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)

The undersigned submits this information under 7 CFR 340.6 to support the determination that 

the article should not be regulated under 7 CFR 340.

Submitting Company:

Dow AgroSciences LLC

Submitted by:

__________________________________

T. Craig Blewett

Regulatory Leader

Regulatory Sciences & Government Affairs

Dow AgroSciences LLC

9330 Zionsville Road

Indianapolis, IN 46268

Telephone: (317) 337-4421

FAX: (317) 337-4649

tcblewett@dow.com

July 2, 2012
Supplemental Information for USDA Petition for Nonregulated Status of DAS-40278-9 Corn Page 2 of 16

Dow AgroSciences LLC

Summary

Dow AgroSciences (DAS) has submitted a petition to the United States Department of 

Agriculture (USDA)’s Animal and Plant Health Inspection Service (APHIS) for the 

determination of nonregulated status for DAS-40278-9 corn, which provides tolerance to the 

herbicides 2,4-dichlorophenoxy acetic acid (2,4-D) and quizalofop.

The deregulation of DAS-40278-9 corn will usher in a new era of weed control by improving 

existing weed control practices and introducing new modes of action in corn production. 

Various scenarios based on different input assumptions have been constructed to estimate 

potential volumes of 2,4-D, glyphosate and quizalofop on commercial corn hybrids that contain 

DAS-40278-9 and other herbicide tolerant traits. The projected environmental loading of 

herbicide use in response to the growing emergence of glyphosate resistant weeds as previously 

discussed is reviewed. Additionally, the ecological assessment of pesticides in light of new 

projected volumes is addressed from a regulatory perspective.
Estimate of Herbicide Volume and Impact on Environmental Load of

Herbicides with the Introduction of Enlist corn (DAS‐40278‐9)

Executive Summary 

The introduction of DAS-40278-9 corn (EnlistTM corn) and Enlist DuoTM herbicide will bring a 

much needed new herbicide tolerant trait and vastly improved herbicide technology into 

American agriculture. The new crop trait offers increased tolerance to 2,4-D as well as tolerance 

to the ‘fop’ family of herbicides, combining proven broadleaf weed control with a new mode of 

action for control of grassy weeds in corn. The new trait will be stacked with existing glyphosate 

tolerance traits to enable the continued use of the extremely popular and beneficial glyphosatetolerant technology and help prevent further emergence of glyphosate tolerant weeds. 

To accompany this new crop trait technology a new herbicide offering, featuring the novel 2,4-D 

choline salt, in a premix with glyphosate has been developed. Combining the features of the 

2,4-D choline salt with new developments in proprietary formulation and manufacturing science 

has resulted in a 2,4-D herbicide product with significantly reduced potential for drift and 

volatility as well as decreased odor and better handling properties. 

To first look at the herbicide rates used on a single acre, a recent study modeled several farms in 

the corn belt. (1) The study found that when the average Enlist Duo herbicide use rates were 

compared to the average use rates of all of the top alternate, currently available herbicides 

popular for controlling glyphosate-resistant weeds, the use of Enlist Duo on DAS-40278-9 corn 

would reduce the per acre environmental load of herbicides compared to these top, currently 

available, alternative programs. 

To realistically estimate the total 2,4-D volume increase across the country that may occur with 

Enlist and Enlist Duo, the following scenarios were developed based on realistic, yet very 

conservative (bias towards over-predicting) assumptions. 

Scenario 1 assumes growers will only apply Enlist Duo to DAS-40278-9 corn where 

growers are facing or actively trying to prevent the establishment of glyphosate-resistant 

weeds. Additionally this also assumes that all farmers with corn acres that have 

glyphosate resistant weeds will plant DAS-40278-9 corn and will use Enlist Duo 

herbicide. The projections indicate an approximate six-fold increase in 2,4-D use in 2020 

compared to the volume of 2,4-D currently used on conventional corn. 

Scenario 2 assumes that all acres of DAS-40278-9 corn would receive applications of 

Enlist Duo, regardless of weed control need, and thus relies on estimates of the projected 

market share of DAS-40278-9 corn. These projections estimate an approximately 8X 

increase in 2,4-D use compared to what is currently used on conventional corn. 
Scenario 3 assumes that all current glyphosate-tolerant corn acres would be planted to 

hybrids that also contain the DAS-40278-9 trait. This is an unrealistically high 

estimation but provides an upper confidence level on 2,4-D volume. Even with this 

extreme assumption, the estimated 2,4-D volume is only a 17-fold increase in 2,4-D use 

on corn compared to the current use of 2,4-D on conventional corn 

Some projections in the comments and press have suggested increases in volume of 100’s to 

even 1000 fold. When actual use patterns and market dynamics are taken into consideration, 

more reasonable projections are only a 6-8 fold increase, with an extremely conservative 

estimate of only17-fold. 

Introduction of New Technology 

A new herbicide product, to be commercialized as Enlist Duo, is currently under regulatory 

review at the Environmental Protection Agency (EPA or the Agency)1

. This product, when 

approved, will be marketed for use on DAS 40278-9 corn. Enlist Duo is a proprietary pre-mix of 

2,4-D choline and glyphosate DMA and contains Colex-DTM Technology. Prominent attributes 

of this technology are a greatly reduced volatility and drift profile, very low odor and better 

handling characteristics (MRID 48862902 and 48844001). Enlist Duo is formulated as an 

approximate 1:1 ratio of 2,4-D choline:glyphosate DMA. Use directions for Enlist Duo have 

been well described in the draft Environmental Assessment for DAS 40278-9 corn and 

documents previously submitted by DAS to EPA and USDA. 

The new use directions under consideration by EPA will allow a pre-emergent (burn down) 

application of 0.5-1 lb acid equivalents/acre (ae/ac) of 2,4-D (and glyphosate) and up to two 

applications (0.5-1 lb 2,4-D ae/ac each, and glyphosate) post-emergent through the V8 stage or 

48” tall corn. Total seasonal use is limited to a total of 3 lbs 2,4-D ae/ac/season, identical to the 

current seasonal maximum use of 2,4-D on conventional (non-Enlist) corn. DAS-40278-9 corn 

will also tolerate applications of the herbicide quizalofop. 

__________________________ 

1

   EPA published a Notice of Receipt on May 23, 2012, opening up a comment period that ends on June 22, 

2012. See 77 Fed. Reg. 30524, 30526 (May 23, 2012) (“Active ingredient: 2,4-D choline salt.) Proposed 

Classification/Use: Enlist AAD–1 Corn (Trait Code: DAS–40278–9)”).
Current 2,4-D Use on Corn 

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. 

 Estimates of US corn acreage from private and public sources ranges from 92MM acres to 

approximately 96 MM acres. Current corn acreage is estimated by USDA at approximately 96 

million acres (http://www.nass.usda.gov/Newsroom/2012/03_30_2012.asp ). 2,4-D is currently 

used on approximately 8% of the corn acres with a recent historical range from 8%-14% of corn 

acreage according to USDA estimates (Plant Pest Risk Assessment; 

www.aphis.usda.gov/brs/aphisdocs/09_23301p_dpra.pdf ). When 2,4-D is utilized in a burn 

down or pre-plant treatment, 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 

(http://www3.ag.purdue.edu/btny/weedscience/Documents/BurndownMadness.pdf). 2,4-D is 

currently labeled for a single post-emergent application at 0.5 lbs ae/ac. While current estimates 

of 2,4-D volume used on corn are not readily available in a public format, third party proprietary 

data (data not submitted) estimated in 2011that 5.5 million pounds of 2,4-D were applied to 9.5 

million acres for an average of 0.57 lbs ae/treated acre. This is up rather sharply from 2009 

when 4 million pounds were used on 7.3 million acres. This increase in 2,4-D use may be driven 

by farmers seeking non-glyphosate weed control options to control glyphosate-resistant and/or 

hard to control weeds. 

Current Glyphosate Use on Corn 

Current glyphosate use directions approved by EPA for use on glyphosate-tolerant 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. 

Third party proprietary market research data indicate that the percentage of glyphosate-tolerant 

corn acres has grown over the last four years (Table 1). Total pounds of glyphosate applied to 

corn have also increased during this time (along with 2,4-D use, as mentioned above). There is a 

slight but increasing trend in both the rate of glyphosate applied per acre as well as the total 

number of applications made per acre. These increases reflect the fact that farmers are 

continuing to adopt glyphosate-tolerant corn for its many cultural, agronomic and economic 

benefits even with the growing presence of glyphosate resistant and hard to control weeds. 
Table 1. Glyphosate Use on Glyphosate Tolerant 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

From third party proprietary data 

Changes in 2,4-D and Glyphosate Use Directions for Enlist Duo Herbicide 

Enlist DuoTM Herbicide was designed to fit with the existing EPA-approved glyphosate use 

pattern which has resulted in many benefits including reduced erosion and runoff. Glyphosate is 

expected to remain a core post-emergent herbicide due to these benefits, as well as its broad 

spectrum of weed control. Use directions for Enlist Duo were developed to directly overlap with 

the glyphosate use pattern on corn, so that farmers who currently use glyphosate will find it 

extremely easy to use Enlist Duo on DAS-40278-9 corn. 

As described above, Enlist Duo herbicide is an approximate 1:1 premix of 2,4-D choline and 

glyphosate DMA, based on acid equivalents. By using Enlist Duo herbicide on DAS_40278-9 

corn, glyphosate use would be: 

 A single 1.0 lb glyphosate ae/ac application made pre-emergence; 

 Up to two post-emergent applications each at 1.0 lbs glyphosate ae/ac. 

While DAS-40278-9 corn growers could make additional glyphosate applications, up to the 

seasonal maximum allowed on glyphosate labels, Dow AgroSciences (DAS) anticipates that 

additional glyphosate applications would be unlikely due to Enlist Duo’s improved weed control, 

the growing use of foundational herbicide (preplant) programs, and the adoption of other 

products with additional modes of action. 

The EPA-approved label directions for use of 2,4-D on corn currently allows a single pre-plant 

application of up to 1.0 lbs ae/ac. A single post-emergent application of 0.5 lbs ae/ac can be 

applied. This application can be broadcast if the corn is less than 8” tall. Drop nozzles should be 

used if the corn is greater than 8” to avoid injury to the corn crop. A single pre-harvest 

application of 1.5 lbs ae/ac can be made after corn is physiologically mature (denting). 

With the Enlist Weed Control System and use of Enlist Duo herbicide, 2,4-D choline use on 

DAS-40278-9 corn would be: 

 A single 1.0 lb 2,4-D ae/ac application made pre-emergence; 
 Up to two post-emergent applications each at 1.0 lbs 2.4-D ae/ac. 

Thus, use of Enlist Duo herbicide would provide for a total seasonal use of up to 3 lbs ae/ac of 

2,4-D choline (or 6 lbs ae/ac of both 2,4-D and glyphosate actives) on DAS 40278-9 corn 

(Figure 1). 

Quizalofop Use on Corn 

Quizalofop is an aryloxyphenoxypropionate (Fop) grass selective herbicide that is used to control 

a broad list of grassy weeds, sedges and some broadleaf weeds. Corn is a member of the grass 

family and as such is extremely sensitive to quizalofop with minute quantities causing severe 

injury or death to conventional corn plants. DAS 40278-9 corn is tolerant to quizalofop at 

current commercial application rates used for broadleaf crops. 

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. DAS anticipates that the 

primary use of quizalofop initially will be as a selection agent, to remove (kill) any corn plants in 

the seed propagation nursery that do not contain the DAS 40278-9 trait. This helps to ensure a 

high degree of purity in corn bred to contain the trait as all corn plants not containing the trait 

would be eliminated. 
Tolerance to quizalofop also brings a new mode of action for the control of grassy weeds in corn. 

Glyphosate is a strong grass herbicide but reports in the science literature indicate that six grass 

species have developed resistance to glyphosate in the US (Jungle rice, Goose grass, Italian 

Ryegrass, Rigid Ryegrass, Annual Ryegrass and Johnson grass). The amount of acres infested 

with these glyphosate-resistant grasses has been published (~31000 ac) but there is uncertainty 

about the estimation accuracy (http://www.weedscience.org/In.asp). With the exception of 

Italian Ryegrass and Rigid Ryegrass the acreage thought to be involved is small and located in 

the southern US and California. Quizalofop offers a new mode of action to control these 

glyphosate resistant grasses. 

Changes in Quizalofop Use Directions with Enlist Weed Control System 

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. The primary anticipated use at this 

time would be as a selection agent in corn nurseries to select out (kill) those plants that do not 

contain the AAD-1 gene. EPA’s approval of the registration amendment would also allow 

quizalofop to be used as a post emergent grass herbicide on DAS-40278-9 corn. 

Whether used as a selection agent or as a 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. 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. 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. Soybeans currently represent a 

significant post-emergent use of quizalofop. It is important to note that soybeans are often 

grown rotationally with corn so the introduction of quizalofop use on corn would not represent a 

significant new geography for quizalofop use. 
2,4-D Choline and Glyphosate proposed Use on DAS 40278-9 Corn 

Third-party proprietary market research demonstrates that approximately 90% of glyphosatetolerant corn acres receive at least one glyphosate application. Interestingly, significant 

populations of farmers (~10%) that purchase glyphosate tolerant corn elect not to make a postemergent glyphosate application. The market research also indicates that only 22% of planted 

corn acres currently receive a burn-down (pre-plant or pre-emergence) herbicide application. 

Utilizing the historically consistent data from the current and broad use of glyphosate on corn, 

DAS has estimated that farmers who grow DAS-40278-9 corn will use an average of 0.875 lbs 

2,4-D ae/ac/application with an average of 1.33 applications1

 per season. The application rate 

(0.875 lbs 2,4-D ae/ac) is the midpoint between the medium and high rates allowed on the Enlist 

Duo label and is consistent with the glyphosate rate needed for weed control. 

Estimating total acres of DAS-40278-9 corn planted and the use of Enlist Duo herbicide on that 

corn has many inherent accuracy limitations, and it is difficult, if not impossible, to make any 

such predictions with certainty. Nevertheless, DAS has derived three scenarios to estimate the 

potential use of 2,4-D in DAS-40278-9 corn after deregulation and commercialization: 
2,4-D: Scenario One. The first scenario assumes that growers will only apply Enlist Duo to 

DAS-40278-9 corn where growers are facing or actively trying to prevent the establishment of 

glyphosate-resistant weeds. Additionally this also assumes that all farmers with corn acres that 

have glyphosate resistant weeds will plant DAS-40278-9 corn and will use Enlist Duo herbicide 

(a very aggressive assumption due to other weed control options available). Using third party 

market data, DAS has estimated that 5% of US corn acreage had glyphosate resistant weeds in 

2010, and that the percentage would grow to 10% of corn acreage by 2015 and to 30% by 2020 

(Figure 2). This is consistent with but less aggressive than predictions made by other others, (see 

Foresman, Figure 2). 

Figure 2. Projected corn and soybean acres infested with glyphosate resistant weeds. 

Sources:   

 Foresman, C. 2009.  Syngenta Resistance FighterTM Message Board.  http://blog.syngenta‐

us.com/blogs/ask_the_expert/archive/2009/04.aspx  Accessed January 16, 2011.  

 Dow AgroSciences LLC.

0

5

10

15

20

25

30

35

40

Millions of Aces

Syngenta Dow
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 

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: 

92MM acres x 30% resistant weeds (in 2020) x .875 lbs ae/ac/application x 1.33 

applications/season = 31MM lbs 2,4-D ae per year. This represents an approximate sixfold increase in 2,4-D use in 2020 compared to the volume of 2,4-D currently used on 

conventional corn. 

2,4-D: Scenario Two. The second scenario assumes, for purposes of this discussion, that all 

acres of DAS-40278-9 corn would receive applications of Enlist Duo, regardless of weed control 

need, and thus relies on estimates of what the projected market share of DAS-40278-9 corn will 

be: 

DAS sells corn 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, markets for which DAS-40278-9 corn could be introgressed. 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. However, for purposes 

of this estimate, 5% will be used as a minimum potential DAS-40278-9 corn acreage. 

DAS is interested in and is pursuing licensing agreements with additional corn seed companies to 

breed DAS-40278-9 corn into a licensee’s corn germplasm. To date, no licensing agreement has 

been made. Through natural growth and licensing arrangements it is reasonably possible that, at 

maturity, approximately 45% of the corn germplasm could have the Enlist trait. For the purposes 

of this estimation, licensing contracts will be assumed with seed companies having 40% of the 

market. Together with DAS’s market share, for purposes of this estimate, we therefore assume 

DAS-40278-9 corn could ultimately be bred into corn hybrids planted on up to 45% of the total 

corn acreage. 

Due to the technical aspects of corn seed breeding, rapid improvement of germplasm and 

stacking with other traits, this level of adoption of DAS-40278-9 corn is estimated to take 5-10 

years to reach maturity (maturity in 2018-2023), which is consistent with other current herbicide 

tolerant traits. 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. 
Utilizing the data and assumptions stated in this scenario, the estimated range of acreage and 2,4-

D volume can be estimated as follows: 

Low: 92MM acres x 5% market share x 90% estimated 2

 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 lbs 2,4-D ae per year. This represents a slight decrease to essentially no 

change in 2,4-D volume compared to current use on corn. 

High: 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. This represents approximately an 8X increase in 2,4-D 

use compared to what is currently used on conventional corn. 

2,4-D: Scenario Three: The third scenario assumes that all current glyphosate-tolerant corn 

acres would be planted to hybrids that also contain the DAS-40278-9 corn trait. This is an 

unrealistically high estimation but provides an upper confidence level on 2,4-D volume. DAS40278-9 corn will be stacked with a glyphosate tolerant trait but it is impractical to assume that 

all glyphosate tolerant traits will be stacked with DAS-40278-9 corn due to competing offerings 

by other seed companies and the likelihood of other herbicide-tolerant corn options. 

Nevertheless, from Table 1, 82MM acres of the 92 MM total corn acres are planted to glyphosate 

tolerant 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 tolerant 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. This represents a 17-fold increase in 2,4-D use on corn compared to 

the current use of 2,4-D on conventional corn. 

Quizalofop Proposed Use on DAS 40278-9 Corn 

There are two major considerations in predicting the use of quizalofop on DAS 40278-9 corn: 

Use as a selection agent in producing hybrid seed corn, and use as a herbicide to control 

glyphosate resistant grasses. 

__________________________ 

2     Estimates based on current glyphosate application information.  The Enlist DuoTM application window with DAS‐

4078‐9 corn is consistent with the current glyphosate application window.
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. An additional 

refinement is that not all rows would be treated depending upon whether the trait is carried on 

the male or female parent. The range would be 20%-80% of the nursery field would be treated 

with quizalofop. For the purposes of this exercise we will use 80%. Two scenarios will be 

presented, both using the same assumptions as described above for 2,4-D use on DAS 40278-9 

corn. 

Quizalofop Use in Seed Corn: Scenario 1: This scenario uses DAS’ current 5% market share 

for field and silage corn. 

92MM acres /125 acres nursery/acre of field corn x 5% market share x 80% estimated 

DAS-40278-9 corn nursery acres treated x 0.082 lbs ai/ac/application x 1 application = 

2,415 lbs quizalofop. 

Quizalofop Use in Corn Seed Production: Scenario two: The second quizalofop scenario 

assumes a total of 45% of the market share contains the trait. 

92MM acres /125 acres nursery/acre of field corn x 45% market share x 80% estimated 

DAS-40278-9 corn nursery acres treated x 0.082 lbs ai/ac/application x 1 application = 

21,730 lbs quizalofop. 

Control of glyphosate-resistant grasses: As indicated above six species of grasses have 

developed resistance to glyphosate. Only Italian Ryegrass and Rigid Ryegrass have what could 

be considered substantially infested acreage: 10,000 acres of Italian Ryegrass in Arkansas and 

Mississippi each and 10,000 acres of Rigid Ryegrass in California. All other species infest <100 

acres per species, mostly in the Southern US or California. None of the grasses appear in 

significant corn growing regions but for the purposes of this exercise we will assume that all 

31000 acres are in corn growing acres and those growers will use quizalofop to control these 

weeds: 

Quizalofop Use in Field Corn: Scenario three: This scenario assumes that quizalofop will be 

used on all 31,000 acres of glyphosate resistant grasses. 

31M acres x 0.082 lbs ai/ac = 2,542 lbs quizalofop. 
Environmental Loading of Herbicides Used on Corn 

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 and 

DAS-68416-4 soybeans. 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 (1). 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. While the range of rates of these currently 

available alternate programs and the ones for Enlist programs overlapped, when the average of 

the Enlist 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. As discussed in 

the draft EA, no evidence supports any increase in total corn acreage planted as a result of 

deregulation of DAS-40278-9 corn. 

Ecological Assessment of Herbicide Use on Corn 

The EPA is the regulatory agency responsible for the review and approval or denial of all 

pesticide registrations. It is a violation of federal law for pesticides to be sold or distributed 

without an EPA registration. The Agency uses a risk assessment process in its registration 

decisions, evaluating risk based on exposure and hazard, for both humans and ecological 

organisms. EPA cannot register the use of a pesticide, or amend an existing registration to add a 

new use, unless the use of the pesticide meets the statutory “no unreasonable adverse effects” 

standard, i.e., EPA can only register new pesticides or pesticide uses if the use of that pesticide in 

accordance with the EPA-approved label will cause no unreasonable adverse effects on human 

health or the environment. 

In order to make its registration decisions, the Agency develops exposure assessments that 

characterize the potential environmental exposures that may result from the use of a pesticide. 

EPA uses the results of environmental fate studies, in combination with modeling work and 

pesticide use information to characterize the environmental fate of the pesticide in question. 

The Agency also uses modeling work to conservatively predict potential impacts on surface and 

ground water. This modeling work is used not only for environmental risk evaluations but is 

also an input parameter into dietary risk evaluations for humans (providing the drinking water 

component for dietary assessments). 

The results of the environmental fate work enable EPA to determine where a pesticide and its 

metabolites and degradates will go in the environment (air, water, soil), how long they will 
persist, and in what quantities. Based on study, model, and use information, the Agency then 

develops estimated environmental concentrations (EECs), which are compared to the toxicity 

endpoints of ecotoxicology studies for risk assessment purposes. EEC values are based on the 

maximum allowable application rate(s) for a pesticide even though typical application rates are 

lower than the maximum. 

As in the case of risk assessments for humans, EPA scientists use the most sensitive toxicity 

endpoints for ecotoxicology studies for risk assessment purposes. Using EECs based on 

maximum application rates and the most sensitive toxicity endpoints ensures that EPA risk 

assessments for wildlife are conservative and protective. 

EPA uses risk quotients (RQ’s) and levels of concern (LOC) for acute and chronic risk to 

wildlife to quantify and characterize risk assessments for plants and animals. RQ’s are ratios of 

EEC values over toxicity endpoints. The Agency uses different LOCs for non-endangered and 

endangered species. If planned use rates and use techniques result in RQ values that exceed 

LOCs, EPA may conduct a more refined risk assessment to better characterize risk. The Agency 

also considers how to mitigate potential risks, which may require changes in application rates 

and techniques, or may otherwise limit the use of the pesticide. 

EPA assessments of potential impacts on wildlife and the environment are designed to be 

conservative and protective. The Agency wants to be cautious in its assessments and would 

rather overstate than understate risk concerns. Each intended use pattern (e.g., corn, soybeans, 

consumer use) is evaluated. Agency environmental and ecological assessments are designed to 

cover each particular use of a pesticide (e.g., corn) regardless of whether all corn acreage is 

treated or only a portion of the acreage is treated (much more typical). Thus, even if the percent 

crop treated increases, the EPA assessments are still valid. 

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 resounding denial of that petition, affirming that 

2,4-D posed no unreasonable risk when used as directed (2). 

Summary 

The introduction of the Enlist Weed Control System and Enlist Duo herbicide will provide a 

much needed additional weed control tool to corn farmers in American agriculture. The Enlist 

Weed Control System offers a novel mechanism to offer, at the same time, multiple modes of 

action which has been cited by the National Academy of Sciences and the Weed Science Society 

of America as key components to an effective resistant weed management plan. The 

introduction of herbicide tolerant crops has helped enable the growing practice of no-till 

agriculture which has resulted in dramatic reductions in soil loss through erosion, made farming 
much more efficient, reduced trips across the field with resultant fuel and equipment savings, and 

enabled farmers to proficiently farm more acres (1). 

This exercise depicts the current use of 2,4-D in conventional corn and the expanded use of 2,4-

D choline introduced in Enlist Duo herbicide with the adoption of Enlist corn and the Enlist 

Weed Control System. Additionally, estimates on the use of quizalofop in DAS-40278-9 corn 

are portrayed. While growers will get improved weed control performance they will also benefit 

from the additional attributes of Enlist Duo herbicide, particularly the reduction in off-target 

movement potential via drift or volatility. These improvements help keep the herbicide on the 

treated field, further reducing risk to the environment and ecological organisms. 

1. Public Interest Document Supporting the Registration of 2,4-D and Quizalofop on 

Herbicide Tolerant DAS-40278-9 Corn and 2,4-D on Herbicide Tolerant DAS-68416-4 

Soybeans to Improve the Performance of Current Weed Control Systems, Provide 

Increased Weed Resistance Management Options, and Help Sustain the Widely Adopted 

Glyphosate Tolerant Cropping System that Helps Make Farming Easier, More Affordable 

and More Environmentally Beneficial. MRID 48535501. 

2. EPA Denies Petition on 2,4-D Pesticide 

http://www.epa.gov/oppfead1/cb/csb_page/updates/2012/2-4d-petition.html.