equates to the length of 

time needed for the herbicide to degrade to half of its original concentration. 

Use of herbicides for field crop production may introduce these chemicals to water through spray 

drift, cleaning of pesticide application equipment, soil erosion, or filtration through soil to 

groundwater. Irrigation and rainfall occurring the first few days after herbicide application can 

influence herbicide loss through leaching and runoff. However, it has been estimated that even 

after heavy rains, herbicide losses to runoff generally do not exceed 5 to 10 percent of the total 

applied (USDA-NRCS, 2000; Tu et al., 2001). Planted vegetation, such as grass buffer strips, or 

crop residues can effectively reduce runoff (Fishel, 1997; USDA-NRCS, 2000). 

Pesticides applied to crops may volatilize, thereby introducing chemicals to the air. 

Volatilization typically occurs during application, but herbicide deposited on plants or soil can 

also volatilize. Volatilization occurs when pesticide surface residues change from a solid or 

Page 7-2
liquid to a gas or vapor after application. Volatilization refers to the transformation of a liquid or

solid pesticide into a gas. The extent of volatilization is dependent on properties of the chemical 

and herbicide formulation, and environmental factors such as air temperature, wind speed, and 

relative humidity. Volatilized pesticides can be carried by air currents potentially leading to offtarget exposure. Once airborne, volatilized pesticides may be carried long distances from the 

treatment location by air currents. The higher the vapor pressure of a chemical, the more 

volatility it exhibits. In addition, other physical and chemical pesticide properties, agricultural 

practices, meteorological conditions, persistence of a pesticide on plant surfaces, and soil 

properties influence the extent of volatilization (University of Missouri, 1997; US-EPA, 2012c). 

Most of the herbicides considered highly volatile are no longer used (Tu et al., 2001).

Drift is the physical movement of spray droplets moving off-site as a chemical application is 

made. Under certain conditions, the potential for physical drift from an application site to 

adjacent non-target environments is possible for all types of pesticide spray applications. This is 

an application- related phenomenon independent of the chemical pesticide, which may be

influenced by the formulation ingredients and spray mix additives. Spray drift is a concern for 

non-target susceptible plants growing adjacent to fields when herbicides are used in the 

production of any crop. This potential impact relates to exposure of non-target susceptible plants 

to the off-target herbicide drift (Jordan et al., 2009). Damage from spray drift typically occurs at 

field edges or at shelterbelts (i.e., windbreaks), but highly volatile herbicides may drift further 

into a field. The risk of off-target herbicide drift is recognized by EPA, which has incorporated 

both equipment and management restrictions to address drift on EPA-approved herbicide labels. 

These EPA label restrictions include requirements that the grower manage droplet size, control 

spray boom height above the crop canopy, restrict applications under certain wind speeds and 

environmental conditions, and use drift control agents (Jordan et al., 2009). 

The amount of drift varies widely and is influenced by a range of factors, including weather 

conditions, topography, the crop or area being sprayed, application equipment and methods, and 

practices followed by the applicator (US-EPA, 2000). EPA’s Office of Pesticide Programs 

(OPP), which regulates the use of pesticides and herbicides in the U.S., encourages pesticide 

applicators to use all feasible means available to minimize off-target drift. EPA-OPP has 

introduced several initiatives to help address and prevent the problems associated with drift. 

Currently, EPA-OPP is evaluating new regulations for pesticide drift labeling and the 

identification of BMPs to control such drift (US-EPA, 2009), as well as identifying scientific 

issues surrounding field volatility of conventional pesticides (US-EPA, 2010). Additionally, 

EPA-OPP and its Office of Research and Development are developing a new voluntary program, 

the Drift Reduction Technology (DRT) Program, which encourages the development, marketing,

and use of application technologies verified to significantly reduce spray drift (US-EPA, 2009).

EPA’s core pesticide risk assessment and regulatory processes ensure that protections are in 

place for all populations of non-target species potentially exposed to pesticides, including 

humans. These assessments provide EPA with information needed to develop label use 

restrictions for the pesticide. Growers are required to use pesticides, such as 2,4-D and 

quizalofop, consistent with the application instructions provided on the EPA-approved pesticide 

label. Labels can include restrictions related to minimizing drift or exclusion distances from 

bodies of water when necessary. These label restrictions carry the weight of law and are 

enforced by EPA and the states (FIFRA 7 USC 136j (a)(2)(G) Unlawful Acts). 

Page 7-3
In the comments to the EA on 2,4-D resistant corn and soybean, the issue was raised whether the 

increase in 2,4-D use expected from the adoption of EnlistTM corn and soybean would result in 

greater off-target effects to neighboring crops and thereby increase adverse socioeconomic 

impacts to these farmers. A group, Save Our Crops Coalition (SOCC), comprised of fruit and 

vegetable growers in the Heartland, petitioned the USDA to conduct an EIS regarding the 

deregulation of EnlistTM corn and soybean, because of their concern that off target movement of 

2,4-D would damage their crops. In this appendix, we consider the EPA’s regulation of off-target 

pesticide movement, the recorded cases of 2,4-D damages to neighboring farms, and the changes 

requested by DAS for the registration of EnlistTM products aimed at mitigating off-target 

pesticide movement.

2,4-D and off-target movement

Since it was introduced in 1948, there have been reports of 2,4-D adversely affecting non-target 

broadleaf food and feed crops, such as cotton, grapes and tomatoes, growing in the vicinity of 

target crops (Schultz et al., 1956). Such incidents have been linked to drift of spray droplets

(especially through aerial spraying) or drift of vapors formed by volatilization of the 2,4-D itself

(Dexter, 1993). 

Increased control of drift and volatilization across pesticides has been achieved with proper 

equipment setup and attention paid to climatic conditions at the time of application. University 

extension agencies have been especially prominent in developing and disseminating “Good 

Application Practices” to minimize drift. Additionally, pesticide label restrictions, state pesticide 

regulations, nozzle technology and manufacturer stewardship programs have helped to develop 

and establish application practices that minimize the potential for off-target exposure.

The herbicide 2,4-D is currently available in several formulations, including 2,4-D acid, 2,4-D

sodium salt, 2,4-D diethyl amine, 2,4-D dimethylamine salt, 2,4-D isopropyl acid, 2,4-D

triisopropyl acid, 2,4-D butoxyethyl ester), 2,4-D ethylhexyl ester, and 2,4-D isopropyl ester 

(US-EPA, 2005c). In 2011, EPA approved the first new use of the 2,4-D choline salt formulation

on crops, including corn and soybean (US-EPA, 2011). The 2,4-D mode of action as a synthetic 

auxin is not changed by these formulations, but the chemical and physical properties of each 

formulation influence the selection of equipment, mitigation measures adopted in the field to 

minimize off-target impacts, and formulation-specific safety measures. 2,4-D is formulated 

primarily as an amine salt in an aqueous solution or as an ester in an emulsifiable concentrate 

(US-EPA, 2005c). For a majority of uses, 2,4-D is combined with other herbicides because it 

economically enhances the weed control spectrum of many other herbicides such as glyphosate, 

dicamba, mecoprop, and acetolactate synthase (ALS)-inhibitor herbicides (US-EPA, 2005c).

Attributions of volatility to 2,4-D have largely been associated with the esters, particularly short 

chain esters. Early forms of 2,4-D included short chain esters that were favored due to rapid 

herbicidal activity, but these were relatively volatile (Nice et al., 2004). A desire to reduce risk of

off-target injury to sensitive crops, such as cotton, tomatoes or grapes, led to the development of

longer chain esters that were notably less volatile, and to development of various amine salts that 

EPA considers to be essentially non- volatile. The volatility of the salt forms approaches two 

orders of magnitude reduction compared to the short chain esters (US-EPA, 2013). In the last 

Page 7-4
two decades, longer chain esters have replaced the shorter chain esters and reduced volatility 

issues. In addition, the new 2,4-D choline salt further reduces the potential for volatility.

Federal and State Regulation of Off-target Pesticide Movement (DAS, 2013)

EPA is the federal agency vested with the authority and responsibility for regulating the sale, 

distribution and use of pesticides, including herbicides such as 2,4-D. EPA registers or approves 

a pesticide for one or more uses only after determining that the product will not cause 

unreasonable adverse effects on the environment – the statutory test for registration under 

FIFRA. When EPA approves the registration of a pesticide, it approves a particular product for a 

particular use or uses under specified conditions (including composition, application methods, 

usage rates, and protective measures) and specifies the language that must appear on the label of 

the pesticide product that sets forth those conditions and limitations. If a pesticide product is 

used in a manner that is inconsistent with its labeling, the user is subject to federal and state 

enforcement action. When making its registration decision, EPA specifies the data and 

information it needs to support that registration. Among the data EPA requires are those relating 

to off-target pesticide movement including, e.g., spray drift and volatilization (40 CFR part 158, 

Subparts L and N).

Federal law requires EPA to periodically review existing pesticide registrations to ensure that 

they meet the FIFRA standard for registration (the "no unreasonable adverse effects" criteria of 

FIFRA) under current scientific standards. EPA specifically addressed issues regarding off-site 

pesticide movement of 2,4-D in EPA’s 2005 Reregistration Eligibility Decision (RED) for 2,4-D 

(US-EPA, 2005c), which incorporated major label revisions to products containing 2,4-D. These

revisions included:

• lower limits for spray droplet size;

• prohibitions on spraying at wind speeds greater than 15 mph, 

• spraying with a wind direction that is not favorable to on-target deposition, or spraying

with sensitive non-target crops within 250 feet downwind;

• a prohibition on spraying at wind speeds of less than 3 mph if there are temperature 

inversion conditions, or stable atmospheric conditions at or below nozzle height;

• a prohibition on spraying where sensitive crops might otherwise be susceptible to drift;

• restrictions on boom length and spray release height for aerial applications, and nozzle 

height for ground boom applications;

• lower limits on application rates and total applications per year for specific crops

• compliance with any state and local laws that are more stringent (e.g., California, areas of 

which have seasonal limitations on use of 2,4-D) (US-EPA, 2005c)

EPA determined the use of the then-existing formulations of 2,4-D to be eligible for 

reregistration with those label restrictions. States also regulate the use of pesticides, including

Page 7-5
herbicides. A number of states have passed laws to specifically address spray drift (Feitshans, 

1999). These laws may include penalties and/or restrict application methods, require prior

notification, impose buffer zones, etc., as each state has deemed appropriate.

In addition to registering individual pesticides, EPA also regularly assesses the safety of pesticide

use more broadly, and has repeatedly addressed issues associated with off-target pesticide

movement. As stated on their web site 

(http://www.epa.gov/pesticides/factsheets/spraydrift.htm.) some of these efforts include:

• In 2009, EPA developed and issued for public comment a draft guidance document (PR 

Notice) on Pesticide Drift Labeling to provide guidance to pesticide manufacturers on 

labeling statements concerning pesticide drift, and to inform the public of EPA’s policies 

with regard to pesticide drift. EPA continues to work with stakeholders to finalize this 

guidance.

• For many years EPA has contributed funding to support education and training programs 

on drift management. EPA provides annual funds to states to support pesticide applicator 

training programs, many of which include educational material on drift management, and 

EPA has contributed to other educational programs, such as the National Coalition on 

Drift Minimization educational video and CD-Rom, the National Pesticide Applicator 

Certification Core Manual, and the National Agricultural Aviation Association’s 

Professional Aerial Applicator Support System (PAASS) to support their training and 

education programs to reduce drift incidents.

• EPA encourages pesticide applicators to use all feasible means available to them to 

minimize off-target drift. To support this goal, EPA has stated its intent to work with 

applicators, agricultural extension agents, registrants, environmental groups, and other 

interested stakeholders to collect and develop information on best management practices 

(BMPs) to reduce off-target drift for specific application methods and crop sector 

combinations. These guidance documents will be consolidated by EPA and made 

available online.

• OPP and the EPA’s Office of Research and Development are developing a new voluntary 

program, the Drift Reduction Technology (DRT) Program, which encourages the 

development, marketing, and use of application technologies, verified to significantly 

reduce spray drift (US-EPA, 2012a).

• EPA has also taken action to address issues around pesticide volatility. In December 

2009, EPA convened the FIFRA Scientific Advisory Panel (SAP) to examine scientific 

issues associated with field volatilization of conventional pesticides, focusing on 

methodologies by which bystander inhalation could be measured.

Existing precautions against off-target exposure (DAS, 2013)

Despite federal and state controls and the best efforts of applicators, off-target pesticide 

movement occasionally damages neighboring crops. Crops may be exposed to pesticide 

volatility or drift from a variety of sources, including public right of way uses for road 

Page 7-6
maintenance and utilities, and agricultural uses. Crops that have the potential for damage due to 

exposure to a particular pesticide are considered sensitive crops. Sensitive crops to 2,4-D include 

cotton, grapes, and many fruits and vegetables.

Growers use a number of approaches to protect their crops from off-target exposure. Location of

where the crop is grown is a key consideration; sensitive crop growers may choose to plant in 

fields that are sheltered or protected from potential exposure, and are not immediately adjacent to 

conventional crops(Mohr). Buffer zones and vegetative barriers are often used as a no spray

zone between a sensitive area and a crop being sprayed. A buffer zone may be a vegetative

barrier consisting of groves, hedge rows, wind breaks, pastures, or even the grower’s own 

conventional crops. Vegetation planted in strategic lines can reduce the extent of spray drift of

agricultural chemicals by filtering out spray droplets in air passing through their foliage 

(Department of Primary Industries). In some cases, growers are able to select a sensitive crop 

variety that is less sensitive to pesticides that are commonly applied to neighboring areas. 

Modified cultural practices, including timing of operations, are another approach that can be used

to protect against off-target exposure (Maynard et al., 2012).

Sensitive crop growers may help to avoid exposure in right of way areas by posting signs and 

making arrangements with government road crews or utility companies to do their own 

maintenance of easements and road ways near their sensitive crops. Similarly, neighboring farms 

can be notified of the presence of sensitive crops that require protection from herbicide spray

drift and volatility. Since applications of herbicides are increasingly being made by custom 

applicators, signage placed near field entrances alerting operators to the presence of sensitive

crops and that no sprays are allowed, are also used. Alternatively, sensitive crop growers may

notify the local coops and applicators directly. 

Some states have a pesticide sensitive crop registry and locator. Driftwatch (Driftwatch) is a 

national online tool for identifying specialty crop sites and to further enhance communications 

between producers of specialty crops and pesticide applicators that promote awareness and 

stewardship activities to help prevent and manage drift effects that sometime occur from spray 

operations. It currently includes the states of Colorado, Illinois, Indiana, Michigan, Minnesota, 

Missouri, Montana, Nebraska, and Wisconsin. This site features an easy-to-use Google MapsTM 

interface that clearly shows applicators the locations of registered areas so they can utilize the 

information in their ongoing stewardship activities before they spray. Other states, such as 

Maryland maintain their own, voluntary, pesticide-sensitive crop registry 

(http://mda.maryland.gov/Pages/homepage.aspx).

If crop damage occurs, affected growers can seek compensation by a variety of mechanisms. The

pesticide applicator may have insurance to cover such losses. In many cases, growers work out an 

equitable settlement. Where this is not possible, state pesticide enforcement bureaus are notified 

to view and document the damage. EPA obtains reports of pesticide incidents from private 

citizens, poison control centers, states, and other government and non-governmental 

organizations. In some states, the applicator may be subject to fines or other penalties (Feitshans, 

1999). The crop damage may also give rise to claims for legal damages in private lawsuits. 

Recorded Cases of Damages from Off-target Exposure to 2,4-D (DAS, 2013)

Page 7-7
USDA is not aware of a comprehensive, national database of offsite incidents from pesticide use.

Incidents involving alleged pesticide spray drift may be reported by various sources to the

grower, applicator, retailer, state or federal agency and/or the product manufacturer (US-EPA, 

2007). Information associated with the alleged incidents and investigations is managed by each 

respective party or entity.

Pesticide product registrants are required under FIFRA Section 6(a)(2) to submit certain types of

factual information to the U.S. Environmental Protection Agency (EPA) regarding adverse

effects on human health or the environment from the use of their registered products. If the 

incidents are “minor” they are included in the Aggregate Incidents Database and are not included 

in the Ecological Incident Information system (EIIS) (US-EPA, 2007). EIIS includes 

information on all ecological incidents reported to the agency prior to 1998 and all major 

incidents reported since. For plants, a major effect is one that is alleged to have occurred on more 

than 45% of the acreage exposed to the pesticide (US-EPA, 2005b). EIIS also includes 

information on incident reports submitted through other sources, such as the States, regardless if

they are "major" incidents or not. Incidents of adverse effects on lawns and other ornamentals 

caused by direct application of pesticide products are not entered into EIIS. When available, EIIS

includes date and location of incident, type and magnitude of effects observed in various species, 

use(s) of pesticides known or suspected of contributing to the incident. However, the database

contains a limited number of reported incidents and is not readily available to the public.

Registrants routinely submit reports on alleged incidents that have not been independently

verified. Thus, due to the nature of incidents and how they are typically reported through the

FIFRA 6(a)(2) process, the authenticity, validity, and/or accuracy of information contained in the

reports cannot be guaranteed by the registrants and may not accurately reflect actual incidents 

and products involved. In many cases there is not enough information to determine if the alleged 

adverse effects noted were in fact the result of pesticide spray drift and not another contributing 

factor. Thus, spray drift allegations may be reported as plant damage which may, in fact, have

been caused by diseases, insects, nutrient deficiencies, herbicide residue (carryover) and growing

conditions. For its part, EPA does not require reporting of adverse effects to non-target plants at 

the use site when the pesticide label provides adequate notice. As a result, some incidents may

not be reported because EPA is already aware of the potential for those effects to occur under 

certain conditions. It should be noted that none of the reports includes 2,4-D formulated with 

choline, a formulation designed to be less susceptible to drift, as the registration of this 

formulation was only recently approved by the EPA. 

While accurate, comprehensive, and reliable national data on offsite incidents from pesticide use

is not readily available, EPA’s Office of Pesticide Programs may publish incident data as part of 

its periodic review of all pesticides to ensure that their registrations continue to meet current 

scientific standards. Recently, EPA published a scoping document for 2,4-D acid, salts, and 

esters to support registration review that includes the results of a search of the EIIS and the

Aggregate Incident Reports databases for ecological incidents involving 2,4-D acid and its forms

(US-EPA, 2012a). They reported that, for all years, there were 422 incidents involving plants in 

the EIIS and 13,798 incident reports for all forms of 2,4-D in the Aggregate Incident Report 

database. From the details provided in the EPA summary of the EIIS reports, many of the plant 

incidents appeared to result from over-application of 2,4-D products to lawns or application of

2,4-D products to types of plants that are sensitive to 2,4-D. Other plant incidents were the result 

Page 7-8
of spray drift in agricultural settings. Detailed information was not provided for the Aggregate 

Incident reports. 

2,4-D use restrictions

EPA's registration for 2,4-D under section 3 of FIFRA includes certain restrictions on use that 

appear on the product's label, but EPA has not classified 2,4-D as a “restricted use pesticide”

(RUP). The most frequent means by which EPA addresses potential adverse effects is through 

warnings, prohibitions, restrictions and directions for use on the product label (40 CFR Part 156). 

When registering a product, the EPA also has the ability to classify a pesticide as a RUP should it 

deem that the product needs additional restrictions to decrease the risk of adverse effects (40 

CFR subpart I, 152.160). RUPs can only be applied by or under the direct supervision of an 

applicator certified by the state or EPA (DAS, 2013). 

After a pesticide is registered by EPA, states can register pesticides under specific state pesticide

registration laws. State lead agencies have primary authority for pesticides used within the state. 

In some cases, states may enact additional restrictions for use of a product to meet the uses and 

needs of their state. For example in Northeast Arkansas, rice, a crop where 2,4-D was used for 

weed control, and cotton, a 2,4-D sensitive crop, are grown in proximity. In 2006, the Arkansas 

State Plant Board (ASPB) received more than 100 complaints about 2,4-D drift (Bennett, 2006). 

The greater than usual drift was attributed in part to a very wet spring (USDA-NASS, 2006)

which resulted in many applications of 2,4-D being conducted aerially and done in a short period 

of time. The ASPB created a 2,4-D task force and a glyphosate task force in 2006 charged with 

the mission of developing proposed regulations for the board to consider (Bennett, 2007). After 

conducting public meetings and taking testimony from representatives from various agriculture 

sectors, the task forces submitted recommendations to the ASPB at the end of 2006. The final 

rule, adopted in February 2007, called for a ban on most aerial and ground spray applications of 

2,4-D in ten northeastern counties (area known as Crowley’s Ridge) between April 15 and 

September 15 and buffers of 2,4-D applications from susceptible crops in the remaining counties 

(Arkansas State Plant Board, 2007). Applications of glyphosate were limited to wind speeds no 

higher than 10 mph or 15 mph if using a commercially available hooded sprayer (Arkansas State 

Plant Board, 2007).

Currently, there are 18 states with some type of restriction on the use of 2,4-D (Figure 7-2 and 

Table 7-1). Types of use restrictions on registered products include general restricted use 

pesticide (RUP) regulations, formulation-specific restrictions, time-specific restrictions and/or

location-specific restrictions.

Types of State Restrictions

2,4-D products designated as a RUP – Four states, Massachusetts, New Jersey, New Mexico 

and Vermont have designated 2,4-D products a RUP. The RUP designation means that 

applicators must be certified to use the RUP product or have a licensed applicator within the

vicinity of the person making the application. The applicator must also keep spray records.

Page 7-9
Figure 7-2. States with restrictions on the use of 2,4-D

Source: (DAS, 2013).

Table 7-1. State 2,4-D Restrictions*

TYPE OF RESTRICTION STATE

State RUP designation, but with no spray/userestrictions (e.g. licensed 

applicators, permitting, record keeping, etc.)

MA, NJ, NM, VT

State RUP designation and spray/use restrictions CA, LA, TX, WA

No state RUP designation but spray/use restrictions 

 

AR, FL, ID, IA, MI, MS, 

NY, OH, OK, OR

Total number of states 18

*State regulations subject to change. 

Source: (DAS, 2013)

2,4-D products designated as a RUP along with spray use restrictions – Four states, 

California, Louisiana, Texas and Washington designate 2,4-D as a RUP and in addition impose 

spray use restrictions which vary by state. In these states, applications are restricted or

prohibited during certain times of the year (e.g. April through September) in designated counties. 

For the remaining counties in Louisiana and Texas, buffers from sensitive or susceptible crops 

are established.

2,4-D products are subject to specific spray use restrictions – Ten states, Arkansas, Idaho,

Iowa, Florida, Michigan, Mississippi, New York, Ohio, Oklahoma and Oregon impose spray use 

restrictions though they do not designate 2,4-D as a RUP. The restrictions range from buffers to 

aerial versus ground spray applications to the type of 2,4-D formulations which can be applied. 

For example, New York has spray use restrictions in only three counties. In these counties, no 

2,4-D can be applied within 100 feet of any grape vineyard and there is a 2-mile buffer for all 

Page 7-10
ester formulations. In Mississippi, 2,4-D is limited to ground spray applications only from April 

1 to September 30. In Iowa, ester formulations only are prohibited in five counties. The specific 

state restrictions of 2,4-D use are summarized in Table 7-2.

Table 7-2. Summary of State Restrictions on the Use of 2,4-D

STATE RUP RESTRICTIONS

Arkansas No

All 2,4-D herbicides are in Class F with use restrictions. From 

Apr. 15 - Sept. 15: 2,4-D use is not allowed in Clay, Greene,

Craighead, Poinsett, Cross, Crittenden, St. Francis, Lee, Phillips,

and Mississippi Counties. Permits may be obtained to allow

exemption with key requirements recording application details.

Buffer zone/wind speed requirements. Buffer zones set: e.g. 4

mile aerial; 1 mile ground. AR Regulations on Pesticide

Classification - Final Rule (Rev. 06/07):

California Yes

RUP for products 1 gal or greater containing over 15% active 

ingredient. Permits are needed to spray 2,4 - D in 

defined areas of Sacramento, Madera, Fresno, Kings, Tulare,

Kern, and San Joaquin Counties. Restrictions are based on dates, 

formulation type, wind speed, set-back from commercial

vineyard or cotton planting. 2,4-D use restrictions exist to

protect the California Red Legged Frog (buffer zones in 33

counties); 2,4-D salts and esters are designated as toxic air 

contaminants. Title 3, CCR 3, Sec. 6400

Florida No

Sale and use of highly volatile1 forms of organo-auxin 

herbicides is prohibited except for those products labeled as plant 

growth regulators on citrus. Minimum set-back distances from 

susceptible crops are specified based on wind speed. Max wind

speed = 10 mph. Applicator record keeping requirements are in 

effect. Aerial application by fixed-wing aircraft is prohibited Jan

1 until May 1 in Hendry, Palm Beach, Glades, Martin

counties.Florida Administrative Code Chapter 5E-2.033

( ff )

Idaho No

2,4-D ester restrictions exist in Latah, Nez Perce, and Clearwater 

Counties. Restrictions are based on aerial or ground application,

formulation type, set-back from susceptible crop, and wind

speed. Buffers from hazard areas required for 2,4-D amines and

acids, MCPA, MCPB, and dicamba. IDAPA 02.03.03 Sec. 550

Iowa No

The use of high volatile esters

2 formulations of 2,4-D and 2,4,5-

T, the alcohol fraction of which contains five or fewer carbons, is

prohibited in the counties of Harrison, Mills, Lee, Muscatine and

that part of Pottawattamie county west of Range 41 West of the

5th P.M. 21—45.27(206)

Louisiana Yes

2,4-D is designated an RUP for agricultural uses. Restrictions for

commercial and private applicators are based on timing, location, 

and wind speed. 32 parishes have restrictions. LA Title 7, Part

XXIII, § 1103

Page 7-11
STATE RUP RESTRICTIONS

Massachusetts Yes

If product contains >20% 2,4-D, it is a State RUP -- application

must be made by certified applicators and there are reporting

requirements. 333 CMR 1.00

Michigan No

No use of volatile ester forms of 2,4-D and MCPA are allowed 

within specified regions from May 1 to Oct. 1 in parts of Berrien,

Cass, Kalamazoo and Van Buren counties. There are sprayer

specifications for amine forms. MDA Reg 285.637

Mississippi No

For hormone-type herbicides,3 restrictions apply for aerial

application. Restrictions are based on date and type 

of aircraft and include no use of ester formulations, a 0.5 mile

set-back from cotton and susceptible crops, applications at wind

speed < 5 mph. There are applicator and licensing requirements.

Miss. Code Ann. § 69-21-109 (Part 3-Ch 10-Sub 01)

New Jersey Yes Concentrated 2,4-D (>20%) may only be purchased and used by

certified applicators N.J.A.C. 7:30-2.10

New Mexico

Yes

State restrictions apply to all 2,4-D products used in agriculture.

Spray restrictions in Curry and Roosevelt counties are based on 

timing, application method, and must be applied at windspreeds <

10 mph and only by certified applicators. Permits are required for 

applications of low volatile formulations. Esters and aerial

applications are not permitted in these 2 counties from Apr.15 to

Oct. 1. 21.17.56 NMAC

New York No

For 2,4-D, 2,4-5T, and MCP spray restrictions and set-backs of

100 ft from grape vineyards in portions of Chautauqua, Erie,

Niagara counties are in effect.

NY ECL Art. 33 § 321-324

Ohio No Restriction from use of ester formulation in Madison township of 

Lake County is in effect. ORC Title IX, Ch. 921

Oklahoma No

Applications of products containing 2,4-D esters or dicamba to

agricultural lands are prohibited in Greer, Harmon, and Kiowa

counties May 1-October 15; Applications of products containing

2,4-D, dicamba, picloram, triclopyr, or clopyralid are prohibited

in Jackson and Tillman counties May 1 - October. Notification

and reporting procedures are required for 2,4-D applications. 2

O.S. § 3-84 (35:30-17-24.1)

Oregon No

Use of high volatile esters of 2,4-D in areas of Morrow and 

Umatilla counties are prohibited Apr 1 - Sept 1 except by permit.

OAR 603-057-0301 to 0320

Page 7-12
STATE RUP RESTRICTIONS

Texas Yes

Use of 2,4-D, MCPA, dicamba, quinclorac is prohibited within 

4 miles of a susceptible crop in 53 "Pesticide Regulated

Herbicide Counties". No applications are permitted when wind 

speeds exceed 10 mph. Additional provisions are set county-bycounty. TAC 4-1-7-E §7.50, 53

Vermont Yes Class A restricted use, application requirements, and reporting 

requirments are in effect. 6 V.S.A. Ch 87

Washington Yes

All phenoxy hormone-type herbicides are restricted throughout 

eastern Washington with additional restrictions in 14 counties: 

Adams, Benton, Columbia, Douglas/Chelan, Franklin, Garfield, 

Grant, Kittitas, Klickitat, Lincoln, Okanogan, Spokane, Walla

Walla, Whitman, and Yakima. Specific restrictions are 

determined by county pertaining to boundaries; formulation type,

application parameters, dates, and aerial or ground, set-backs. 16

WAC 16-228,232

Source: (DAS, 2013)

1

All pesticides registered for sale in Arkansas are assigned to a Class. Each Class carries with it one or

more restrictions that must be complied with by the user, applicator, or dealer. The classification system

ranges from Class A which presumably all pesticides are registered as initially, until a problem develops. 

The only use-restrictions assigned to Class A products are those on the product label. If problems develop 

with a product, the Plant Board, after a public hearing, can move a product from the Class A designation 

to another designation (B, C, D, E or F) which has more restrictions. Each classification carries with it

all the restriction(s) that are specified for that class plus all that came before it. 

2Note: High volatility esters of 2,4-D are those that have five or fewer carbons on the alcohol side chain. 

Currently there are no high volatility esters registered for use in the United States.

3Hormone-type herbicides include 2,4-D, 2,4-DB, aminopyralid, clopyralid, dicamba, dichlorprop, 

fluroxypyr, MCPA, MCPB, mecoprop, picloram, quinclorac and triclopyr.

New technologies for controlling drift and volatility (DAS, 2013)

DAS conducted an extensive evaluation of various salts under conditions inducing high volatility 

to identify candidates that had significantly reduced volatility and thus lowered potential for 

injury to susceptible plants. The results led to the development of 2,4-D choline salt. This novel 

form of 2,4-D has been tested in the laboratory and subsequently in field studies. Quantification 

of volatilized 2,4-D from soybean and bare soil fields demonstrated that 2,4-D ethylhexylester

was the most volatile, with calculated loss rates of the 2,4-D ethylhexylester as much as two 

orders of magnitude greater than the 2,4-D dimethylamine (DMA) form, which is considered to 

be much less volatile than ester formulations (National Pesticide Information Center). The 

choline form of 2,4-D measured as much as 50X less volatility than the DMA form and had 

dramatically less injury to a variety of crops known to be sensitive to auxin herbicides under 

confined conditions as compared to ester and amine forms of 2,4-D (US-EPA, 2013).

Page 7-13
DAS’s new product containing 2,4-D choline and glyphosate DMA (Enlist DuoTM herbicide) will 

make the herbicide spray droplets larger and more uniform in size compared to a standard 2,4-D 

and glyphosate tank mix application. DAS has measured a 3X improvement (reduction) in 

driftable fines (<150 μ) for both 2,4-D choline and glyphosate under field conditions using 

commercial application equipment. This validates observations made under controlled laboratory 

and wind tunnel conditions. Coupled with using the latest in drift reduction nozzles, as much as a 

10X reduction in drift was achieved compared to a standard tank mix application of the same 

active ingredients using conventional nozzles.

Pending registration by EPA, DAS intends to market Enlist DuoTM Herbicide with Colex-D 

Technology, a pre-mix of the new 2,4-D choline salt and glyphosate dimethylamine with reduced 

drift and volatility characteristics, for use with EnlistTM corn and soybean. Via a Technology Use 

Agreement, DAS will require growers of EnlistTM corn and soybean who choose to use 2,4-D in 

post-plant applications to purchase the 2,4-D formulation in Enlist DuoTM to provide this added 

protection against off-target exposure. A combination of EPA-required label restrictions, 

contractual obligations and grower education and outreach are expected to minimize off-target 

effects to neighboring crops when applications of Enlist DuoTM is made to EnlistTM corn and

soybeans.

In addition to the technology innovations, the herbicide product label and product use guide do 

not allow applications into areas where temperature inversions are present, do not allow 

applications when winds exceed 15 mph, do not allow aerial applications, and require use of only

spray nozzles that produce a coarse or coarser spray droplet size. Such stewardship and 

responsible use requirements are expected to further minimize the potential for off-target 

herbicide movement.

In addition to the reduction of particle drift or volatilization due to physical properties of the 

herbicide formulation, other precautions have been included in conjunction with the EnlistTM

Weed Control System to minimize the potential for off-target movement. Specifically, DAS will 

request an amendment to its pending herbicide label submitted to EPA to include language 

regarding sensitive crops under a new “Susceptible Plants” heading on the label and label 

language requiring buffer zones between areas of 2,4-D choline use and sensitive plants 

(Coalition, 2012). The proposed label for Enlist DuoTM Herbicide with Colex-D TechnologyTM

label does not allow herbicide application through any type of irrigation equipment and 

prohibits aerial application (DAS, 2011). Individual state regulations for use of 2,4-D, such as 

the widespread prohibition of aerial application and restricted seasonal application, will also 

remain in effect. For instance, Texas has limited the application of “regulated herbicides” (such 

as 2,4-D) by county with the aerial application of 2,4-D being prohibited in many counties 

between March 10 and September 15 or outright prohibited within a given distance of any 

susceptible crop (4 Tex. Admin. Code §7.53). Iowa state law prohibits the use of some 2,4-D 

esters in some counties (21 IAC 45.27 [2013]). Mississippi prohibits the aerial application of 

2,4-D by fixed wing aircraft between April 1 and September 30 (CMSR 02-001-310). However, 

Mississippi allows 2,4-D to be applied by helicopter between April 1 and September 30 as long 

as certain application criteria are met, such as the use of precision spray systems, the use of 

booms no longer than rotor diameter, a flight speed of no more than 30 mph during application, 

and wind speed of 5 mph or less at the time of application (CMSR 02-001-310).

Page 7-14
Use of the innovative choline salt of 2,4-D, the new formulation technologies, and Dow 

AgroSciences’ Stewardship Program is expected to help reduce the potential for off-target 

impacts on sensitive crops and non-crop plants/organisms. 

Proposed Herbicide Label Language for Enlist DuoTM (DAS, 2013)

DAS has submitted to EPA for approval a proposed label for its Enlist DuoTM herbicide with 

Colex-D Technology

TM, a pre-mix of the new 2,4-D choline salt and glyphosate DMA. DAS’s

proposed label contains the instructions for use directly addressing the potential for spray drift 

and volatility. The same label instructions will be submitted for use on EnlistTM soybeans.

DAS has submitted for EPA approval the following proposed Enlist DuoTM label language

specifically addressing spray drift management. During its label approval process, EPA may

impose additional use restrictions or other protective measures for corn and/or soybean.

Spray Drift Management

Avoid drift. Use extreme care when applying this product to prevent injury to desirable plants 

and crops.

Do not allow GF-2726 to mist, drip, drift or splash onto desirable vegetation since minute 

quantities of this product can cause severe damage or destruction to the crop, plants or other

areas on which treatment was not intended. The likelihood of injury occurring from the use of

this product increases when winds are gusty, as wind velocity increases, when wind direction is 

constantly changing or when there are other meteorological conditions that favor spray drift. 

When spraying, avoid combinations of pressure and nozzle type that will result in fine particles 

(mist) which are likely to drift. Do not apply at excessive speed or pressure. Use of this 

product in any manner not consistent with this label may result in injury to persons, animals or

crops, or other unintended consequences.

Avoiding spray drift at the application site is the responsibility of the applicator. The interaction 

of many equipment- and-weather-related factors determines the potential for spray drift. The

applicator and the grower are responsible for considering all these factors when making

decisions.

Do not aerially apply this product. 

Droplet Size

Apply as a coarse or very coarse spray (ASABE S-572 Standard). Use drift reducing nozzle tips 

in accordance with manufacturer directions that produce a droplet classification of coarse or very

coarse to significantly reduce the potential for drift.

Groundboom Application

Use the minimum boom height based upon the nozzle manufacturer’s directions. Spray drift 

potential increases as boom height increases. Spray drift can be minimized if nozzle height is not 

greater than the maximum height specified by the nozzle manufacturer for the nozzle selected.

Page 7-15
Wind

Drift potential is lowest at wind speeds of 10 mph or less. However, many factors, including

droplet size and equipment type, determine drift potential at any given speed. Do not apply at 

wind speeds greater than 15 mph. Note: Local terrain can influence wind patterns. The

applicator should be familiar with local wind patterns and how they affect drift.

Temperature and Humidity

When making applications in low relative humidity, set up equipment to produce larger droplets 

to compensate for evaporation. Droplet evaporation is most severe when conditions are both hot 

and dry.

Temperature Inversions

If applying at wind speeds less than 3 mph, the applicator must determine if: a) conditions of

temperature inversion exist, or b) stable atmospheric conditions exist at or below nozzle height. 

Do not make applications during a temperature inversion or stable atmospheric conditions. 

Temperature inversions restrict vertical air mixing, which causes small suspended droplets to 

remain in a concentrated cloud. This cloud can move in unpredictable directions due to the light 

variable winds common during inversions. Temperature inversions are characterized by

increasing temperatures with altitude and are common on nights with limited cloud cover and 

light to no wind. They begin to form as the sun sets and often continue into the morning. Their

presence can be indicated by ground fog; however, if fog is not present, the presence of an 

inversion can also be identified by the movement of smoke from a ground source. Smoke that 

layers and moves laterally in a connected cloud (under low wind conditions) indicates an 

inversion, while smoke that moves upwards and rapidly dissipates indicates good vertical air 

mixing.

Drift Setbacks from Sensitive Areas

Allow setbacks (buffer zones) upwind of sensitive area (e.g., residential areas, bodies of water, 

known habitat for threatened or endangered species, sensitive non-target crops other than those

listed above).

If a coarse or very coarse droplet classification cannot be maintained, an upwind setback of 250 

feet from sensitive areas must be observed.

Applicators will not exceed a spray volume of 15 gallons (water) per acre. 

In addition, when sensitive areas are nearby, applicators will use recommended drift setbacks 

based on wind speed and spray boom height above canopy (see below). 

Page 7-16
Table 7-3. Drift Setback Distances (feet)

Susceptible Plants

Do not apply under circumstances where spray drift may occur to food, forage, or other plantings 

that might be damaged or crops thereof rendered unfit for sale, use or consumption. Avoid 

contact of herbicide with foliage, green stems, exposed non-woody roots of crops, desirable

plants and trees because severe injury or destruction may result. Small amounts of spray drift that 

may not be visible may injure susceptible broadleaf plants. Before making an application, please

refer to your state’s sensitive crop registry (if available) to identify any commercial specialty or

certified organic crops that may be located nearby.

Commercially grown tomatoes and other fruiting vegetables (EPA crop group 8), cucurbits (EPA

crop group 9), and grapes are particularly sensitive to drift from this product. Do not apply when 

wind direction favors off-target movement onto these crops.

State and Local Requirements

Applicators must follow all state and local pesticide drift requirements regarding application of

2,4-D herbicides. Where states have more stringent regulations, they must be observed.

The submitted Enlist DuoTM label language also requires additional measures to avoid off- target 

movement and crop injury, including detailed instructions for clean-out of sprayer equipment, 

use of drift control additives, and boom and nozzle height instructions.

Additional DAS measures to address spray drift and volatility

As noted above, DAS will contractually require growers of EnlistTM corn and soybean who wish 

to use 2,4-D as an in-crop herbicide to use only Enlist DuoTM. This new 2,4-D technology will 

provide substantially lower volatility than any other form of 2,4-D, as well as improved drift 

control, low odor, and improved handling characteristics.

Through its Technology Use Agreement, DAS will impose a legal and contractual obligation that 

will require all growers of EnlistTM corn and soybean to:

Wind Speed 

(mph)

Spray 

Boom <24 

inches 

above 

Canopy

Spray 

Boom >24 

inches 

above 

Canopy

<5 15 `30

5 – 10 40 80

10 – 15 80 150

Page 7-17
Use only EPA accepted and DAS authorized 2,4-D formulations containing Colex-D 

Technology

TM, such as Enlist DuoTM, for in-crop applications to EnlistTM corn and soybean.

Read and follow FIFRA Pesticide Product Label directions.

Read and follow the EnlistTM Weed Control System Product Use Guide.

Use properly maintained and calibrated ground application equipment for Enlist DuoTM

with Colex-D TechnologyTM with minimum boom heights.

Use nozzles that reduce the potential for physical drift of Enlist DuoTM with Colex-D 

TechnologyTM.

Follow instructions for equipment clean-out after product use.

DAS will provide comprehensive training on its technology and portfolio of products to growers, 

dealers and distributors through a variety of formats. Education and training, reinforced through 

product profiles, technical bulletins, sales literature, direct mailing and websites will also be 

presented in multiple formats to enhance learning and mastery of core concepts related to 

stewardship to be employed around EnlistTM corn and soybean. A variety of educational formats 

will be used to promote concept learning. This training will include education on spray

technology and herbicide application, including spray quality basics, as well as spray quality of

Enlist DuoTM, as well as how to minimize the potential for off-target movement of Enlist DuoTM.

Producers who do not comply with the requirements of the stewardship program risk losing 

access to the EnlistTM Weed Control System. Legal penalties may also be imposed by state 

regulatory agencies when label instructions are not followed.

Potential Off-target Pesticide Impacts on Organic Crops (DAS, 2013)

Growers of organic crops may also face economic damages from off-target pesticide movement, 

even if their crops are not damaged. If a certifying agent tests a crop grown under organic 

production and the test reveals the presence of residues from a pesticide not approved for use 

under the National Organic Program (NOP), the crop may not be sold as organic if the residue is 

present at a level greater than five percent of the EPA tolerance for the detected prohibited 

residue (7 CFR 205.671). A grower whose organic crops were subject to off-target pesticide 

movement that resulted in residue levels greater than five percent of the EPA tolerance could 

then lose the organic premium he may otherwise have obtained for his crop. While some 

certifying agents have refused to allow organic production on fields that have been the objects of 

spray drift, a recent court decision found this three year ban on organic production following 

spray drift to be inconsistent with the NOP (Anonymous, 2012).

In finalizing the NOP, USDA described the following in regards to grower’s responsibilities to 

protect against chemical drift (65 FR 80556):

Drift has been a difficult issue for organic producers from the beginning. Organic operations 

have always had to worry about the potential for drift from neighboring operations, particularly 

Page 7-18
drift of synthetic chemical pesticides. As the number of organic farms increases, so does the 

potential for conflict between organic and nonorganic operations.

It has always been the responsibility of organic operations to manage potential contact of organic

products with other substances not approved for use in organic production systems, whether from 

the nonorganic portion of a split operation or from neighboring farms. The organic system plan 

must outline steps that an organic operation will take to avoid this kind of unintentional contact.

When we are considering drift issues, it is particularly important to remember that organic 

standards are process based. Certifying agents attest to the ability of organic operations to follow 

a set of production standards and practices that meet the requirements of the Act and the 

regulations.

All of the preventions discussed above are available to organic growers and many are required by

the NOP as part of their organic production plan. Similarly, insurance and legal recourse may be

available to organic growers who lose premiums as a result of spray drift. 

2,4-D has an extensive history of safe and effective use. It has been thoroughly reviewed and 

reregistered by all major regulatory agencies in the world within the last ten years. Recently 

(April 2012), the EPA denied a petition to cancel the tolerances and registrations for 2,4-D based 

on toxicological hazard. The Agency issued a denial of that petition, affirming that 2,4-D posed 

no unreasonable risk when used as directed (US-EPA, 2012b). Therefore the impacts to the 

physical environment are expected to be similar under the No Action and Action Alternatives.

Other potential sources of off-target movement (DAS, 2012b)

Soil Leaching

2,4-D has a relatively short half-life and is rather immobile in the soil. In 35 recent field 

dissipation studies across the U.S., less than 5% of applied 2,4-D moved downward more than 15 

cm (6 inches). The average lowest depth detected ranged from 6 to 12 inches in soils of the 

southern United States, and 16 to 24 inches in low organic soils where greater movement would 

be expected ((Industry Task Force, 2006) cited in (DAS, 2012a)). Groundwater detections of

2,4-D, which are very rare, are largely attributed to direct introduction by misuse or spills at well 

sites ((Industry Task Force II, 2013)cited in (DAS, 2012a)). Proper application and avoiding 

filling spray equipment near well heads are standard good farming practices that minimize the

potential for leaching and work effectively for 2,4-D.

Runoff

The environmental risks of pesticide use are assessed by EPA in the pesticide registration 

process and are regularly reevaluated by EPA for each pesticide to maintain its registered status 

under FIFRA. EPA’s process ensures that each registered pesticide continues to meet the highest 

standards of safety to protect human health and the environment (DAS, 2012a).

Both field crop and aquatic application for weed control are registered uses of 2,4-D (US-EPA, 

2005c). Glyphosate is registered for use on many food and non-food field crops as well as noncrop areas where total vegetation control is desired (US-EPA, 1993). Although the registered 

Page 7-19
use of glufosinate is primarily terrestrial (US-EPA, 2008; Bayer CropScience, 2011), it may be 

applied to certain confined waters for irrigated crops, such as rice (US-EPA, 2002). 

As described in (DAS, 2012a), as part of an ecological risk assessment, EPA recently evaluated 

monitoring data from the USGS NAWQA program to assess the current trend of 2,4-D 

concentrations in surface water and groundwater (US-EPA, 2013)). 2,4-D was detected in 47

percent of surface water samples (i.e., 434 samples from a total national dataset of 931 samples). 

The maximum concentrations of 2,4-D ranged from 0.008 μg/l to 8.7 μg/L. 2,4-D was detected 

in only 1 percent of the groundwater samples (i.e., 12 samples from a total national dataset of 

1,184 samples). The maximum concentrations of 2,4-D ranged from 0.008 μg/L to 1.4 μg/L. 

The reported concentrations for both surface water and groundwater are lower than in the 

previously reported drinking water memorandum (US-EPA, 2004). 

As described in (DAS, 2012a), 2,4-D is currently approved by EPA for aquatic applications to 

control aquatic weeds in food use areas (i.e., rice and fish farms) as well as industrial areas (i.e., 

drainage systems) (US-EPA, 2005c). When used for aquatic treatments (direct application to 

water for aquatic vegetation control), 2,4-D has a half-life of between 3.2 days and 27.8 days 

(US-EPA, 2005c); the half-life of 2,4-D in aerobic aquatic environments is approximately 45 

days, and the half-life of 2,4-D esters in normal agricultural soil and natural waters is less than 3 

days (US-EPA, 2005a; US-EPA, 2009). EPA has stated that the 2,4-D acid and amine salts are 

practically non-toxic to freshwater or marine fish (US-EPA, 2005c). 

Environmental Loading of Herbicides Used on Corn (DAS, 2012b)

DAS has conducted an analysis to determine the anticipated impact on environmental loading of 

herbicides resulting from the use of 2,4-D choline on herbicide tolerant DAS-40278-9 corn,

DAS-68416-4, soybean, and DAS 44406-6 soybean. Specifically, this analysis looked at the

environmental load of herbicides applied on glyphosate tolerant corn and soybeans to control 

glyphosate resistant and hard-to-control weed biotypes (DAS, 2012a). The top currently

available herbicide programs (excluding just increasing the rate of glyphosate alone) that are

currently being recommended to control glyphosate resistant weeds in corn under scenarios 

representative of different key corn-growing regions were compared to projected use of Enlist 

DuoTM. While the range of rates of these currently available alternate programs and the ones for 

Enlist DuoTM programs overlapped, when the average of the Enlist DuoTM program rates were

compared to the average of all of these top alternates, the analysis indicated that the use of 2,4-D 

on herbicide tolerant DAS-40278-9 corn would reduce the per acre environmental load of 

herbicides compared to these top, currently available, non-glyphosate alternative programs. 

Reductions on corn ranged by 0.15 to 0.74 lb ai/ac, within the individual scenarios, with an 

overall average reduction of 0.49 lb ai/ac across all scenarios (DAS, 2012a).

Herbicide use may increase to meet the need for additional integrated weed management tactics 

to mitigate herbicide-resistant weeds in different cropping systems (Culpepper et al., 2008; 

Owen, 2008; Heap, 2011; Owen et al., 2011). Some of these adjustments may have the potential 

to impact surface water quality through increased sedimentation and agricultural chemical 

loading derived from exposed soils (Towery and Werblow, 2010; Owen et al., 2011). Some of 

these adjustments have the potential to impact air quality by increased emissions from tillage 

equipment and release of particulate matter generated from soil disturbance during tillage 

operations (Madden et al., 2009). Increases in herbicide resistant weeds potentially could lead to 

Page 7-20
a decline in no-till and conservation tillage. Declines in such practices are expected to reduce air 

quality from greater use of heavy field equipment and greater release of airborne particles.

Implementation of BMP to slow soil erosion and filter pollutants from surface runoff, such as 

vegetated strips, control of spray drift, and adherence to label restrictions governing safe 

application and equipment cleanup, minimize the potential for pesticide impacts to surface and 

groundwater.

The environmental risks of pesticide use are assessed by EPA in the pesticide registration 

process and are regularly reevaluated by EPA for each pesticide to maintain its registered status 

under FIFRA. In this process, steps to reduce pesticide drift and volatilization are included on a 

pesticide’s label approved by EPA. EPA’s process ensures that each registered pesticide 

continues to meet the highest standards of safety to protect human health and the environment. 

Use of the herbicides glyphosate 2,4-D, and glufosinate would be contingent upon periodic 

reevaluation and continued approval by EPA.

References:

Johnson v. Paynesville Farmers Union Cooperative Oil Company. State of Minnesota Supreme 

Court 2012.

Arkansas State Plant Board.2007. "Final Rule Arkansas Regulations of Pesticide Classification 

". http://www.sos.arkansas.gov/rulesRegs/Arkansas%20Register/2007/jul_2007/209.02.0

7-005.pdf.

Bayer CropScience. 2011. "Ingite 280 SL Herbicide Label 5a " Bayer CropScience 2011. Web. 

September 28 2011 http://fs1.agrian.com/pdfs/Ignite_280_SL_Herbicide_Label5a.pdf.

Bennett, D. 2006. "2,4-D Damages Arkansas Cotton." Delta Farm 

Press. http://deltafarmpress.com/24-d-damages-arkansas-cotton.

Bennett, D. 2007. "Proposed Regulations Target Arkansas 2,4-D and glyphosate drift." Delta 

Farm Press.

Carpenter, Janet, Allan Felsot, Timothy Goode, Michael Hammig, David Onstad, and Sujatha 

Sankula. 2002."Comparative Environmental Impacts of Biotechnology-derived and 

Traditional Soybean, Corn, and Cotton Crops." 2011.July 8. Web. www.cast-science.org.

Coalition. 2012. "JOINT STATEMENT OF DOW AGROSCIENCES AND THE SAVE OUR 

CROPS COALITION REGARDING 2,4D TOLERANT CROPS AND THE 2,4D 

CHOLINE SALT HERBICIDE."

Culpepper, A. S., J.R. Whitaker, A.W. MacRae, and A.C. York. 2008. "Distribution of 

Glyphosate-Resistant Palmer Amaranth (Amaranthus palmeri) in Georgia and North 

Carolina During 2005 and 2006." Journal of Cotton Science 12.306-310.

DAS.2012a. "DAS Comments to APHIS-2012-0019 on EA for DAS-68416-4 Soybean parts 2a, 

2b, 2c, and 3."

DAS.2012b. "DAS comments to APHIS-2012-0019. Stewardship. Herbicide volume estimate on 

soybean. off target exposure. trait stacking. 2,4-D toxicity evaluation. analysis for the 

presence of dioxins and furans. errata. non ge soybean. regulatory status of herbicides 

that may be used on enlist soybean, 2,4-D choline formulation, lack of toxicological or 

biological synergistic effects between glyphosate and 2,4-D, auxin resistant waterhemp, 

impact of enlist on herbicide use."

DAS.2011. "EnlistTM Weed Control System - Technical Bulletin." Dow AgroSciences.

Page 7-21
DAS.2013. "Supplemental Documentation in Support of Environmental Assessments in 

Response to Questions 8-11 Received December 12, 2012 regarding DAS-40278-9 corn 

and DAS-68416-4 soybean. Herbicide drift issues

". Ed. Hoffman, Neil.

Department of Primary Industries. "Using Buffer Zones and Vegetative Barriers." Web. August 

6, 2013 http://www.dpi.vic.gov.au/agriculture/farming-management/chemicaluse/agricultural-chemical-use/spraying-spray-drift-and-off-target-damage/ag0860-usingbuffer-zones-and-vegetative-barriers-to-reduce-spray-drift.

Dexter, A.G. 1993. Herbicide Spray 

Drift. http://library.ndsu.edu/tools/dspace/load/?file=/repository/bitstream/handle/10365/

3067/126dex93.pdf?sequence=1.

Driftwatch. "National Specialty Crop Site Registry." Web. August 6, 2013 

(https://driftwatch.org/.) 

Feitshans, T.A. 1999. "An analysis of state pesticide drift laws." San Joaquin Agriculture Law 

Review 9.37: 37-93. http://nationalaglawcenter.org/assets/bibarticles/feitshans_drift.pdf.

Fishel, Fred. 1997. "Pesticides and the Environment."

Heap, I. 2011. "The International Survey of Herbicide Resistant Weeds." (2011). Web. April 24, 

2011 www.weedscience.com.

Industry Task Force. 2006. "Environmental fate of 2,4-

D." http://www.24d.org/backgrounders/body.aspx?pageID=30&contentID=134.

Industry Task Force II. 2013. "FAQs." Copyright 2013 Industry Task Force II on 2,4-D 

Research Data 2013. 

Web http://www.24d.org/faqs/default.aspx?pageID=10&contentID=174&#q0.

Jordan, T., N. Glenn, B. Johnson, and T. Bauman. 2009. "Reducing Spray Drift from Glyphosate 

and Growth Regulator Herbicide Drift Caution." Purdue University Weed Science 2009. 

Web. March 14 

2011 http://www.ag.purdue.edu/btny/weedscience/Documents/ReducingDrift09.pdf.

Madden, Nicholaus M. , Randal J. Southard, and Jeff P. Mitchell. 2009. Soil Water Content and 

Soil Disaggregation by Disking Affects PM10 Emissions: University of California-Davis.

Maynard, E, B Overstreet, and J. Riddle. 2012. "Pesticide Drift and Organic Production." 

Driftwatch. Purdue Extension 2012. Web. August 6, 

2013 http://www.extension.purdue.edu/extmedia/HO/DW-1-W.pdf.

Mohr, M. "Reducing Pesticide Drift. Specialty Crops and Conventional Crops as Good 

Neighbors." Web. August 6, 2013 https://mys.extension.uiuc.edu/documents/960111006110611/reducingdrift.pdf.

National Pesticide Information Center. 2,4-D Technical Fact 

Sheet. http://npic.orst.edu/factsheets/2,4-DTech.pdf.

Nice, G.R.W., B. Johnson, and T.T. Bauman. 2004. Amine or ester, which is 

better? http://www.btny.purdue.edu/weedscience/2004/articles/amineester04.pdf.

Owen, M. D., B. G. Young, D. R. Shaw, R. G. Wilson, D. L. Jordan, P. M. Dixon, and S. C. 

Weller. 2011. "Benchmark study on glyphosate-resistant crop systems in the United 

States. Part 2: Perspectives." Pest Management Science 67.7: 747-

57. http://www.ncbi.nlm.nih.gov/pubmed/21452168.

Owen, M.D.K. 2008. "Weed species shifts in glyphosate-resistant crops." Pest Management 

Science 64.4: 377-87. http://www.ncbi.nlm.nih.gov/pubmed/18232055.

Page 7-22
Schultz, H.B., N.B. Akesson, W.E. Yates, and K.H. Ingebretson. 1956. "Drift of 2,4-D applied 

by plane." California Agriculture.August: 4-

14. http://ucce.ucdavis.edu/files/repositoryfiles/ca1008p4-64547.pdf.

Towery, D., and S. Werblow. 2010."Facilitating Conservation Farming Practices and Enhancing 

Environmental Sustainability with Agricultural Biotechnology." 28. Web. November 9, 

2010 http://www.ctic.purdue.edu/media/pdf/Biotech_Executive_Summary.pdf.

Tu, M., C. Hurd, and JM Randall. 2001Weed Control Methods Handbook: Tools and Techniques 

for Use in Natural Areas. Ed. Conservancy, The Nature: UC Davis, CA.

University of Missouri. 1997. "Pesticides and the Environment." 1997. 

Web http://extension.missouri.edu/p/G7520.

US-EPA.2013. "2,4-D Final Work Plan - Registration Review Case Number 73." Ed. Office of 

Chemical Safety and Pollution Prevention. Washington, D.C.: U.S. Environmental 

Protection Agency. Vol. 2013 of Docket Number EPA-HQ-OPP-2012-

0330. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0330-0024.

US-EPA. 2005a. "2,4-D RED Facts." 2005a. Web. August 10 

2011 http://www.epa.gov/oppsrrd1/REDs/factsheets/24d_fs.htm.

US-EPA.2012a. "2,4-D. Human Health Assessment Scoping Document in Support of 

Registration Review." Ed. Office of Chemical Safety and Pollution Prevention. 

Washington, D.C.: U.S. Environmental Protection Agency. 36. Vol. 

2013. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0330-0004.

US-EPA. 2005b. "Attachment III: Environmental Risk Assessment of Plant Incorporated 

Protectant (PIP) Inert Ingredients." U.S. Environmental Protection Agency 2005b. Web. 

July 20 

2011 http://www.epa.gov/scipoly/sap/meetings/2005/december/pipinertenvironmentalrisk

assessment11-18-05.pdf.

US-EPA.2012b. "EPA Denial of November 6, 2008 NRDC Petition to Cancel All 2,4-D 

Registrations." Ed. Wu, Dr. Solomon and Ms. Personnal Communication ed.

US-EPA. 2004. "Glyphosate Analysis of Risks to Endangered and Threatened Salmon and 

Steelhead." U.S. Environbmental Protection Agency 2004. Web. January 24 

2012 http://www.epa.gov/espp/litstatus/effects/glyphosate-analysis.pdf.

US-EPA. 2012c. "Pesticide issues in the works: pesticide volatilization." 2012c. 

Web http://www.epa.gov/opp00001/about/intheworks/volatilization.htm.

US-EPA. 2010. "Pesticide Registration Manual: Chapter 11 - Tolerance Petitions." U.S. 

Environmental Protection Agency 2010. Web. November 3 

2011 http://www.epa.gov/pesticides/bluebook/chapter11.html.

US-EPA. 2000. Profile of the Agricultural Crop Production Industry. Washington: U.S. 

Environmental Protection Agency-Office of Compliance Sector Notebook 

Profile. http://www.epa.gov/compliance/resources/publications/assistance/sectors/notebo

oks/agcrop.pdf.

US-EPA.2008. "Quizalofop Final Work Plan - Registration Review of Quizalofop-ethyl 

(128711) and Quizalofop-p-ethyl (128709)." Ed. Office of Prevention, Pesticides, and 

Toxic Substances,. Washington, D.C.: U.S. Environmental Protection Agency. 8 of 

Docket Number EPA-HQ-OPP-2007-

1089. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2007-1089-0026.

US-EPA. 2007. Quizalofop Summary Document, Registration Review: Initial Docket, December 

2007, Case Number 7215.

Page 7-23
US-EPA. 1993. R.E.D. Facts – Glyphosate. Prevention, Pesticides and Toxic Substances 

Washington: U.S. Environmental Protection 

Agency. http://www.epa.gov/oppsrrd1/REDs/factsheets/0178fact.pdf.

US-EPA. 2009. Registration Review- Preliminary Problem Formulation for the Ecological Risk 

and Drinking Water Exposure Assessments for Glyphosate and Its Salts (PC Code 

417300, 103601, 103604, 103607, 103608, 103613, 103603, 103605, 128501).

Washington, D.C. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP2009-0361-0007.

US-EPA. 2005c. Reregistration Eligibility Decision for 2,4-D. Washington: U.S. Environmental

Protection Agency. http://www.epa.gov/oppsrrd1/REDs/24d_red.pdf.

US-EPA. 2002. "Summary of Analytical Chemistry and Resdue Data for Registration of 

Trangenic Cotton (ID# 0F06140)."

USDA-NASS. 2006. Agricultural Chemical Usage 2005 Field Crops Summary: United States 

Department of Agriculture - National Agricultural Statistics 

Service. http://usda.mannlib.cornell.edu/usda/nass/AgriChemUsFC//2000s/2006/AgriChe

mUsFC-05-17-2006.pdf.

USDA-NRCS. 2000. Conservation Buffers to Reduce Pesticide Losses. USDA: 

USDA. http://www.in.nrcs.usda.gov/technical/agronomy/newconbuf.pdf.

Page 7-24
Appendix 8. Herbicides used on DAS Corn and Soybean

Page 8-1
Herbicides Used on DAS Corn and Soybean

Three petitions submitted by DAS to APHIS seek determinations of nonregulated status for GE 

maize and soybean cultivars engineered for resistance to herbicides. The three petitions are as 

follows:

APHIS Petition 09-233-01p (DAS, 2010a) is for GE maize (Zea mays) designated as event DAS40278-9 corn. It is engineered for increased resistance to certain broadleaf herbicides in the 

phenoxy auxin group such as 2,4-D (2,4-dichlorophenoxyacetic acid). DAS-40278-9 corn is also 

resistant to grass herbicides classified as aryloxyphenoxypropionate (AOPP) acetyl coenzyme A 

carboxylase (ACCase) inhibitors, such as quizalofop-p-ethyl (quizalofop), that are referred to as 

fop herbicides.

APHIS Petition 09-349-01p (DAS, 2010b) is for a GE soybean (Glycine max) variety designated 

DAS-68416-4 soybean. The aad-12 gene in DAS-68416-4 soybean expresses the AAD-12 

protein, which degrades 2,4-D into herbicidally inactive 2,4-dichlorophenol. DAS-68416-4 

soybean also contains the PAT protein, conferring resistance to the herbicide glufosinate.

APHIS Petition Number 11-234-01p (DAS, 2011d) is for non-regulatory status determination of 

event DAS-44406-6 soybean, which is genetically engineered for increased resistance to certain 

broadleaf herbicides, including the nonselective herbicides glufosinate, glyphosate, and 2,4-D.

The only difference between these two soybean events is that resistance to glyphosate in DAS68416-4 soybean will be achieved by traditional breeding with another soybean containing the 

2mEPSPS gene, while DAS-44406-6 soybean has been genetically engineered with this gene.

A brief overview of the four herbicides (glyphosate, 2,4-D, quizalofop, and glufosinate) that are 

intended to be used on the three DAS events are presented in the following sections. The 

proposed uses of these herbicides on DAS-40278-9 corn and DAS-68416-4 soybean (which 

would also include DAS-44406-6 soybean) and any EPA assessments performed assessing the 

potential effects from the new uses are summarized.

2,4-D 

Background and Current Uses

2,4-D is in the phenoxy or phenoxyacetic acid family and is listed as an herbicide, a plant growth 

regulator, and has been reported to elicit fungicidal properties at concentrations in ex cess of 

approved application rates. Its main use is as a selective post-emergence herbicide for 

controlling broadleaf weed species. The herbicide is approved for use on a wide variety of crops 

and has more than 600 registered end-use products for use on more than 300 distinct agricultural 

and residential sites, including terrestrial and aquatic settings (US-EPA, 2005b). Agriculturally, 

it is used on a variety of crops including corn, rice, sorghum, sugar cane, wheat, rangeland, and 

pasture. In addition, 2,4-D is used to control unwanted vegetative growth on utility corridors, 

rights-of-way, roadsides, non-crop areas, managed forest, and lawn and turf areas. It is also used 

to control aquatic and nuisance weeds, e.g., purple loosestrife (Industry Task Force II, 2005). 

2,4-D controls many broadleaf weeds including carpetweed, dandelion, cocklebur, horseweed, 

morning glory, pigweed sp., lambsquarters, ragweed spp., shepherd’s-purse, and velvetleaf. It 

Page 8-2
causes some plant damage to grasses at early growth stages in corn, and little to no plant damage 

in other grasses such as wheat and rice (Industry Task Force II, 2005).

The herbicide 2,4-D is currently available in ten molecular forms: 2,4-dichlorophenoxyacetic 

acid, dimethylamine salt of 2,4-D, 2-ethylhexyl ester of 2,4-D, butoxyethyl ester of 2,4-D, 

triisopropanolamine salt of 2,4-D, isopropylamine salt of 2,4-D, diethanolamine salt of 2,4-D, 

sodium salt of 2,4-D, isopropyl ester of 2,4-D, and choline salt of 2,4-D (US-EPA, 2013b). 2,4-

D is formulated primarily as an amine salt in an aqueous solution or as an ester in an emulsifiable 

concentrate (US-EPA, 2005b). 

The mode of action of 2,4-D is described as an “auxin mimic,” meaning that it kills the target 

weed by mimicking auxin plant growth hormones, such as indole acetic acid (IAA) (Tu et al., 

2001). Auxins and synthetic auxinic herbicides regulate virtually every aspect of plant growth 

and development; at low doses, auxinic herbicides possess similar hormonal properties to natural 

auxin (Kelley and Riechers, 2007). However, as rates increase, they can cause various plant 

growth abnormalities in sensitive dicots (Tu et al., 2001). Observable plant responses to 2,4-D 

can include epinasty, root growth inhibition, meristematic proliferation/callusing, leaf 

cupping/narrowing, stem cracking, adventitious root formation, senescence, and chlorosis. This 

uncontrolled and disorganized plant growth eventually leads to plant death when applied at 

effective doses (Tu et al., 2001). 2,4-D controls many broadleaf weeds including carpetweed, 

dandelion, cocklebur, horseweed, morning glory, pigweed sp., lambsquarters, ragweed spp., 

shepherd’s-purse, and velvetleaf (Industry Task Force II, 2005).

The 2,4-D mode of action as a synthetic auxin is not changed by the formulations, but the 

chemical and physical properties of each formulation influence the selection of equipment, 

mitigation measures adopted in the field to minimize off-target impacts, and formulation-specific 

safety measures. For a majority of uses, 2,4-D is combined with other herbicides because it 

economically enhances the weed control spectrum of many other herbicides, such as glyphosate, 

dicamba, mecoprop, and ALS herbicides (US-EPA, 2005b).

The degradation products of 2,4-D are 1,2,4-benzenetriol, 2,4-DCP, 2,4-dichloroanisole (2,4-

DCA), 4-chlorophenol, chlorohydroquinone (CHQ), volatile organics, bound residues, and 

carbon dioxide. The EPA has determined that residues other than 2,4-D and 2,4-DCP are not of 

risk concern due to low occurrence under environmental conditions, comparatively low toxicity, 

or a combination thereof (US-EPA, 2013b).

Using pesticide usage data from the USDA-NASS and Private Pesticide Market Research, EPA 

estimated that an average of nearly 29 million pounds of all forms of 2,4-D were applied to 

agricultural crops in the U.S. annually between 2006 and 2010 (US-EPA, 2012a). Based on 

average treated fraction of acreage, the crops with the highest uses of 2,4-D were: almond (15%), 

apples (20%), barley (25%), cherries (15%), fallow (25%), hazelnuts (25%), nectarines (15%), 

oats (15%), oranges (20%), peaches (20%), pears (15%), plums (15%), prunes (15%), sorghum 

(20%), sugarcane (40%), tangelos (30%), wheat (30%). All other treated crops averaged 10% or 

less of the total acreage grown (US-EPA, 2012a). Average annual use on lawns, turf, nurseries, 

etc. in commercial settings decreased from 5 million to 4 million pounds per year (2002, 2004,

2006). Homeowner and aquatic weed control uses have remained fairly constant with average 

annual uses of 9 to 9.5 million pounds per year (2003, 2005) (US-EPA, 2013b) .

Page 8-3
For 2,4-D, the current maximum approved usage rate is 4.0 lbs ae/A per year for asparagus, 

pome fruits, sugarcane, stone fruites, forestry uses, and non-cropland uses, among others. The 

maximum rate for aquatic uses is 10.8 lbs ae/acre foot for submerged aquatic plants. Typically, 

one to three applications are made per growing season. 2,4-D is currently registered in the U.S. 

for use on corn. The currently approved application rates for field corn and popcorn are a 

maximum per-year application rate of 3 lbs/acre and a maximum single application rate of 1.5 

lbs/acre (US-EPA, 2013b).

2,4-D is approved for use on soybean only for pre-plant burndown application. Application rates 

on soybean are 0.5 or 1.0 lbs ae/A per application or 1.0 lbs ae/A per crop per year. The 

herbicide may not be applied any later than 7 to 15 days (0.5–1.0 lb ae/A of ester formulations) 

or 15 to 30 days (0.5–1.0 lb ae/A of amine formulations) prior to planting due to the potential for 

crop injury (DAS, 2011a). 

Under Section 408 of FFDCA, EPA regulates the levels of pesticide residues that can 

remain on food or food commodities from pesticide applications (US-EPA, 2010b). The 

tolerance level is the maximum residue level of a pesticide that can legally be present in 

food or feed, and if pesticide residues are found to exceed the tolerance value, the food is 

considered adulterated and may be seized. The EPA establishes tolerances to regulate the 

amount of pesticide residues that can remain on food or feed commodities as the result of 

pesticide applications. Table 8-1 shows the current tolerances for residues of 2,4-D established 

for corn and soybean commodities (US-EPA, 2011a).

Table 8-1. 2,4-D Tolerances for Corn and Soybean Commodities

Commodity Residue (parts per million)

Corn, field, forage 6.0

Corn, field, grain 0.05

Corn, field, stover 50

Soybean, forage 0.02

Soybean, hay 2.0

Soybean, seed 0.02

Source: (US-EPA, 2011b)

EPA is currently conducting a registration review of 2,4-D which was begun in 2012 and is 

currently scheduled to be completed in 2017 (US-EPA, 2013a). According to EPA, as part of 

their review, a comprehensive ecological risk assessment, including an endangered species 

assessment, will be prepared for all uses of 2,4-D. Additionally, EPA will conduct revised 

dietary, residential, and occupational risk assessments, incorporating any new toxicological or 

other relevant data (US-EPA, 2013a). All documents related to the 2,4-D registration review can 

be viewed at the registration review docket:

http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2012-0330

Page 8-4
New 2,4-D Choline Salt Formulation and Uses

DAS has developed a new herbicide formulation containing 2,4-D choline salt (DAS, 2010b; 

DAS, 2010a; DAS, 2011a) for additional pre- and post-emergence use with DAS-40278-9 corn, 

DAS-68416-4 soybean, and DAS-44406-6 soybean. The 2,4-D-resistance traits allow for a later 

application of the herbicide in both soybean (R2 stage) and corn (V8 stage). The new 

formulation is reported to be chemically more stable, making it less volatile, than the currently 

used amine or ester formulations of 2,4-D. In addition, the new formulation is reported to have 

minimized potential for physical drift in comparison to the currently used 2,4-D ester and 2,4-D 

dimethylamine (DMA) formulations, as well as decreased odor and improved handling (DAS, 

2011a; DAS, 2011e). 

2,4-D choline salt is a quaternary ammonium salt that rapidly dissociates into a 2,4-D anion and 

a choline cation. 2,4-D choline salt is currently registered on a number of crops including: 

sugarcane, rice, pome fruits, stone fruits, conventional corn and soybeans, fallow land, turf, and 

tree and brush control. Dow Agrosciences LLC, the manufacturer and registrant of 2,4-D 

choline salt, has submitted applications to EPA to add the following uses to the current 2,4-D 

choline salt labels: 1) DAS-40278-9 corn, 2) DAS-68416-4 soybean, 3) EnlistTM corn (DAS40278-9 corn stacked with a glyphosate-resistance trait), and EnlistTM soybean (DAS-68416-4 

soybean stacked with a glyphosate-resistance trait).

Two of the proposed registrations contain only 2,4-D choline salt as the active ingredient, 

whereas the other two labels are for a 2,4-D-choline salt/glyphosate mixture which DAS plans to 

market under the name Enlist DuoTM. The latter would allow applications to GE herbicideresistant corn and soybean with resistance to both 2,4-D and glyphosate. The 2,4-D choline 

formulation GF-2654 TS would be used on DAS 68416-4 soybean and the 2,4-D choline 

formulation GF-2654 TC used on DAS-40278-9 corn. The Enlist DuoTM formulations GF-2726 

and GF-2727, containing both 2,4-D choline salt and glyphosate, would be applied on EnlistTM 

corn and EnlistTM soybean, respectively.

Proposed New 2,4-D Use on Corn

Although 2,4-D is already used on corn, its use is limited beyond early seedling stages (Wright et 

al., 2010). Applications of 2,4-D as a post-emergent herbicide at later growth stages in 

conventional corn can cause significant malformations (Wright et al., 2010). The proposed new 

use of 2,4-D choline on DAS-40278-9 corn includes a pre-emergent and up to two post-emergent 

applications (DAS, 2011b). Table 8-2 compares the current the use patterns for 2,4-D on field 

corn with the proposed use patterns for 2,4-D on DAS-40278-9 corn. The comparison is also 

shown graphically in Figure 8-1.

The label directions indicate no more than one pre-emergence application and no more than two 

post-emergence applications per use season. Proposed application rates for this new use of 2,4-D 

on DAS-40278-9 corn are up to 1 lb acid equivalent (ae)/acre (1,120 g ae/ha) as a pre-emergent 

herbicide and up to two applications between 0.5 to 1.0 lbs ae/acre (560 and 1,120 g ae/ha) for 

post-emergence. The post-emergence applications must be at a minimum of 12-days apart 

during the first 3-5 weeks before the corn reaches 6-8 inches in height and again up to the V8 

[48-inch] stage of corn. These application rates are based on the currently approved rates for 

field corn and popcorn, which establish a maximum-per-year application rate of 3 lbs/acre, and a 

Page 8-5
maximum single application rate of 1.5 lbs/acre (DAS, 2011f). Post-emergence application of 

2,4-D, as specified on the draft label, could not occur within 30 days of forage harvest. The 

proposed preharvest interval (PHI) for corn is 30 days. Applications are to be made using 

groundboom equipment. Aerial application and chemigation are prohibited. The new use 

pattern and draft label are subject to regulatory approval by EPA. 

Table 8-2: Comparison of Current and Proposed Application Rates for 2,4-D on Corn

Crop Stage

Conventional Field Corn Proposed New Use on DAS-40278-9 Corn

Maximum 

Application Rate 

(lb/acre)1,2

Directions and Timing

Maximum 

Application 

Rate (lb/acre)1,2

Directions and Timing

Pre-plant or 

Pre-emergence

1.0

Apply before corn 

emerges to control 

emerged broadleaf 

weed seedlings or 

existing cover crops

1.0

Apply before corn emerges 

to control emerged 

broadleaf weed seedlings 

or existing cover crops

Post-emergence 0.5

Apply when weeds are 

small and corn is less 

than 8 inches tall (to top 

of canopy). When corn 

is over 8 inches tall, use 

drop nozzles and keep 

spray off foliage.

0.5 to 1.0

Apply after crop and weed 

emergence but before corn 

exceeds growth stage V8 or 

48” in height, whichever 

occurs first.

Make 1 to 2 applications 

with a minimum of 12 days 

between applications.

Pre-harvest 1.5 Apply after hard dough 

(or at denting) stage. --- ---

Total Annual 

Maximum 

Application

3.0 --- 3.0 ---

Source: (DAS, 2011f)

1. All values expressed as acid equivalents. 

2. 1 lb/acre is the equivalent of 1,120 g/hectare.

Page 8-6
Source: (DAS, 2012b).

Figure 8-1. Current use pattern of 2,4-D on conventional corn and proposed new use of 

2,4-D choline salt on DAS-40278-9 corn.

New 2,4-D Use on Soybean

Currently, 2,4-D is approved for use on soybean only for pre-plant burndown application. 

Application rates on soybean are 0.5 or 1.0 lbs ae/A per application or 1.0 lbs ae/A per crop per

year (US-EPA, 2005b). It may not be applied any later than 7 to 15 days (0.5–1.0 lb ae/A of 

ester formulations) or 15 to 30 days (0.5–1.0 lb ae/A of amine formulations) prior to planting due 

to the potential for crop injury (DAS, 2010b).

The proposed new use of 2,4-D choline on DAS-68416-4 soybean (or DAS-44406-6 soybean) 

includes a single pre-plant or pre-emergent application and up to two post-emergent applications 

(DAS, 2011b). Specifically, an application of 2,4-D at pre-plant/burndown or pre-emergence 

(1.0 lb ae/A) without plant back restrictions would be allowed and/or one or two over-the-top 

post-emergence applications (0.5 - 1.0 lb ae/A) at least 12 days apart up to the R2 stage (full 

flower) of development (see Figure 8-2) (DAS, 2010b). Thus, the proposed maximum total 

seasonal application rate of 2,4-D on DAS-68416-4 soybean (or DAS-44406-6 soybean) would 

increase from 1.0 lb ae/A (current) to 3.0 lb ae/A per year. (This proposed new seasonal rate is 

the same current EPA-approved maximum annual use rate of 2,4-D for popcorn and field corn). 

Post-emergence application of 2,4-D, as specified on the draft label, could not occur within a 

PHI of 30 days (DAS, 2011a; DAS, 2011c). The new use pattern and draft label are subject to 

regulatory approval by EPA. Table 8-3 presents a comparison of the current and proposed 

Page 8-7
application rates of 2,4-D on soybean and DAS-68416-4 (or DAS-44406-6 soybean) (DAS, 

2010b).

Source: (DAS, 2010b).

Note: the new 2,4-D use pattern would be the same for DAS-44406-6 soybean.

Figure 8-2. Proposed 2,4-D Application Rates on DAS-68416-4 Soybean Compared to 

Current Application Rates Permitted for Conventional Soybean

Table 8-3. Comparison of Current and Proposed Application Rates of 2,4-D on Soybean 

Crop Stage

Current Use Pattern -

Conventional Soybean

Proposed New Use Pattern –

DAS-68416-4 Soybean (or DAS-44406-6 

Soybean)

Maximum 

Application 

Rate (lb/acre)1

Directions 

and Timing

Maximum 

Application 

Rate (lb/acre)1 Directions and Timing

Pre-plant 

(burndown) or 

Pre-emergence

0.5 -1.0

Pre-plant:

Apply before 

soybean 

emerges to 

control 

emerged 

broadleaf 

weed seedlings 

or existing 

cover crops

1.0

Pre-plant: Apply any time 

prior to and up through 

soybean planting but before 

soybean emerges to control 

emerged broadleaf weed 

seedlings or existing cover 

crops.

Pre-emergence: Apply any

time after planting but before 

soybean emerges to control 

broadleaf weed seedlings or 

existing cover crops.

Page 8-8
Crop Stage

Current Use Pattern -

Conventional Soybean

Proposed New Use Pattern –

DAS-68416-4 Soybean (or DAS-44406-6 

Soybean)

Maximum 

Application 

Rate (lb/acre)1

Directions 

and Timing

Maximum 

Application 

Rate (lb/acre)1 Directions and Timing

Postemergence --2 -- 0.5-1.0

Apply when weeds are small 

and soybean growth stage is 

no later than R2 (full 

flowering stage).

Make one to two applications 

with a minimum of 12 days 

between applications.

Total Annual 

Maximum 

Application

1.0 -- 3.0 --

1 All values expressed as acid equivalents 

2 Not applicable

Source: (DAS, 2011c).

EPA Assessments of Proposed New 2,4-D Choline Salt Formulation and Uses on 2,4-DResistant Corn and Soybean

Under FIFRA, EPA regulates the use of herbicides, requiring registration of a pesticide for a 

specific use prior to distribution or sale of the pesticide for a proposed use pattern. The process 

of registering a pesticide is a scientific, legal, and administrative procedure through which EPA 

examines the ingredients of the pesticide; the particular site or crop on which it is to be used; the 

amount, frequency, and timing of its use; and storage and disposal practices. In evaluating a 

pesticide registration application, EPA assesses a wide variety of potential human health and 

environmental effects associated with use of the product. Prior to registration for a new use for a 

new or previously registered pesticide, the producer of the pesticide must provide data from tests 

done according to EPA guidelines. EPA must determine through this submitted test data that the 

pesticide will not cause unreasonable adverse effects on the environment and non-target species 

when used in accordance with label instructions and will result in a reasonable certainty of no 

harm to humans. 

EPA must also approve the language used on the pesticide label in accordance with 40 CFR part

158. The EPA pesticide registration process involves the design of use restrictions that, if 

followed, have been determined to be protective of worker health. Growers are required to use 

pesticides consistent with the application instructions provided on the EPA-approved pesticide 

labels. The overall intent of the label is to provide clear directions for effective product 

performance while minimizing risks to human health and the environment (US-EPA, 2010c). 

Page 8-9
Based on the studies submitted on 2,4-D choline salt formulation by DAS, EPA has conducted 

draft assessments on the potential environmental fate, ecological effects, and human health 

effects of the proposed new uses of 2,4-D choline salt. The conclusions from those assessments 

are summarized in this section. EPA will be publishing these complete draft analyses in the 

Federal Register for public comment.

Environmental Fate and Ecological Risks

EPA Environmental Fate and Effects Division (EFED) assessed the ecological risks to listed and 

non-listed species associated with the proposed new uses of 2,4-D choline salt on 2,4-D-resistant 

corn and soybean. The assessment examined the effects of 2,4-D choline salt (and 2,4-DCP, 

when relevant) on aquatic and terrestrial environments primarily through the routes of spray 

drift, volatile (vapor) drift, and runoff. Modeled application rates represent the maximum use

patterns of the proposed labels for use on 2,4-D-resistant corn and soybean.

The results are summarized as follows:

No potential direct risks from the proposed applications of 2,4-D choline salt to herbicidetolerant corn and soybeans were identified for the following:

• Birds (chronic),

• Aquatic plants,

• Freshwater fish (acute and chronic),

• Estuarine/marine fish (acute and chronic),

• Freshwater invertebrates (acute and chronic),

• Estuarine/marine invertebrates (acute and chronic),

• Aquatic plants, and 

• Terrestrial insects.

The screening level risk assessment for non-listed species identified these groups as being 

potentially at direct risks from exposures from the proposed new uses of 2,4-D choline salt:

• Mammals (acute and chronic),

• Birds, reptiles, terrestrial-phase amphibians (acute), and

• Terrestrial plants.

In addition, the screening level risk assessment identified all non-listed taxa as potentially at 

indirect risks from the proposed uses of 2,4-D choline salt because of potential dependencies

(e.g., food, shelter, habitat) on species that are directly affected. Information, such as biological 

distribution, species biology, spray drift properties specific to the 2,4-D choline formulations, 

and mitigation efforts in regions where the pesticide is used, could be used to reduce the 

uncertainty regarding potential direct and indirect effects.

An assessment of the direct and indirect risks to listed species for which a potential for risk was 

identified in the screening level assessment is under development by EPA. This assessment will 

address the specific geographical and biological characteristics of each species potentially at 

risks from exposures to 2,4-D. When this refined, species-specific assessment is completed, 

Page 8-10
EPA will be able to identify which species are at direct and indirect risks from exposures to 2,4-

D.

A spray drift analysis using the GF2726 formulation indicated that buffers could reduce risk 

quotients for birds (acute), mammals (acute and chronic), and terrestrial plants below the 

Agency’s levels of concern. The results of the buffer analysis indicated that riskes below levels 

of concern can only be achieved through the combination of the AIXR 11004 nozzle and GF2726 formulation. Final species-specific buffer distances remain uncer review and refinement. 

The locations of the buffers would be dependent on species distribution, species biology, and any 

mitigation efforts proposed by the registrant.

EPA will be publishing these complete draft analyses in the Federal Register for public 

comment.

Human Health Risk Assessment

The EPA Health Effects Division (HED) of the Office of Pesticide Programs (OPP) is charged 

with estimating the risk to human health from exposure to pesticides. HED evaluated hazard and 

exposure data and conducted dietary, residential (non-occupational), aggregate, and occupational 

exposure assessments to estimate the risk to human health that will result from the proposed new 

use of 2,4-D choline salt on 2,4-D-resistant corn and soybean. Based on their draft human health 

risk assessment, EPA HED recommends for a registration for the use of 2,4-D choline on 2,4-Dresistant corn and soybean. EPA identified additional data needed, specific tolerance 

recommendations, and label modifications. A summary of the results of the assessment are 

provided, below. The draft assessment will be published by EPA in the Federal Register for 

public review and comment.

Hazard Characterization: Based on its review of hazard data, EPA concluded that 2,4-D’s

principal toxic effects are changes in the kidney, thyroid, liver, adrenal, eye, and ovaries/testes in 

the rat following exposure via the oral route at dose levels above the threshold of saturation of 

renal clearance. No systemic toxicity was observed in rabbits following repeated exposure via

the dermal route at dose levels up to the limit dose. Neurotoxicity was observed in the acute

neurotoxicity study in rats at the high dose. In an extended 1-generation reproductive toxicity 

study in rats, reproductive toxicity, developmental neurotoxicity, and immunotoxicity were not 

observed, and the thyroid effects observed at dose levels up to/approaching renal saturation were 

considered treatment-related, although not adverse. Maternal and developmental toxicity were 

observed at high dose levels exceeding the threshold of saturation of renal clearance. There are 

no residual uncertainties for pre- and/or postnatal toxicity. 2,4-D is not acutely (lethal) toxic via 

the oral, dermal, and inhalation routes, is not a dermal irritant or a dermal sensitizer, but it is a 

severe eye irritant. 2,4-D has been classified as a Category D chemical, i.e., not classifiable as to 

human carcinogenicity.

Dietary Exposure and Risk Assessment: Acute and chronic aggregate (food + dietary drinking

water) exposure and risk assessments were conducted for the new proposed use of 2,4-D choline 

salt. EPA HED determined that the resulting acute food plus drinking water risk estimates are 

not of concern to (≤100% of the acute population adjusted dose (aPAD)) at the 95th percentile of 

the exposure distribution for the general population and all population subgroups. The resulting 

acute risk estimate for children 1 to 2 years old (the subgroup with the greatest exposure) was 

Page 8-11
14% of the aPAD at the 95th percentile of the exposure. The resulting chronic risk estimates are 

not of concern to EPA HED for the general population and all population subgroups. The most 

highly exposed population was children 1 to 2 years old, utilizing 15% of the chronic PAD 

(cPAD). 

Residential (Non-Occupational) Exposure and Risk Assessment: There is no potential hazard 

via the dermal route for 2,4-D, therefore the handler assessment included only the inhalation 

route of exposure and the post-application assessment included only the inhalation and incidental 

oral route of exposure. The residential handler and post-application risk estimates are not of 

concern for 2,4-D for all scenarios and all routes of exposure. 

Exposure to drift and volatilization, and the appropriate available data, were considered in this 

assessment due to the anticipated market expansion. Concerning spray drift, the residential postapplication exposure assessment for registered use as direct application to turf is protective of 

potential deposition on turf from spray drift for the proposed use of 2,4-D choline on herbicidetolerant corn and soybean. The potential exposure to vapor phase 2,4-D residues emitted from 

treated fields for the proposed uses of 2,4-D choline has been evaluated in this assessment. The 

results indicate that volatilization of 2,4-D from treated crops does occur and could result in 

bystander exposure to vapor phase 2,4-D. Modeling results, however, indicate that airborne 

concentrations, even at the edge of the treated fields, are not of concern. 

Aggregate Risk Estimates: The acute aggregate risk assessment include only food and water 

exposure. The resulting acute food plus drinking water risk estimates are not of concern to EPA 

HED (≤100% aPAD) at the 95th percentile of the exposure distribution for the general population 

and all population subgroups.

The short-term aggregate risk assessment includes food, water, and residential exposure. 

According to EPA HED, the resulting short-term aggregate risks are not of concern (margins of 

exposure (MOEs) > level of concern (LOC) of 100) for adults and children.

There are no intermediate-term residential exposure to 2,4-D; therefore the intermediate-term 

aggregate risk assessment include only food and drinking water exposure. Furthermore, the 

chronic aggregate risk assessment includes only food and water exposure. The chronic food plus 

drinking water risk estimates are not of concern to EPA HED for the general population and all 

populations subgroups.

Occupational Exposure and Risk Assessment: Occupational handlers may apply 2,4-D choline 

with groundboom equipment. There is no potential hazard via the dermal route for 2,4-D, 

therefore the occupational handler assessment included only the inhalation route of exposure. 

Occupational handler inhalation risk estimates are not of concern (i.e., MOEs > LOC of 300) for 

all scenarios for use of 2,4-D choline on herbicide-tolerant corn and soybean. At baseline 

personal protective equipment (PPE) (i.e., no respirator), the occupational handler inhalation 

MOE is 4,900 for mixer/loaders and 3,200 for applicators using groundboom equipment. 

There is no potential hazard via the dermal route for 2,4-D; therefore, a quantitative occupational 

post-application dermal risk assessment was not completed. Furthermore, a quantitative postapplication inhalation risk assessment was not performed for workers at this time; although the 

assessment was not performed, other exposure scenarios are expected to be protective of 

Page 8-12
potential worker post-application inhalation exposure. The minimum Worker Protection 

Standard (WPS) restricted entry interval (REI) of 48 hours is adequate to protect agricultural 

workers from post-application exposures to 2,4-D. 

Glyphosate

Background and Current Uses

Glyphosate acid is a broad spectrum, nonselective systemic herbicide widely used to control most 

annual and perennial grass and broadleaf weeds in agricultural crops and non-agricultural sites. The 

herbicide is registered for pre- and post-emergence application on a variety of fruit, vegetable, and 

field crops, as well as for aquatic and terrestrial uses. Labeled uses of glyphosate include over 100 

terrestrial food crops as well as other non-food sites including forestry, greenhouse, non-crop, and 

residential. Glyphosate can also be used as a plant growth regulator and accelerate fruit ripening. 

Additionally, glyphosate is registered for use on GE glyphosate-resistant crops, including canola, 

corn, cotton, soybeans, alfalfa, and sugar beets. Glyphosate is the most widely used herbicide on 

U.S. corn and soybean. 

Glyphosate was first introduced under the trade name of RoundupTM by Monsanto in 1974. 

Glyphosate salts serve as the source of the active ingredient (ai) N-(phosphonomethyl) glycine 

and improve handling, performance, and concentration of the glyphosate acid. Glyphosate is 

distributed in several forms, including technical grade glyphosate, isoproplyamine salt, 

monoammonium salt, diammonium salt, N-methylmethanamine salt , trimethylsulfonium salt, or 

potassium salt (US-EPA, 2009c). Isopropylamine salt is the most typically used form in 

formulated products (Henderson, 2010).

Glyphosate acid is a nonselective Group 9 herbicide and kills plants by inhibiting the 5-

enolpyruvylshikimate-3-phosphate synthase (ESPS) enzyme. This enzyme is essential for the 

biosynthesis of aromatic amino acids (e.g., tyrosine, tryptophan, and phenylalanine) and other 

aromatic compounds in algae, higher plants, bacteria and fungi. By creating a deficiency in 

EPSP enzyme and aromatic amino acids production, glyphosate affects protein synthesis and 

plant growth (US-EPA, 2009c). Glyphosate is absorbed across the leaves and stems of plants 

and moves throughout the plant, concentrating in the meristem tissue (Henderson, 2010).

Based on pesticide usage data from USDA-NASS, private pesticide market research, and 

California Department of Pesticide Regulation (DPR), EPA estimated glyphosate usage from 

2004 through 2011. The crops with the highest glyphosate uses (based on average treated 

fraction of acreage) were: almond (85%), apples (55%), apricots (55%), asparagus (55%), 

avocados (45%), barley (20%), blueberries (20%), canola (65%), cherries (65%), corn (60%), 

cotton (85%), cucumbers (20%), dates (20%), dry beans/peas (25%), fallow (55%), figs (40%), 

grapefruit (80%), grapes (70%), hazelnuts (70%), kiwifruit (30%), lemons (70%), nectarines 

(45%), olives (45%), onions (30%), oranges (90%), peaches (55%), peanuts (20%), pears (65%), 

pecans (35%), peppers (20%), plums (65%), pumpkins (20%), rice (25%), sorghum (40%), 

soybeans (95%), squash (20%), sugar beets (50%), sugarcane (45%), sunflowers (55%), tangelos 

(55%), tangerines (65%), tomatoes (35%), walnuts (75%), and wheat (25%). All other treated 

crops averaged 15% or less of the total acreage grown (US-EPA, 2012e).

Page 8-13
The CP4 EPSPS protein confers resistance to glyphosate and has been used in many Roundup 

ReadyTM crops (e.g., canola, corn, cotton, soybean, and sugar beet). Glyphosate may be used 

premergent, preplant incorporated, or postemergent with Roundup ReadyTM crops. As listed on 

the RoundupTM herbicide labels, Roundup Original MAXTM, Roundup WeatherMAXTM, and 

Roundup PowerMAXTM products contain 48.8 percent of the potassium salt of glyphosate, 

equivalent to 4.5 lb of glyphosate ae per gallon (540 g glyphosate per liter (L)). Glyphosate is 

also commonly used in conjunction with many other herbicides as a tank mix for both preplant/pre-emergence weed control up through the 12-leaf stage or until the corn reaches a height 

of 30 inches (see, e.g., Loux et al., 2011). 

The current approved maximum pre-emergence application of glyphosate on glyphosate-resistant 

corn or soybeans is 3.7 lbs ae/acre. A glyphosate post-emergence application from 0.75 to 1.5 

lbs ae/acre (total 2.25 lbs/acre/season post-emergence) and an additional pre-harvest application 

of 0.77 lbs/ae/acre are permitted. The current maximum total seasonal use rate for glyphosate on 

glyphosate-resistant corn and soybean is 6 lbs ae/acre (DAS, 2012c).

Pesticide residue tolerances for glyphosate are listed in 40 CFR Part 180.364, representing

combined residues of glyphosate, N-(phosphonomethyl)glycine and its metabolite N-acetylglyphosate (expressed as glyphosate) (US-EPA, 2010a). Table 8-4 shows the current tolerances 

for residues of glyphosate established for corn and soybean commodities.

Table 8-4. Glyphosate Tolerances for Corn and Soybean Commodities

Commodity Residue (parts per million)

Corn, field, forage 13

Corn, field, grain 5

Corn, field, stover 100

Soybean, forage 100

Soybean, hay 200

Soybean, hulls 120

Soybean, seed 20

Source: (US-EPA, 2010a).

EPA is currently conducting a registration review of glyphosate which was begun in 2009 and is 

currently scheduled to be completed in 2015 (US-EPA, 2009b). According to EPA, as part of 

their review, “the Agency plans to require a number of ecological fate and effects studies, an acute 

and subchronic neurotoxicity study, and an immunotoxicity study through a data call-in, which is 

expected to be issued in 2010. The new information will be used to conduct a comprehensive 

ecological risk assessment, including an endangered species assessment, as well as a revised 

occupational human health risk assessment, for all glyphosate pesticidal uses (US-EPA, 2009b).”

All documents related to the glyphosate registration review can be viewed at the registration

review docket:

http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2009-0361

Page 8-14
Glyphosate Use on DAS-40278-9 Corn, DAS-68416-4 Soybean, and DAS-44406-6 

Soybean

DAS’ new pre-mix of 2,4-D choline and glyphosate DMA, the EnlistTM Duo formulations GF2726 and GF-2727, will be formulated as an approximate 1:1 ratio of 2,4-D choline to 

glyphosate DMA. If approved by EPA, glyphosate could be applied to EnlistTM Corn and 

EnlistTM Soybean (DAS-40278-9 corn and DAS-68416-4 soybean stacked with a glyphosateresistance trait (or DAS-44406-6 soybean) at pre-plant/burndown at 0.5 to 1.0 lb ae/acre and up 

to two post-emergence applications at 0.5 to 1.0 lb ae/, for a maximum total seasonal application 

rate of 3.0 lb ae/acre. This compares to current glyphosate use on glyphosate-resistant corn and 

soybeans of a maximum pre-emergence application of 3.7 lbs ae/acre and post-emergence 

applications from 0.75 to 1.5 lbs ae/acre (total 2.25 lbs/acre/season post-emergence) and an 

additional pre-harvest application of 0.77 lbs/ae/acre. The current maximum total seasonal use 

rate for glyphosate on glyphosate-resistant corn and soybeans is 6 lbs ae/acre (DAS, 2011f; DAS, 

2012a). 

Quizalofop

Background and Current Uses

Quizalofop-p-ethyl is a selective, systemic post-emergence phenoxy herbicide that is toxic to 

many annual and perennial grasses. It belongs to a subclass of phenoxy compounds known as 

aryloxyphenoxys (“fops”). Quizalofop-p-ethyl is absorbed from the leaf surface and is moved 

throughout the plant. It accumulates in the active growing regions of stems and roots. Most nongraminaceous plants (dicots and sedges) are tolerant to quizalofop. Dicotyledonous (or dicot) 

plants contain a prokaryotic form of ACCase (an enzyme found in chloroplasts) which is 

insensitive to “fop” herbicides. In contrast, monocotyledonous (or monocot) plants contain a 

sensitive eukaryotic form of ACCase in the plastid (DAS, 2010a). This is the primary reason 

that the “fop” herbicides are generally good graminicides1, with little activity on dicot plants. In 

addition, some grass species, including some cereal crops and weeds (e.g., annual bluegrass and 

wild oats), are tolerant of some of these herbicides (i.e., clethodim, quizalofop, and others) due to 

their ability to metabolize the herbicides to inactive forms (Devine and Shukla, 2000; Powles and 

Preston, 2009). 

The aryloxyphenoxypropionates (AOPP) herbicides inhibit chloroplastic ACCase, which 

catalyzes the first committed step in fatty acid biosynthesis, causing plant death (Burton et al., 

1989). The herbicidal activity of quizalofop-ethyl ester was first reported in 1983, and 

quizalofop-ethyl was first approved for use in a registered herbicide product in the U.S. in 1988 

(DAS, 2010a; DuPont, 2010).

2

 However, all end use product registrations were cancelled prior 

to 1996 and it was replaced by the more active quizalofop-P-ethyl (pure R-enatiomer of 

quizalofop racemic mixture), which first was approved for use in a registered product in 1990 

(DuPont, 2010).

1 A graminicide is an herbicide used for the control of grass weeds (of the former family ''Gramineae').'

2 Reference to the DuPont Assure® II label is for illustration only, and is not intended to infer any recommendation 

for the use of this product by APHIS or the USDA.

Page 8-15

 
The “fop” herbicides (AOPP ACCase inhibitors) have been registered for crop use for more than

20 years (USDA-APHIS, 2010). The “fop” herbicides traditionally have not been used to control 

weed species in cornfields because, as a grass (Poaceae family) species, corn is damaged by 

AOPP ACCase inhibitor activity. The registration and use of “fop” herbicides has been 

primarily on broadleaf crops, such as soybean, to control grass weed species, although certain 

cereal plant varieties have a level of tolerance to some “fops” (see DuPont, 2010). According to 

the USDA-NASS Agricultural Chemical Use Database, “fop” type herbicides were used for 

weed control on at least 23 food crop species between 1990 and 2006, totaling more than 16 

million pounds of active ingredient (USDA-NASS, 2011). 

The currently registered uses include canola, crambe, cotton, crops grown for seed, eucalyptus, 

dry beans (including Chickpea), dry and succulent peas, flaxseed, hybrid poplar plantings, 

lentils, mint (spearmint and peppermint), pineapple, ryegrass grown for seed, snap beans, 

soybeans, sugar beets, sunflowers, and noncrop areas. Current allowable rates for this herbicide 

vary from 0.0172 to 0.344 lb ai/acre, depending on crop and weed conditions (see EPA approved 

label for Assure II) (DAS, 2010a; DuPont, 2010). 

Pesticide residue tolerances for quizalofop are listed in 40 CFR Part 180.441. As quizalofop is 

not currently approved by EPA for use on corn, only residue limits for soybean commodities are 

shown in Table 8-5, representing combined residues of combined residues of quizalofop ethyl,

quizalofop, and quizalofop methyl (US-EPA, 2012b). 

Table 8-5. Quizalofop Tolerances for Soybean Commodities

Commodity Residue (parts per million)

Soybean, flour 0.5

Soybean, hulls 0.02

Soybean, meal 0.5

Soybean, seed 0.05

Soybean, soapstock 1.0

Source: (US-EPA, 2012b)

Note: quizalofop is not currently approved for uses on corn.

The Registration Review for quizalofop was begun in 2007 and a final workplan was completed 

in June of 2008. EPA has not published a proposed decision schedule for quizalofop as of this 

assessment:

http://www.epa.gov/oppsrrd1/registration_review/schedule.htm

Documents related to the EPA review are posted as part of the Registration Review of 

Quizalofop-ethyl (128711) and quizalofop-p-ethyl (128709) docket (EPA-HQ-OPP-2007-1089): 

http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2007-1089

New Use of Quizalofop on DAS-40278-9 Corn

DAS-40278-9 corn is a GE corn line that has increased resistance to treatment with phenoxy 

auxin herbicides (e.g., 2,4-D) and resistance to AOPP ACCase inhibitor (“fop”) herbicides 

(DAS, 2010a). DAS has indicated that “fop” herbicides could be used to maintain seed purity in 

DAS-40278-9 corn breeding nurseries, hybrid production fields, and generally for the control of 

Page 8-16
grass weeds in corn. As quizalofop is not currently registered for use as a post-emergent 

herbicide on corn, this is a proposed new use (DAS, 2010a). 

Quizalofop-P ethyl is the active ingredient in DuPont Assure IITM herbicide (EPA Reg. No. 352-

541). DuPont has submitted petitions to EPA to add the new use of quizalofop on DAS-40278-9 

corn. Since most grass crops, including corn, are highly sensitive to the herbicide, quizalofop 

could only be used on field corn that has been GE to be resistant to the herbicide, such as DAS40278-9 corn.

DuPont proposes a maximum single application rate of 0.082 lb ai/acre corn (DAS, 2011f). The 

proposed maximum application rate also is the seasonal maximum application rate (DAS, 

2011f). The proposed PHI is 30 days for forage; a PHI for corn grain or stover is not specified 

(US-EPA, 2011). This maximum application rate is less than that currently approved by EPA for 

use of quizalofop for the control of grassy weeds in soybeans and cotton, where a seasonal 

maximum application rate of 139 g ai/ha (0.124 lb ai/acre) is approved (DAS, 2011f). 

Applications of quizalofop would be made by broadcast foliar application by ground; aerial 

applications would be prohibited. EPA currently is reviewing the proposed label change for 

quizalofop and has not granted the registration yet. Table 8-6 provides a summary of the 

proposed application rates and directions for use on DAS-40278-9 corn. 

Table 8-6. Comparison of Current and Proposed Application Rates for Quizalofop

Crop Stage

Current Use Pattern for Quizalofop 

on Soybeans and Cotton Proposed New Use on DAS-40278-9 Corn

Maximum 

Application 

Rate (lb/acre)1,2

Directions and 

Timing

Maximum 

Application Rate 

(lb/acre)1,2

Directions and Timing

Postemergence

0.082

Apply 0.034 to 

0.082 lb/acre per 

application.

Do not exceed a 

total of 0.124 

lb/acre per season.

0.034 to 0.082

Apply 0.034 to 0.082 lb/acre per 

application from V2 – V6 

Growth stages.

Do not make more than 2

applications.

Do not exceed a total of 0.082 

lb/acre per season.

Do not apply later than V6 

growth stage.

Total Annual 

Maximum 

Application

0.124 --- 0.082 ---

Source: (DAS, 2011f).

Notes:

1. Active ingredient. 

2. 1 lb/acre is the equivalent of 1,120 g/hectare.

Page 8-17
Source: (DAS, 2010b).

Figure 8-3. Proposed Quizalofop Application Rate on DAS-40278-9 Corn.

EPA Assessments of Proposed New Use of Quizalofop on DAS-40278-9 Corn

Environmental Fate and Ecological Risks

As part of the approval process, EPA EFED performed a screening level ecological risk 

assessment for listed and non-listed species for the proposed label for quizalofop. The 

screening-level analysis for quizalofop-p-ethyl concluded that the proposed new agricultural use 

for quizalofop shows the possibility for direct effects to mammals (chronic dose-based risk), and 

terrestrial monocots. Direct risks were also assumed for aquatic vascular plants, and 

estuarine/marine fish (acute) because of an absence of data. Chronic risks were assumed for 

terrestrial birds because of nondefinitive toxicity endpoints. Since birds serve as surrogates for 

terrestrial-phase amphibians and reptiles, these taxa may also be at direct risk from the new uses 

of quizalofop-p-ethyl. Indirect effects were determined by assessing the potential for reduction 

of prey base or habitat modification of listed taxa. Given that monocots are at risk, there is the 

potential for habitat modification to indirectly affect all listed taxa.

The draft assessment will be published by EPA in the Federal Register for public review and 

comment.

Human Health Risk Assessment

EPA HED evaluated hazard and exposure data, as well as dietary, residential (non-occupational), 

occupational, and aggregate exposures to estimate the risk to human health that could potentially 

Page 8-18
result from the proposed new use of quizalofop on DAS-40278-9 corn. Based on their draft 

human health risk assessment, EPA HED recommends for a registration for the use of quizaolfop

on DAS-40278-9 corn. EPA identified additional data needed, specific tolerance 

recommendations, and label modifications. A summary of the results of the assessment are 

provided, below. The draft assessment will be published by EPA in the Federal Register for 

public review and comment.

Hazard Characterization: Quizalofop ethyl has low acute toxicities via the oral, dermal, and

inhalation routes. It is not an eye or dermal irritant nor a skin sensitizer. Following oral 

administration, quizalofop ethyl is rapidly absorbed and excreted via urine and feces. Liver is 

the target organ as evidenced by increased liver weight and histopathological changes in the 

liver.

There were no effects observed in oral toxicity studies that could be attributable to a single-dose 

exposure. Hence, a dose and endpoint have not been selected for assessment of acute exposure. 

Similarly, there was no observed toxicity in a dermal subchronic study at the highest dose tested 

(above the limit dose) so no dermal risk assessment is needed. Inhalation toxicity studies for 

occupational exposure assessment are waived based on the low exposure expected by the current 

and proposed use patterns. A chronic reference dose (cRfD) was established based on a 

combined chronic toxicity/carcinogenicity study in rats. Mutagenicity studies conducted on 

quizalofop ethyl did not demonstrate evidence of mutagenic potential. The Cancer Peer Review 

Committee determined that quizalofop ethyl should be classified as Category D (not classifiable 

as to human carcinogenicity). As such, a cancer risk assessment was not conducted.

Developmental studies in rats and rabbits and a two-generation reproduction study in rats 

showed no evidence (qualitative or quantitative) for increased susceptibility following in utero

and/or pre/post-natal exposure to quizalofop ethyl.

Dietary Exposure and Risk Assessment: An acute dietary risk assessment was not performed, as 

an acute endpoint was not identified in the hazard assessment. Similarly no cancer risk 

assessment was needed, as quizalofop ethyl was not classifiable with regard to carcinogenicity.

A chronic dietary exposure assessment was conducted using the maximum application rate per 

season for quizalofop ethyl on dry peas in Michigan. Under this scenario, children (1-2 years) 

were found to have the maximum chronic dietary risk at 29% of the chronic population adjusted 

dose (cPAD). This is well below HED’s level of concern of 100% of cPAD.

Residential Risk: Quizalofop ethyl has no registered homeowner or ornamental uses and none 

are being proposed. 

Aggregate Risk Estimates: Aggregate risk estimates take into account dietary and non-dietary

residential sources of exposure. As there are no registered or proposed uses of quizalofop that

would result in non-dietary residential exposure, the aggregate risk estimates are equivalent to

the chronic dietary risk estimates discussed above and are below HED’s level of concern.

Occupational Exposure and Risk Assessment: No doses or endpoints for dermal or inhalation 

exposure were selected or needed. Therefore, a quantitative estimate of occupational risk was not 

Page 8-19
determined. The acute toxicity categories are IV for both routes of exposure, and a 12-hour reentry interval (REI) was established under the worker protection standard (WPS).

Glufosinate Ammonium

Glufosinate is a contact herbicide which is taken up by the plant primarily through the leaves.

There is no uptake from the soil through the roots, presumably because of the rapid degradation

of glufosinate by soil microorganisms. There is limited translocation of glufosinate within the

plant.

Glufosinate is manufactured and labeled by Bayer Cropscience for pre-plant burndown on 

conventional or GE soybean, corn, cotton, canola, or sugar beet and post-emergence use on crops 

designated as LibertyLinkTM (soybean, corn, cotton, canola, and rice). The PAT protein 

expressed in DAS 68416-4 and DAS 44406-6 soybean soybean is similar to PAT found in other 

commercially-grown glufosinate-resistant crops (e.g., LibertyLinkTM soybeans, corn, cotton, 

canola, rice). Since the PAT protein has been included as an herbicide tolerance marker in 

products containing plant incorporated protectants (PIPs), it has been reviewed by EPA as a PIP 

inert ingredient (US-EPA, 2005a). Based on their environmental risk assessment, EPA 

determined that the PAT protein presents a low probability of risk to human health and the 

environment and granted an exemption from the requirement of a tolerance for this PIP inert 

ingredient (40 CFR 180.1151; 62 FR 17719, Aug. 11, 1997).

Based on pesticide usage data from USDA-NASS, private pesticide market research, and 

California Department of Pesticide Regulation (DPR), EPA estimated glufosinate usage from 

2003 through 2010. The crops with the highest glyphosate uses (based on average treated 

fraction of acreage) were: almond (15%), canola (25%), grapes (15%), and pistachios (20%). All 

other treated crops averaged less than 15% of the total acreage grown (US-EPA, 2012d).

DAS has indicated that the proposed glufosinate application rate for use on DAS-68416-4 

soybean and DAS 44406-6 soybean will be consistent with the current use pattern of glufosinate 

on other glufosinate-resistant soybean (i.e., LibertyLinkTM soybean) (DAS, 2010b). As there is 

no change from the current EPA-approved labeled use pattern, no petition has been submitted to 

EPA for a change in the glufosinate label. The EPA-approved label for LibertyTM (i.e., 

glufosinate ammonium) use on glufosinate-resistant soybean can be viewed here: 

http://www.bayercropscience.us/products/herbicides/liberty/labels-msds

The EPA-registered use of glufosinate on LibertyLinkTM soybean includes an initial burndown 

application of glufosinate no higher than 0.66 lb a.i./A (36 fl oz/A) with a minimum of 0.53 lb 

a.i./A (29 fl oz/A). A single second in-season application of glufosinate up to 0.53 lb a.i./A (29 

fl oz/A) is approved on LibertyLinkTM soybeans, with a seasonal maximum rate of 1.2 lb a.i./A 

(65 fl oz/A) permitted. Glufosinate applications on LibertyLinkTM soybean should be made from 

emergence up to but not including the bloom growth stage and within 70 days of harvesting.

Pesticide residue tolerances for quizalofop are listed in 40 CFR Part 180.473 (US-EPA, 2012c). 

As quizalofop is not currently approved by EPA for use on corn, only residue limits for soybean 

commodities are shown in Table 8-7, representing combined residues of combined residues of 

quizalofop ethyl, quizalofop, and quizalofop methyl.

Page 8-20
Table 8-7. 2,4-D Tolerances for Corn and Soybean Commodities

Commodity Residue (parts per million)

Corn, field, forage 4.0

Corn, field, grain 0.20

Corn, field, stover 6.0

Soybean 2.0

Soybean, hulls 0.02

Source: §180.473 Glufosinate ammonium; tolerances for residues (US-EPA, 2012c).

Currently, glufosinate is undergoing registration review by EPA. The registration review began 

in 2008 and a decision is expected in 2013 (US-EPA, 2009a). EPAs website for the glufosinate 

ammonium registration review case can be found here:

http://www.epa.gov/oppsrrd1/registration_review/glufosinate_ammonium/index.htm

The docket containing documents related to EPAs review can be viewed here:

http://www.regulations.gov/#!docketDetail;D=EPA-HQ-OPP-2008-0190

Page 8-21
References:

Burton, J.D., J.W. Gronwald, D.A. Somers, B.G. Gengenbach, and D.L. Wyse. 1989. "Inhibition 

of corn acetyl-CoA carboxylase by cyclohexanedione and aryloxyphenoxypropionate 

herbicides." Pesticide Biochemistry and Physiology 34: 76-85.

DAS.2012a. "Dow AgroSciences LLC Comments to Docket ID APHIS-2012-0019,." Section 2: 

Estimate of Herbicide Volume and Impact on Environmental Load of Herbicides with the 

Introduction of Enlist Soybean (DAS-68416-4). 66.

DAS.2011a. "EnlistTM Weed Control System - Technical Bulletin." Dow AgroSciences.

DAS. 2011b. EnlistTM Weed Control System - Technical Bulletin.

DAS.2012b. "EnlistTM Weed Control System." PowerPoint Slide Deck presented June 11, 2012 

to APHIS-BRS and Louis Berger Inc. staff,. Ed. Blewett, T.C. 68.

DAS.2011c. "GF-2654 TS Draft Label." Supplemental Information for Petition for 

Determination of Nonregulated Status for Herbicide Tolerant DAS-68416-4 Soybeans. 

Ed. Krieger, Mark S.: Dow AgroSciences LLC.

DAS.2011d. "Petition for Determination of Nonregulated Status for Herbicide Tolerant DAS444Ø6-6 Soybean." Ed. Mark, S. Krieger: Dow AgroSciences. 

228. http://www.aphis.usda.gov/brs/aphisdocs/11_23401p.pdf.

DAS. 2010a. Petition for Determination of Nonregulated Status for Herbicide Tolerant DAS40278-9 Corn. Submitted by L. Tagliani, Regulatory Leader, Regulatory Sciences & 

Government Affairs. Indianapolis, IN: Dow AgroSciences, LLC.

DAS.2010b. "Petition for Determination of Nonregulated Status for Herbicide Tolerant DAS68416-4 Soybean." Ed. Mark, S. Krieger: Dow 

AgroSciences. http://www.aphis.usda.gov/biotechnology/not_reg.html.

DAS.2012c. "Preliminary Plant Pest Risk Assessment and Draft Environmental Assessment for 

Determination of Nonregulated Status of DAS-68416-4 Soybean Genetically Engineered 

for Herbicide Tolerance." 9/11/2012 ed: Dow Agrosciences. 66.

DAS.2011e. "Research Demonstrating Reduction in Potential Off-Target Movement for 2,4-D 

Choline and Colex-DTM Technology as Part of the EnlistTM Weed Control System." 

Supplemental Information for Petition for Determination of Nonregulated Status for 

Herbicide Tolerant DAS-68416-4 Soybean. 13.

DAS. 2011f. Supplemental Information for Petition for Determination of Nonregulated Status 

for Herbicide Tolerant DAS-40278-9 Corn; Regulatory Overview of 2,4-D and 

Quizalofop Use on DAS-40278-9 Corn. Submitted by T.C. Blewett, Regulatory Leader, 

Regulatory Sciences & Government Affairs. Indianapolis, IN: Dow AgroSciences, LLC.

Page 8-22
Devine, M.D., and A. Shukla. 2000. "Altered target sites as a mechanism of herbicide 

resistance." Crop Protection 19: 881-89.

DuPont. 2010. "DuPontTM Assure® II Herbicide Label." 2010. Web. March 31 

2011 http://www.cdms.net/LDat/ld742006.pdf.

Henderson, A. M.; Gervais, J. A.; Luukinen, B.; Buhl, K.; Stone, D.2010. "Glyphosate Technical 

Fact Sheet." Ed. National Pesticide Information Center, Oregon State University 

Extension Services. 14. http://npic.orst.edu/factsheets/glyphotech.pdf.

Industry Task Force II. 2005. "2,4-D Research Data." 2005. Web. April 4 

2011 http://www.24d.org/background/Backgrounder-What-is-24D-Dec-2005.pdf.

Kelley, K.B., and D.E. Riechers. 2007. "Recent developments in auxin biology and new 

opportunities for auxinic herbicide research." Pesticide Biochemistry and Physiology 

89.1: 1-11.

Loux, M.M, D. Doohan, A.F. Dobbels, W.G. Johnson, G.R.W. Nice, T.N. Jordan, and T.T 

Bauman. 2011. Weed Control Guide for Ohio and Indiana, Bulletin 789, Pub # WS16: 

The Ohio State University Extension and Purdue University Extension.

Powles, S.B., and C. Preston. 2009. "Herbicide Cross Resistance and Multiple Resistance in 

Plants." Herbicide Resistance Action Committee 2009. Web. April 19 

2011 http://www.hracglobal.com/Publications/HerbicideCrossResistanceandMultipleResi

stance/tabid/224/Default.aspx.

Tu, M., C. Hurd, and JM Randall. 2001Weed Control Methods Handbook: Tools and Techniques 

for Use in Natural Areas. Ed. Conservancy, The Nature: UC Davis, CA.

US-EPA.2012a. "2,4-D (030001, 030004) - Screening Level Usage Analysis (SLUA)." Ed. 

Office of Chemical Safety and Pollution Prevention. Washington, D.C.: U.S. 

Environmental Protection Agency. Vol. 

2013. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0330-0007.

US-EPA.2013a. "2,4-D Final Work Plan - Registration Review Case Number 73." Ed. Office of 

Chemical Safety and Pollution Prevention. Washington, D.C.: U.S. Environmental 

Protection Agency. Vol. 2013 of Docket Number EPA-HQ-OPP-2012-

0330. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0330-0024.

US-EPA. 2011a. "40 CFR §180.142 2,4-D; Tolerances for Residues." Federal Register 76: 

55817. http://ecfr.gpoaccess.gov/cgi-bin/textidx?SID=226c82c0bcc9c7c05d8a42c3d942def8&node=40:25.0.1.1.27.3.19.19&rgn=div8

Page 8-23
US-EPA. 2010a. "40 CFR §180.364 - Glyphosate; tolerances for residues. ." U.S. 

Environmental Protection Agency July 1, 2010 2010a. Web. May 28, 2013 

2013 http://cfr.vlex.com/vid/180-364-glyphosate-tolerances-residues-19814904.

US-EPA. 2012b. "40 CFR §180.441 Quizalofop ethyl; tolerances for residues." Federal 

Register 77.23630,. http://www.ecfr.gov/cgibin/retrieveECFR?gp=1&SID=11dba60639a8b0b1e4cfe2d489b25cca&ty=HTML&h=L

&r=PART&n=40y25.0.1.1.27.

US-EPA. 2011b. "40 CFR §180.442 Quizalofop Ethyl; Tolerances for Residues." Federal 

Register 71.187: 56378.

US-EPA. 2012c. "§180.473 Glufosinate ammonium; tolerances for residues." Federal Register 

77.59113,. http://ecfr.gpoaccess.gov/cgi-bin/textidx?SID=ec73bf998f5c2e476a62b6f3e7e146ce&node=40:25.0.1.1.27.3.19.209&rgn=div

8.

US-EPA. 2005a. "Attachment III: Environmental Risk Assessment of Plant Incorporated 

Protectant (PIP) Inert Ingredients." U.S. Environmental Protection Agency 2005a. Web. 

July 20 

2011 http://www.epa.gov/scipoly/sap/meetings/2005/december/pipinertenvironmentalrisk

assessment11-18-05.pdf.

US-EPA.2013b. "EFED Registration Review Problem Formulation for 2,4-D - REVISED." Ed. 

Office of Chemical Safety and Pollution Prevention. Washington, D.C.: U.S. 

Environmental Protection Agency. 86. Vol. Docket EPA-HQ-OPP-2012-0330-

0025. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2012-0330-0007.

US-EPA.2012d. "Glufosinate (128850) Screening Level Usage Analysis (SLUA)." Ed. Office of 

Chemical Safety and Pollution Prevention. Washington, D.C.: U.S. Environmental 

Protection Agency. 2 of Docket Number EPA-HQ-OPP-2008-

0190. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2008-0190-0029.

US-EPA.2009a. "Glufosinate Final Work Plan Registration Review 2008." Ed. Office of 

Prevention, Pesticides, and Toxic Substances,. Washington, D.C.: U.S. Environmental 

Protection Agency. 8 of Docket Number EPA-HQ-OPP-2008-

0190. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2008-0190-0015.

US-EPA.2009b. "Glyphosate Final Work Plan (FWP) - Registration Review Case Number 

0178." Ed. Office of Prevention, Pesticides, and Toxic Substances,. Washington, D.C.: 

U.S. Environmental Protection Agency. 7 of Docket Number EPA-HQ-OPP-2009-

0361. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2009-0361-0042.

US-EPA. 2010b. "Pesticide Registration Manual: Chapter 11 - Tolerance Petitions." U.S. 

Environmental Protection Agency 2010b. Web. November 3 

2011 http://www.epa.gov/pesticides/bluebook/chapter11.html.

Page 8-24
US-EPA. 2010c. "Pesticide Registration Program." U.S. Environmental Protection Agency 

2010c. Web. June 30 2011 http://www.epa.gov/pesticides/factsheets/registration.htm.

US-EPA. 2009c. Registration Review- Preliminary Problem Formulation for the Ecological Risk 

and Drinking Water Exposure Assessments for Glyphosate and Its Salts (PC Code 

417300, 103601, 103604, 103607, 103608, 103613, 103603, 103605, 128501).

Washington, D.C. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP2009-0361-0007.

US-EPA. 2005b. Reregistration Eligibility Decision for 2,4-D. Washington: U.S. Environmental 

Protection Agency. http://www.epa.gov/oppsrrd1/REDs/24d_red.pdf.

US-EPA.2012e. "Updated Screening Level Usage Analysis (SLUA) Report in Support of 

Registration Review of Glyphosate." Ed. Office of Chemical Safety and Pollution 

Prevention. Washington, D.C.: U.S. Environmental Protection Agency. 4 of Docket 

Number EPA-HQ-OPP-2009-

0361. http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2009-0361-0045.

USDA-APHIS. 2010. Plant Pest Risk Assessment for DAS-40278-9 Corn. Riverdale, MD: US 

Department of Agriculture, Animal and Plant Health Inspection Service, Biotechnology 

Regulatory Services.

USDA-NASS. 2011. "Usage Search: State - All States/Areas; Year: All Years; Crop: All 

Crops; Agricultural Chemical: Quizalofop, ethyl." 2011. Web. April 19 

2011 http://www.pestmanagement.info/nass/.

Wright, T.R., G. Shan, T.A. Walsh, J.M. Lira, C. Cui, P. Song, M. Zhuang, N.L. Arnold, G. Lin, 

K. Yau, S.M. Russel, R.M. Cicchillo, M.A. Peterson, D.M. Simpson, N. Zhou, J. 

Ponsamuel, and Z. Zhang. 2010. "Robust crop resistance to broadleaf and grass 

herbicides provided by aryloxyalkanoate dioxygenase transgenes." Proceedings of the 

National Academy of Sciences of the United States of America 107.4: 20240-

5. www.pnas.org/cgi/doi/10.1073/pnas.1013154107.

Page 8-25