Supplemental Information for USDA Petition for Nonregulated Status of DAS-40278-9 Corn Page 1 of 50

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Supplemental Information for Petition for Determination of Nonregulated Status 

for Herbicide Tolerant DAS-40278-9 Corn

Economic and Agronomic Impacts of the Introduction of DAS-40278-9 Corn on 

Glyphosate Resistant Weeds in the U.S. Cropping System

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, Ph.D.

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

May 11, 2011
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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.

This document provides information pertaining to the economic and agronomic impact of 

DAS-40278-9 corn. This information includes: 

o Benefits of Glyphosate Tolerant Crops

o Weed Management in Glyphosate Tolerant Corn and Soybeans

o Long-term Weed Resistance Management through Use of Herbicide Tolerant 

DAS-40278-9

o Economic Benefits of Dow AgroSciences Herbicide Tolerant Technology

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

Soybeans on the Cost and Environmental Load of Herbicides Applied on 

Glyphosate Tolerant Corn and Soybeans 
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Economic and Agronomic Impacts of the 

Introduction of DAS-40278-9 Corn on Glyphosate 

Resistant Weeds in the U.S. Cropping System
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TABLE OF CONTENTS

1.1 Introduction_____________________________________________________________ 8

1.2 Glyphosate tolerant crop Technology Adoption ______________________________ 9

1.3 Factors Influencing Glyphosate tolerant crop Techology Adoption _____________ 10

2 Benefits of Glyphosate Tolerant Crops _______________________________________ 12

2.1 Environmental Benefits_________________________________________________ 12

2.1.1 Enables conversvation tillage with Glyphosate tolerant crops ________________ 12

2.1.2 Reduces soil erosion __________________________________________________ 13

2.1.3 Reduces greenhouse gas emission _______________________________________ 13

2.2 Economic Benefits _____________________________________________________ 14

2.2.1 Reduces chemical costs________________________________________________ 14

2.2.2 Reduces fuel costs ____________________________________________________ 14

2.2.3 Reduces labor costs___________________________________________________ 15

2.2.4 Reduces management costs ____________________________________________ 15

2.2.5 Global economic benefits ______________________________________________ 16

2.3 Yield Enhancement ____________________________________________________ 16

2.4 Convenience __________________________________________________________ 17

3 Weed Management in Glyphosate Tolerant Corn and Soybeans __________________ 19

3.1 Herbicide resistance____________________________________________________ 20

3.2 Other shifts in weed communities_________________________________________ 22

3.3 Potential for future spread of glyphosate resistant and hard-to-control weeds in 

glyphosate tolerant crops __________________________________________________ 23

3.4 Growers’ response to glyphosate resistant and hard-to-control weeds __________ 28

3.5 Weed management strategies to sustain glyphosate resistant cropping systems in 

corn and soybeans ________________________________________________________ 34

3.6 New tools for weed resistance managmenet ________________________________ 35

4 Long-term Weed Resistance Management through Use of Herbicide Tolerant DAS40278-9 ___________________________________________________________________ 36

4.1 DAS-40278-9 corn enables use of alternative modes of action to glyphosate ______ 36

4.2 Management of glyphosate resistance and hard-to-control weeds using herbicide 

tolerant DAS-40278-9 corn _________________________________________________ 37

4.3 Proposed Use Pattern and Compatibility with Glyphosate Cropping System_____ 39

4.4 Proactive resistance management for 2,4-D through integration with glyphosate _ 40

5 Economic Benefits of Dow AgroSciences herbicide tolerant technology___________43
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6 Impact of 2,4-D on Herbicide Tolerant DAS-40278-9 Corn and DAS-68416-4 

Soybeans on the Cost and Environmental Load of Herbicides Applied on Glyphosate 

Tolerant Corn and Soybeans to Control Glyphosate Resistant and Glyphosate Tolerant 

Weed Biotypes___________________________________________________________ 44

 Conclusions_____________________________________________________________ 44
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FIGURES

Figure 1.1 Adoption rates of herbicides tolerant corn and soybean in the United States__ 9

Figure 1.2 U.S. glyphosate prices______________________________________________ 11

Figure 2.1 Corn and soybean fuel consumption by tillage type, Central Corn Belt _____ 15

Figure 2.2 Benefits of glyphosate tolerant crops _________________________________ 18

Figure 3.1 Global reports of herbicide resistance weeds ___________________________ 20

Figure 3.2 Adoption of glyphosate tolerant crops and development of glyphosate resistant 

weeds in the United States ___________________________________________________ 21

Figure 3.3 Glyphosate Resistant Weeds ________________________________________ 24

Figure 3.4 Projected corn and soybean acres infested with glyphosate resistant broadleaf 

and grass weeds in the United States (excluding volunteer glyphosate resistant corn). __ 27

Figure 3.5 Average postemergence glyphosate use rates on corn and soybeans in the 

United States ______________________________________________________________ 28

Figure 3.6 Average number of glyphosate applications on corn and soybeans in the United 

States (includes burndown uses) ______________________________________________ 29

Figure 3.7 Total pounds of glyphosate applied on corn and soybeans in the United States

(includes bourndown uses) ___________________________________________________ 29

Figure 3.8 Preemergence non-glyphosate herbicide usage on glyphosate tolerant corn _ 31

Figure 3.9 Preemergence non-glyphosate herbicide usage on glyphosate tolerant soybeans

__________________________________________________________________________ 31

Figure 3.10 Post-emergence non-glyphosate herbicide usage on glyphosate tolerant corn32

Figure 3.11 Post-emergence non-glyphosate herbicide usage on glyphosate tolerant 

soybeans (excludes products typically used to control volunteer corn) _______________ 32

Figure 4.1 2,4-D, quizalofop, and glyphosate applications schedules for DAS-40278-9 Corn

__________________________________________________________________________ 40
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TABLES

Table 1.1 Year of deregulation for Glyphosate tolerant crops ______________________ 10

Table 1.2 Percent of all soybeans planted to herbicide tolerant varieties by state ______ 12

Table 3.1 Weeds that evolved resistance to glyphosate in glyphosate tolerant crops in the 

United States ______________________________________________________________ 22

Table 3.2 Weeds reported to have increased in abundance in glyphosate tolerant crops 25

Table 3.3 Future assumptions for glyphosate resistant weeds in corn and soybeans in the 

United States ______________________________________________________________ 26

Table 3.4 Future assumptions for glyphosate resistant weeds in corn and soybeans in the 

United States, Syngenta Corporation __________________________________________ 27

Table 3.5 Assessment of resistance risk by evaluation of the cropping system _________ 35

Table 4.1 Glyphosate resistant, ALS resistant weeds, and hard-to-control weeds that are 

controlled by 2,4-D _________________________________________________________ 38
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1 Economic and Agronomic Impacts of the Introduction of DAS-40278-9 Corn on 

Glyphosate Resistant Weeds in the U.S. Cropping System

1.1 Introduction

Glyphosate tolerant cropAtechnology has driven dramatic changes in agricultural 

production processes while generating important economic and environmental benefits. 

But as some agronomists warned, the benefits of glyphosate tolerant crops are beginning 

to be eroded by increasing weed resistance as well as weed population shifts to hard-tocontrol weeds. Growers have begun to alter production practices to adjust for weed 

resistance and shifts to hard-to-control weeds. Unfortunately, some of these practices, 

particularly tillage, reverse some of the benefits gained from glyphosate tolerant crop

technology. In order to preserve the benefits of glyphosate tolerant crop technology, 

Dow AgroSciences' herbicide tolerant DAS-40278-9 corn complements glyphosate 

tolerant crop technology by controlling glyphosate resistant and hard-to-control weeds 

without additional tillage. In addition, DAS-40278-9 corn provides another mode of 

action which is strongly suggested by agronomists as a best management practice in 

dealing with glyphosate resistant and hard-to-control weeds. 

The purpose of this paper is to demonstrate the importance of glyphosate tolerant crop

technology, briefly summarize the benefits of glyphosate resistant crop technology, 

describe the developing weed resistance and weed shift problem, discuss current 

solutions to weed resistance, provide an overview of Dow AgroSciences’ herbicide 

tolerant DAS-40278-9 corn, and finally document how this technology complements 

glyphosate tolerant crop technology and provides a durable, long-term solution to the 

development of weed resistance.

 

A

The following definitions are applied throughout this document:

Herbicide Tolerant Crop: A crop plant that has been developed (using techniques such as genetic 

engineering or selection of variants produced by tissue culture or mutagenesis) to survive and reproduce 

after treatment with a specific herbicide or herbicides that would normally damage an unmodified crop.

Herbicide Resistant Weed: A herbicide-resistant weed is a member of a population within a species that 

has an inherited ability to survive and reproduce following exposure to a dose of a herbicide normally lethal 

to susceptible populations of the species. Through repeated herbicide selection, the resistant population 

becomes dominant in a given area. 

Hard-to-Control Weed: A weed species that is inherently able to withstand treatment with a herbicide as 

a result of natural factors not involving herbicide selection or genetic mutation. 
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1.2 Glyphosate tolerant crop Technology Adoption

There are few technologies that have been as widely and universally adopted as 

glyphosate tolerant crops. USDA estimates that 91 percent of the soybeans planted in 

2009 were glyphosate tolerant varieties (see Figure 1.1).

1

 At least one other source, 

which surveys approximately 5,000 large U.S. farms, suggests similar results.2 In the 

case of corn, there is some discrepancy in the data on the percent of corn acres that were 

planted with glyphosate tolerant seed in 2009. USDA estimates that total herbicide 

resistant hybrids planted represented 68 percent of the corn acres planted in 2009.

1

 

Estimates from proprietary surveys and Monsanto (based on seed sales) are higher, 

exceeding 80% of total planted area.2,3 In any case, the prevalence of glyphosate tolerant 

seed use in both corn and soybeans is very high, underscoring the importance of

glyphosate tolerant technology.

Figure 1.1 Adoption rates of herbicide tolerant corn and soybeans in the United 

States

Sources: USDA's June "Acreage" Report, various issues, 2000-20091, Fernandez-Cornejo & McBride 

soybeans 1996-19994, Duke and Powles corn 1998-19995.

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

19961997199819992000200120022003200420052006200720082009

Percent of Planted Acres

Soybeans Corn
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1.3 Factors Influencing Glyphosate tolerant crop Technology Adoption 

The historical data on glyphosate tolerant technology releases and the rate of adoption 

provides informative clues about the perceptions of benefits, the ease of adoption, and the 

general availability of the technology. Adoption of most new technologies starts off 

slowly. Early adopters usually figure out if the technology lives up to claims made about 

it as well as how difficult the technology is to implement in the production process. In 

addition, availability of the technology can limit initial growth. Beyond this point the 

factors influencing adoption become more crop specific. It is also important to note that 

glyphosate tolerant crop technology was not simultaneously introduced for all crops in 

the same year and subsequently adoption curves start at different points (see Table 1.1). 

The literature from the late 1990's casts glyphosate tolerant technology mostly as a tool to 

enable easier management of crops: some early studies even documented yield drag in 

soybeans. 6 Yet in these early studies, the yield results were based on strip trials made in 

weed free fields which were not necessarily representative of actual farm conditions.6In 

addition, glyphosate tolerant technology was not available in the highest yielding soybean 

varieties at the time. USDA noted that analysts expected yield drags to disappear when 

the glyphosate tolerant trait was backcrossed into higher yielding parent lines.6 Despite 

the early concerns of a yield drag, the rapid adoption of glyphosate resistant crops 

indicates the value farmers associated with the new technology.

Table 1.1 Year of deregulation for glyphosate tolerant crops

Source: Duke and Powles, 2008.5

By 1998, adoption of glyphosate tolerant technology in soybeans had increased, jumping 

from 17 to 44 percent of total soybean acreage in the United States in just one year from 

1997 to 1998 (see Figure 1.1). This rapid jump in adoption suggests that growers 

perceived substantial benefits from adopting the technology. Studies document that 

glyphosate tolerant technology provided "better, simpler, cheaper, and more flexible 

weed management than the conventional alternatives."5, 7, 8, 9 There appears to be a 

reversal in tolerant technology adoption in 2000 for corn and soybeans (see Figure 1.1). 

However, this is probably more attributable to a shift in data sources on adoption rates 

Crop Year

Soybeans 1996

Canola 1996

Cotton 1997

Corn 1998
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rather than a reversal in adoptions rates for glyphosate tolerant technology (see citations 

in Figure 1.1).

In 2000, glyphosate came off patent and prices slowly began to fall as generic glyphosate 

producers increased production. Falling glyphosate prices provided further incentives to 

adopt glyphosate tolerant technology (see Figure 1.2 and Table 1.2). Supply issues from 

generic glyphosate producers in 2008 drove prices back up, but this price increase was

temporary (see Figure 1.2). 

By 2004, Marra et al., noted that glyphosate tolerant technology continued to be adopted 

for soybeans despite the fact that prices of herbicides used for conventional soybeans had 

fallen to the point where the cost of these herbicide bundles were competitive with 

glyphosate tolerant soybeans.

10

 Note that the adoption growth rate in soybeans slowed 

after 2004, but still increased. New studies have shown that profitability is not the only 

driver of adoption rates. Other factors such as compatibility with the use of other 

herbicides, ease of use, observable in-field results, and flexibility in application timing

can drive the adoption of a new technology, and have done so here.

11, 12 ,13, 14, 15, 16, 17 The 

results and convenience associated with glyphosate tolerant crops are discussed below in 

section 2.

Figure 1.2 U.S. glyphosate prices

Source: Proprietary data source, 2009.

2

Adoption of glyphosate tolerant corn has occurred more slowly than adoption of 

glyphosate tolerant soybeans. For corn there were already several effective pre- and post 

$0.00

$2.00

$4.00

$6.00

$8.00

$10.00

$12.00

$14.00

$16.00

Dollars Per Pound of Acid Equivalent
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emergent weed control herbicides in place that could be effectively used for 

preemergence weed control.18 In addition, glyphosate tolerant corn was not approved for 

import into the EU until late 2003, thereby limiting the export market for glyphosate 

tolerant grain. 

Table 1.2 Percent of all soybeans planted to herbicide tolerant varieties by state

Source: USDA's June "Acreage" Report, various issues, 2000-20091

2 Benefits of Glyphosate Tolerant Crops

As discussed below, the use of glyphosate tolerant crops has been shown to promote the 

use of conservation tillage practices. “Conservation tillage” refers to the use of 

herbicides to control weeds before, at, or after planting, rather than tilling the soil and 

“plowing up the weeds” to control them. By reducing soil erosion, conservation tillage 

preserves topsoil, soil structure, improved water infiltration and holding capacity as well 

as improved water quality by reducing soil, pesticide and fertilizer run-off. Additionally, 

greenhouse gas emissions are decreased by reducing tractor trips across fields, and 

allowing the soil to sequester carbon through increased soil organic matter.

2.1 Environmental Benefits

2.1.1 Enables conservation tillage with glyphosate tolerant crops

Many studies have noted a linkage between the rapid adoption of glyphosate tolerant 

crops and conservation tillage practices.4, 10, 19, 20, 21, 22 The literature varies somewhat in 

its conclusions on causality, but there is consensus that glyphosate tolerant crops enabled

greater adoption of conservation tillage including minimum and no-till practices. If 

herbicides are used to control weeds before, at, or after planting, the need for tillage 

before and after planting is eliminated. The National Academy of Sciences concludes in 

State 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

Percent of all soybeans planted

Arkansas 43 60 68 84 92 92 92 92 94 94

Illinois 44 64 71 77 81 81 87 88 87 90

Indiana 63 78 83 88 87 89 92 94 96 94

Iowa 59 73 75 84 89 91 91 94 95 94

Kansas 66 80 83 87 87 90 85 92 95 94

Michigan 50 59 72 73 75 76 81 87 84 83

Minnesota 46 63 71 79 82 83 88 92 91 92

Mississippi 48 63 80 89 93 96 96 96 97 94

Missouri 62 69 72 83 87 89 93 91 92 89

Nebraska 72 76 85 86 92 91 90 96 97 96

North Dakota 22 49 61 74 82 89 90 92 94 94

Ohio 48 64 73 74 76 77 82 87 89 83

South Dakota 68 80 89 91 95 95 93 97 97 98

Wisconsin 51 63 78 84 82 84 85 88 90 85

Other States 54 64 70 76 82 84 86 86 87 87

U.S. 54 68 75 81 85 87 89 91 92 91
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their 2010 report, "Given that agriculture is the largest source of surface water pollution, 

improvements in water quality resulting from the complementary nature of herbicideresistance technology and conservation tillage may represent the largest single 

environmental benefit of GE [Genetically Engineered] crops." 18

The American Soybean Association conducted a survey of famers in 2001 asking what 

factors had the greatest impact on their adoption of reduced tillage or no-till soybeans. 

Fifty four percent of the survey respondents indicated that the release of glyphosate 

tolerant soybeans had the greatest impact.23 The next largest factor, with 15 percent of 

the respondents, was improvements in reduced till or no-till planters. Another 

comparison that is a bit more striking was made by Dill, et al. in 2008.24 The percent of 

glyphosate tolerant soybeans planted via no-till was nearly 50 percent compared with 

conventional soybeans at 32 percent. Conventional tillage was used on about 32 percent 

of glyphosate tolerant soybeans, but nearly 50 percent of conventional soybeans.24 

Unfortunately the development of glyphosate resistant weeds and weed population shifts 

to hard-to-control weeds is jeopardizing the gains in conservation tillage. As noted 

below, in section 3.4, increased tillage is identified as a primary grower means to control 

glyphosate resistant weeds.5, 25, 26

2.1.2 Reduces soil erosion

When adoption of glyphosate tolerant soybeans and corn encourages parallel adoption of 

conservation and reduced tillage practices, improved soil and water conservation can be 

obtained. Conservation and reduced tillage can increase the availability of organic matter 

and minerals in the soil leading to enhanced soil structure and fertility. Soil erosion and 

water runoff are also reduced, sustaining the productive capacity of land and minimizing 

surface and groundwater contamination.20, 27 Due to improved soil moisture content and 

retention capacity, efficiencies in water use may also be achieved.28, 21, 29 

2.1.3 Reduces greenhouse gas emission

Increased no till cultivation enabled by glyphosate tolerant crop technology has two air 

quality impacts: reduction in fuel consumption and increased carbon sequestration within 

the soil.29, 20, 21 Reduction in fuel use through less tillage as well as less intensive tillage 

is well documented for conventional versus conservation tillage (see Section 2.2.2

below). In addition, by leaving the soil profile intact, a greater amount of organic carbon 

in the form of crop residue is sequestered in the soil. Sequestering more carbon in the 

soil leads to a reduction in green house gas (GHG) emissions. Brookes and Barfoot 

partitioned these GHG impacts from herbicide resistant soybeans and canola into carbon 

emission reductions from reduced fuel consumption and increased carbon sequestration.30 

Relative to conventional tillage, they increased carbon sequestration by a rate of 300 kg 

carbon/hectare-1for no-till and 100 kg carbon/hectare-1for reduced tillage. They describe 
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these rates as conservative relative to the range of 50 kg/hectare-1to 1,300 kg 

carbon/hectare-1suggested by the International Panel on Climate Change. Using these 

carbon sequestration rates, Brookes and Barfoot estimated that the fuel savings amounted 

to 1,117 million kg of carbon dioxide savings and additional carbon sequestration

amounted to 13,548 million kg of carbon dioxide savings in 2006. This is equivalent to 

removing roughly 6.5 million cars from the road.30

2.2 Economic Benefits

One of the primary reasons glyphosate tolerant crop technology has been so popular with 

growers is the strong economic incentive. The incentives are primarily driven by lower 

costs of production including lower costs for chemicals, fuel, labor, and management.

2.2.1 Reduces chemical costs

Studies indicate that chemical costs for growers of glyphosate tolerant crops are 

substantially lower in part because those growers have been able to control weeds 

through glyphosate alone without the assistance of other herbicides until recently.9 In 

1997, USDA found that soybean herbicide costs were reduced 11 percent by glyphosate 

tolerant crop technology in the primary growing area of the United States6. In addition, 

when glyphosate came off patent in 2000, its price declined by 40 percent (Figure 1.2). 

In 2003, Sankula and Blumenthal found that soybean herbicide costs were reduced 53 

percent by glyphosate tolerant crop technology. 31, 28 Slightly lower soybean herbicide 

cost reduction estimates of 46 percent were found by Sankula for 2005.28, 32 In summary, 

overall, the introduction of glyphosate tolerant soybean resulted in a reduction in weed 

control costs.

2.2.2 Reduces fuel costs

Energy costs are also reduced through glyphosate tolerant crop technology. As discussed 

above, the expansion of conservation tillage practices and glyphosate tolerant crop

technology have been found to complement each other. NAS states that glyphosate can 

be used to "supplement or replace tillage" in controlling most weeds, reducing fuel and 

labor inputs.18 In USDA's fuel simulator, fuel consumption is reduced by 44 percent in 

corn and 60 percent in soybeans by switching from conventional tillage to no-till methods 

(see Figure 2.1).33 In 2006, Mitchell et al. found that reduced tillage systems in 

California cotton reduced fuel use by 42 to 62 percent.34 Sanders found similar results,

with conservation tillage reducing fuel costs as much as 50 percent.

35

 Another source of 

fuel savings referenced in the literature is a reduction in herbicide applications.5, 25

Reduction in tillage and spraying also results in lower farm machinery expenses. Shortterm machinery repairs are lower and less usage extends the life of farm machinery,

thereby reducing the long run cost of equipment.18
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Figure 2.1 Corn and soybean fuel consumption by tillage type, Central Corn Belt

Source: USDA-NRCS, May 2010. 33

2.2.3 Reduces labor costs

Labor savings result in part from reduced tillage and also fewer herbicide applications. 

Sanders estimates a 40 percent reduction in labor costs through conversion to 

conservation tillage practices.35 Jasa reports that labor was reduced from 1.22 hours per 

acre to 0.49 hours per acre with a shift from moldboard plow tillage to no-till.36

2.2.4 Reduces management costs

Management costs (time and effort expended to control of weeds) are also reduced with 

glyphosate tolerant technology allowing growers to farm more land or increase their 

hours at an off-farm job. Recent studies have found a positive relationship between off 

farm income and the adoption of glyphosate tolerant soybeans.37, 38 These studies 

concluded that a 15.9 percent increase in off-farm household income is associated with a 

ten percent increase in the probability of adopting glyphosate tolerant soybeans. Other 

studies have found that adopting glyphosate tolerant soybeans reduces farm labor 

requirements by 23 percent.39

0.0

1.0

2.0

3.0

4.0

5.0

6.0

Conventional

Till

Mulch Till Ridge Till No-Till Conventional

Till

Mulch Till Ridge Till No-Till Gallons of Fuel Per Acre

Corn Soybeans

-26%

-33%

-44% -38%

-33%

-60%
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2.2.5 Global economic benefits

The reduction in costs of production at the farm level translates directly into an aggregate 

reduction in costs, enabling growers to obtain the same level of production at lower costs. 

In economics, this corresponds to a rightward shift in the supply curve which, assuming 

other factors remain constant, promotes a drop in the price of soybeans and an 

improvement in consumer welfare. These positive economic impacts extend to the 

grower through lower production costs, to the company supplying the technology through 

product sales, to other co-product sales such as seed (the carrier of the technology in this 

case), and to global consumers through lower commodity prices.28

Many studies have estimated the economic benefits of glyphosate tolerant crop

technology, focusing on one or more of the areas realizing the economic benefits. While 

studies looking at the global welfare for all sectors provide the most complete picture of 

economic benefits, not all studies are this broad. In any case, the literature documents 

economic benefits, particularly for growers and global consumers. Brooks and Barfoot 

focused on the farm income benefits of glyphosate tolerant technology. They reported 

global economic benefits to farm income from glyphosate tolerant soybeans over the 

1996-2004 period of $9.3 billion.29 Falck-Zepeda estimated the total increase in global 

welfare from glyphosate resistant soybeans for one year, 1997/98, at $1.06 billion.40 

Moschini et al. estimated the total global welfare from glyphosate tolerant soybeans for 

the year 2001 at $1.2 billion.41 In 2002, Qaim and Traxler estimated the global welfare 

effects of glyphosate tolerant soybeans for 2001 at $1.2 billion.42 In a study by Trigo and 

Cap of the Argentine soybean industry, accumulated savings in global consumer 

spending over the 1996-2005 from growers in Argentina adopting glyphosate tolerant 

soybeans was $26 billion.43 Finally, in 2008, Konduru et al. estimated a total global 

welfare increase for all glyphosate resistant soybean adoption, including losses from a 

shift away from the minor oilseeds, of $31.4 billion over the 1996 to 2006 period.28

2.3 Yield Enhancement

The opportunity for glyphosate tolerant crops to boost crop yields is driven by the ability 

of glyphosate to better control weeds. Empirical evidence of yield enhancement through 

use of glyphosate tolerant crop technology is somewhat conflicting. Many of the early 

studies show yield drag in soybeans, particularly in areas outside the primary soybean 

growing area. 42, 44, 45, 46, 47 In 2002, Marra, et al. suggested that yield drags in the early 

years of adoption disappeared over time as glyphosate tolerance was introduced into 

more elite soybean varieties.28, 48 Other studies have shown an increase in yields with 

glyphosate tolerant technology, particularly in the main growing region of the United 

States.2, 40, 49
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In 2010, Carpenter summarized the results from 49 peer reviewed studies that reported 

comparisons of yields for non-glyphosate tolerant and glyphosate tolerant crops

50. Of the 

14 studies reporting specific results for glyphosate tolerant soybeans in developed 

countries, none of the studies showed a yield decrease and the average increase in 

soybean yields was seven percent. Only three studies reported specific results for 

glyphosate tolerant soybean in developing countries, but again none of the studies 

showed a yield decrease and the average increase in soybean yields was 21 percent. 

While the sample size is too small to draw specific conclusions, these results could be 

representative of different weed pressures in developing versus developed countries. 

Growers in developed countries can more easily access alternative options for effective 

weed control compared to developing countries where effective weed control options 

may be more limited.50 Therefore, the potential for yield enhancement may be greater in 

environments with higher weed pressures.51 To the extent that existing weed control 

programs prior to glyphosate tolerant crop technology controlled weeds, the yield impact 

from adopting glyphosate tolerant crops may be smaller.

In Section 3 of this report, a detailed discussion of weeds that have developed resistance 

to glyphosate is presented. Weed resistance and shifts in weak populations suggest the 

importance of complementary systems which control hard-to-control weeds while 

allowing continued use of glyphosate in controlling the broad spectrum of weeds still 

susceptible. 

2.4 Results and Convenience

Throughout the literature, the simplicity and flexibility of glyphosate tolerant crops is 

mentioned repeatedly as one of the major benefits of this technology.20, 52 But what 

exactly does that mean? First, and foremost, is the manner in which glyphosate tolerant 

crop technology works. As a non-selective broad spectrum herbicide, glyphosate will 

control virtually all susceptible weed species with one or two appropriately applied post 

emergent applications to the glyphosate tolerant crop (i.e. applied after the crop has 

emerged). Contrast this simplicity with conventional herbicide alternatives that can 

involve hiring a crop consultant to prescribe a combination of herbicides appropriate to 

the crop with the right selectivity for the weed spectrum for each field on the farm. 

Second, simplicity also extends to the "over-the-top" application of glyphosate on 

glyphosate tolerant crops, allowing greater ground speed and much wider coverage in a 

single spraying pass in contrast to more directed spray applications for other herbicides.

11

Third, glyphosate tolerant crops offer considerable flexibility at planting time. Typically, 

growers in the U.S. Corn Belt will plant corn before soybeans due to its longer growing 

season and its yield sensitivity to weather conditions at the silking stage. However, 

weather delays can play havoc with the planting season and make the planting window 

very narrow for optimal yields. Glyphosate tolerant corn and soybeans allow growers a 
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longer window for weed control since they can return to the field and spray the crop at a 

later date rather than be limited to only applying weed control at planting or early post 

emergence as is the case with many other herbicides. In addition, glyphosate will control 

larger weeds (up to 10 cm are controllable in most circumstances), compared to other 

postemergent herbicides, further expanding the window for weed control.27 Glyphosate 

also has no residual soil herbicidal activity allowing maximum cropping flexibility.26 

Finally, flexibility also encompasses the enabling of conservation tillage practices. 

Glyphosate tolerant crops allow weed control without tillage. By reducing the amount of 

tillage, labor requirements fall, allowing growers more time to complete planting in a 

timely manner for optimal crop yields and/or expand their farming operation thereby 

reducing their fixed cost per bushel produced.26 Brookes and Barfoot concluded in their 

study that glyphosate tolerant soybeans have enabled an expansion in second crop 

soybeans in Argentina due to the time savings alone from reduced tillage. They estimate 

the net value over variable costs of the additional second crop soybeans at $699 million 

in 2006.30

Figure 2.2 Benefits of glyphosate tolerant crops 

Glyphosate

Tolerant

Crops

Complementary with

reduced tillage

• Reduces soil loss

• Lowers energy usage

• Improves carbon

sequestration

• Lowers greenhouse gas

emissions

Convenience

•Simplifies herbicide

application

• Accelerates speed of

application

• Saves management time

• Increases flexibility

• Enhances production

process simplicity

Cost reduction

• Lowers energy costs from

fewer tillage passes and

less intensive tillage

• Reduces herbicide cost

• Reduces labor costs

• Lowers machinery costs

Yield enhancement

• Improves yields on 

farms in developing

regions

• Potentially enhances

yields in developed

countries depending on

weed pressure
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3 Weed Management in Glyphosate Tolerant Corn and Soybeans

Proper weed control has always been a critical challenge for crop growers because weeds 

compete with crops for light, water and nutrients. Herbicides used in modern agricultural 

systems enable growers to manage most weeds across vast acreages. However, weed 

changes can occur in response to herbicide use as it can for other types of agricultural 

management decisions. Changes in weed populations begin when a subset of plants 

within a weed species, called a “biotype,” have a distinct genetic makeup that allows 

them to resist and survive a particular herbicide application. As a grower continues to 

use a particular herbicide without any other herbicide modes of action that are active 

against the resistant biotype, or doesn’t use any other weed control practices, the resistant 

biotype continues to survive and produce seed while susceptible biotype(s) of that weed 

are controlled. Subsequent populations of the resistant biotype will continue to increase 

until they are the dominant weed in the field.

As detailed in the previous sections, the introduction of glyphosate tolerance into crops 

through genetic engineering has revolutionized crop protection. Glyphosate is a broadspectrum herbicide with favorable environmental characteristics and effective broadspectrum weed control that has greatly improved crop protection efficiency. The 

widespread adoption of glyphosate tolerant crops, and subsequent glyphosate use, on a 

large portion of the available agronomic cropland has resulted in a strong selection 

pressure for weed biotypes that are not controlled by glyphosate; glyphosate resistant

weeds and hard-to-control weeds. After a little more than a decade of use, the utility of 

this technology is threatened by the occurrence of glyphosate resistant and hard-tocontrol biotypes of certain weed species.

Glyphosate resistant weed species such as marestail, ragweed, waterhemp and Palmer 

amaranth and hard-to-control species such as lambsquarters and morning glory species 

are quickly spreading through corn and soybean producing states (Figure 3.3). The 

potential magnitude of the problem affects an estimated 15 to 20 million acres of corn 

and soybeans and presents important agronomic and economic challenges to growers and 

the agricultural industry (Table 3.1). University weed scientists from across the country 

have warned of the impact of glyphosate resistant weeds on the profitability and 

sustainability of current cropping systems and believe that a higher level of stewardship 

is required to sustain the benefits of glyphosate and glyphosate tolerant crops into the 

future.53 Management of the spread of hard-to-control and herbicide-resistant weeds will 

likely guide the direction of crop production in the future.54 Growers clearly need more 

effective and diverse tools to manage glyphosate resistant and hard-to-control weeds in 

order to sustain the long-term viability of the glyphosate tolerant cropping system and 

preserve the benefits it provides to growers, the agricultural industry, and society.
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3.1 Herbicide resistance

The evolution of herbicide-resistant weeds is not unique to glyphosate. Currently, 195 

species (115 dicots and 80 monocots) have evolved resistance to at least one of 19 

herbicide modes of action (the means by which a herbicide achieves the intended effect 

on the plant) in at least 347 herbicide-resistant weed biotypes distributed over 340,000 

fields (Figure 3.1).55

Figure 3.1 Global reports of herbicide resistant weeds

As discussed above in Section 1.2, corn and soybean production in the United States was 

drastically altered with the introduction of glyphosate tolerant technology in 1996 and 

1998. By 2009, producers grew glyphosate tolerant varieties and used glyphosate for 

weed control on approximately 95 percent and 82 percent of the soybean and corn acres, 

respectively.56 The growers on these acres were generally not using other weed control 

practices, and the situation outlined above occurred – weed biotypes that were not killed 

by glyphosate survived and reproduced.57 In response to the selection pressure (i.e. a 

reduction in the reproductive success of the glyphosate susceptible weed biotypes as a 

result of glyphosate treatment) imposed by these practices, the composition and structure 

of weed communities in agricultural fields have been altered.57 A total of eleven weed 

species have developed resistance to glyphosate in the United States. Nine of these 
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species have evolved resistance to glyphosate in GT crops since their introduction 13 

years ago.55 The nearly exclusive reliance on glyphosate for weed control on glyphosate 

tolerant crop varieties has caused substantial changes in weed communities. Figure 3.2 

shows this relationship of the adoption of glyphosate tolerant corn and soybeans to the 

development of glyphosate resistant weeds.

Figure 3.2 Adoption of glyphosate tolerant crops and development of glyphosate 

resistant weeds in the United States

Sources: Third party proprietary data – Iain Heap http://www.weedscience.org.

The first report in the United States of glyphosate resistance in weeds associated with a 

glyphosate tolerant crop involved horseweed in Delaware.58 Growers found it difficult to 

control this weed in no-till glyphosate tolerant soybeans once resistance evolved since 

tillage was not used to “plow under” any resistant biotypes. Since the initial report in 

2000, glyphosate resistant populations of horseweed have been documented in 16 states 

throughout the Mid-Atlantic, Mid-South, Mississippi Delta, and Midwest states.55 Since 

the discovery of glyphosate resistant horseweed in 2000, eight other weed species have 

evolved resistance to glyphosate in glyphosate tolerant crops in the United States 

including Palmer amaranth, waterhemp, Johnsongrass, common ragweed, giant ragweed, 

kochia, Italian ryegrass and Johnsongrass (Table 3.1).

110%

19961997199819992000200120022003

200420052006200720082009

11

# of Confirmed Gly-Res Weeds in U.S.

GT Soybean GT Cotton GT Corn

% of Acres with GT Crop
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Table 3.1 Weeds that evolved resistance to glyphosate in glyphosate tolerant crops in the 

United States

Species Crop State Acreage*

Amaranthus palmeri 

(Palmer amaranth)

Corn, cotton, soybean Georgia, North Carolina, 

Arkansas, Tennessee, 

Mississippi

200,000–2,000,000

Amaranthus tuberculatus 

(waterhemp)

Corn, soybean Iowa, Missouri, Illinois, 

Kansas, Minnesota

1,200–11,000

Ambrosia artemisiifolia 

(common ragweed)

Soybean Arkansas, Missouri, 

Kansas

<150

Ambrosia trifida (giant 

ragweed)

Cotton, soybean Ohio, Arkansas, Indiana, 

Kansas,

Minnesota, Tennessee

2,000–12,000

Erigeron canadensis

(horseweed)

Corn, cotton, soybean Arkansas, California, 

Delaware, Illinois, 

Indiana, Kansas, 

Kentucky, Maryland, 

Michigan, Mississippi, 

Missouri, New Jersey, 

North Carolina, Ohio, 

Pennsylvania, Tennessee

> 2,000,000

Kochia scoparia (kochia) Corn, soybean Kansas 51-100

Lolium multiflorum 

(Italian ryegrass)

Cotton, soybean Mississippi 1000–10,000

Sorghum halepense 

(Johnsongrass)

Soybean Arkansas Unknown

* Minimum and maximum acreages are based on expert judgments provided for each state. The estimates 

were summed and rounded to provide an assessment of the minimum and maximum acreages in the United 

States. These values indicate orders of magnitudes but do not provide precise information on abundance of 

resistant weeds and likely underestimate actual acreage because the estimates were made when the 

resistance was first identified.

Source: Data from Heap, 2010.

3.2 Other shifts in weed communities (hard-to-control species)

The makeup of weed communities in agronomic fields is influenced by many factors in 

addition to herbicide use including tillage, crop rotation, soil characteristics, 

environmental factors, and management practices. Weeds that naturally tolerate 

glyphosate tolerant crop weed management practices are referred to as “hard-to-control” 
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weeds. As described above, the adoption of glyphosate tolerant cropping systems has 

contributed to large increases in the percentage of growers using no-till and reduced-till 

systems.59 In response to these tillage practice changes, winter annual and perennial 

weed species have become more prevalent after the widespread adoption of glyphosate 

tolerant crops because they are not “plowed under” and can survive to reproduce and 

spread. For example, horseweed, which behaves primarily as a winter annual weed, was 

rarely an economic problem in conventionally tilled fields, but has become a problem in 

no-till and reduced till fields. Weeds, like waterhemp, that continue to germinate after 

the last glyphosate application, escape control, and have an advantage in glyphosate 

tolerant crops.60 Some weeds are naturally more tolerant of glyphosate, such as 

lambsquarters, wild buckwheat and morning glory species and have become more 

prevalent (Table 3.2). Table 3.2 lists weed species that have been found to become more 

abundant after the widespread adoption of glyphosate tolerant crops excluding resistant 

biotypes discussed above in Section 3.1.

3.3 Potential for future spread of glyphosate resistant and hard-to-control weeds in 

glyphosate tolerant crops

Glyphosate resistant and hard-to-control weeds are rapidly increasing in agricultural 

fields both in the number of species with resistant biotypes and the acreage infested 

(Figure 3.3). Tables 3.3-3.4 and Figure 3.3 present future assumptions for glyphosate 

resistant weed development in corn and soybeans in the United States. Several common 

annual grass and broadleaf weeds are expected to develop resistance to glyphosate during 

the next five years including lambsquarters, velvetleaf, barnyardgrass and foxtail. Dow

AgroSciences projects that approximately 30 million acres (20 percent of the 160 million 

total corn and soybean acres) will become infested with glyphosate resistant weeds by 

2020 (Table 3.3 and Figure 3.4), while Syngenta projects that glyphosate resistant weeds 

will infest 38 million acres by 2013 (Table 3.4 and Figure 3.4). As a result, glyphosate 

resistant and hard-to-control weeds are projected to impact management decisions on 

nearly half of the corn and soybean acres in the United States within ten years.
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2001

✔ Marestail

2005

✔ Marestail

✔ Common Ragweed

✔ Giant Ragweed

✔ Palmer Amaranth

✔ Common Waterhemp

✔ Italian Ryegrass

2009

✔ Johnson Grass

✔ Kochia

✔ Marestail

✔ Common Ragweed

✔ Giant Ragweed

✔ Palmer Amaranth

✔ Common Waterhemp

✔ Italian Ryegrass

Figure 3.3 Glyphosate Resistant Weeds

Change in Prevalence: 2001, 2005, 2009

Source: http://www.weedscience.org
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Table 3.2 Weeds reported to have increased in abundance in glyphosate tolerant 

crops

Species Crop

Acalypha spp. (copperleaf) Soybean

Amaranthus tuberculatus (waterhemp) Soybean

Amaranthus palmeri (Palmer amaranth) Cotton

Annual grasses Cotton

Chenopodium album (common 

lambsquarters)

Soybean Iowa

Commelina communis (Asiatic dayflower) Cotton, soybean Midwest, Midsouth, Southeast

Commelina benghalensis (tropical 

spiderwort)

Cotton Southeast, Georgia

Cyperus spp. (nutsedge) Cotton

Equisetum arvense (field horsetail) Herbicide-resistant crops

Oenothera biennis (evening primrose) Herbicide-resistant crops Iowa

Oenothera laciniata (cutleaf evening 

primrose)

Soybean

Pastinaca sativa (wild parsnip) Herbicide-resistant crops Iowa

Phytolacca americana (pokeweed) Herbicide-resistant crops

Ipomoea spp. (annual morning glory) Cotton

Source: Ervin, D. E. et.al. 2010. Impact of Genetically Engineered Crops on Farm Sustainability in the 

United States. Committee on the Impact of Biotechnology on Farm-Level Economics and Sustainability; 

National Research Council. ISBN: 0-309-14709-3, 240 pages, 6 x 9. 

http://www.nap.edu/catalog/12804.html. Accessed: April 28, 2010.
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Table 3.3 Future assumptions for glyphosate resistant weeds in corn and soybeans 

in the United States*

Corn and Soybean Acres Today (2010) By 2015 By 2020

Glyphosate resistant weed 

species present or predicted

Marestail 

Common ragweed

Giant ragweed

Palmer amaranth

Waterhemp 

Kochia 

Rigid ryegrass

Johnsongrass 

All 2010 weeds, 

plus

Lambsquarters

Velvetleaf

Barnyardgrass

Giant foxtail

Goosegrass

All weeds listed 

in 2010 and 2015

Estimated acres infested with 

glyphosate resistant weeds 7.5 M acres 15 M acres 30 M acres

% infested with glyphosate 

resistant weeds 5% 10% 20%

Estimated % of acres on which 

weed management decisions 

are impacted by glyphosate 

resistant weeds

10% 20% 40%

* Future assumptions for glyphosate resistant weeds in U.S. corn and soybeans are based on a 75-89% 

probably.

Source: Dow AgroSciences LLC.
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Table 3.4 Future assumptions for glyphosate resistant weeds in corn and soybeans 

in the United States, Syngenta Corporation

Category Species

Key weeds developing resistance in corn and 

soybean fields over a broad area of the corn 

belt

Waterhemp

Pigweed species

Horseweed

Probable resistant weeds by 2010-2015 Foxtail

Barnyardgrass

Johnsongrass

Source: Syngenta Resistance FighterTM Message Board. http://www.resistancefighter.com/about/weeddetail.aspx?Id=91163; 

Figure 3.4 Projected corn and soybean acres infested with glyphosate resistant 

broadleaf and grass weeds in the United States (excluding volunteer glyphosate 

resistant corn).

Sources: 

 Foresman, C. 2009. Syngenta Resistance FighterTM Message Board. http://blog.syngentaus.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
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3.4 Growers’ response to glyphosate resistant and hard-to-control weeds

Glyphosate resistance and other weed shifts can reduce the effectiveness and economic 

benefits of glyphosate tolerant crop systems. However, growers are reluctant to stop 

using glyphosate tolerant crops and glyphosate when faced with hard-to-control weed 

species. Despite reduced weed control, growers have constructed their farming 

enterprises around glyphosate and glyphosate tolerant crops, and they prefer the 

convenience, broad spectrum control and economic benefits of using glyphosate.57 So 

they prefer to increase glyphosate application rates, increase the number of glyphosate 

applications, use other herbicides in addition to glyphosate, and/or increase tillage to 

control problem weeds. Figures 3.5 and 3.6 show how glyphosate rates and the number 

of glyphosate applications applied on corn and soybeans have steadily increased with the 

widespread adoption of glyphosate tolerant crop systems and evolution of glyphosate 

resistant and hard-to-control weeds. Figure 3.7 shows the impact of increasing 

glyphosate rates and application frequency, and the increase in glyphosate tolerant corn

acres on total glyphosate use on corn and soybeans. (Please note that the glyphosate 

tolerant soybean acreage was flat from 2006-2009, so the increase in pounds of 

glyphosate used during this time period resulted from higher glyphosate application rates 

and frequency. Corn acres, however, grew during this time period and account for much 

of the glyphosate increase.)

Figure 3.5 Average postemergence glyphosate use rates on corn and soybeans in the 

United States.

Source: Third party proprietary data Lb. ai/Acre

Corn Soybeans

0.9
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Figure 3.6 Average number of glyphosate applications on corn and soybeans in the 

United States (includes burndown uses)

Source: Third party proprietary data

Figure 3.7 Total pounds of glyphosate applied on corn and soybeans in the United 

States (includes burndown uses)

Source: Third party proprietary data No. of Glyphosate Applications 

Corn Soybeans Corn Soybeans

1.75 Lb Glyphosate Applied

Corn Soybeans

120,000,000
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In addition to higher rates and application frequency of glyphosate, growers have 

increased their use of non-glyphosate herbicides in glyphosate tolerant crop systems in 

order to introduce additional herbicide modes of action for control glyphosate resistant

and hard-to-control weeds. The use of preemergence residual herbicides nearly doubled, 

increasing from approximately 40 percent to 75 percent of the glyphosate tolerant corn

acreage and from 20 percent to 34 percent of the glyphosate tolerant soybean acreage 

from 2000 to 2009 (Figures 3.8 and 3.9). During this same timeframe, the use of 

postemergent non-glyphosate herbicides on glyphosate tolerant corn more than doubled 

from approximately 15 percent of the glyphosate tolerant corn acreage in 2000 to 39

percent in 2009 (Figure 3.10). Postemergent use of non-glyphosate herbicides on 

soybeans followed a slightly different pattern (Figure 3.11). Use of these herbicides on 

glyphosate tolerant soybeans was approximately eight percent of the glyphosate tolerant 

soybean acres in 2000 and 2001, then dipped to five percent in 2004-2006, and increased 

to 11 percent in 2009.

Unfortunately, the use of non-glyphosate herbicides does not always address weed 

resistance issues. Growers do not always use broad-spectrum herbicides to supplement 

glyphosate, so even when utilizing these alternative modes of action, glyphosate still 

provides the control of certain weeds while the supplemental herbicide has no effect on 

those weeds.61 In addition, growers often apply reduced rates of non-glyphosate 

herbicides, resulting in a reduced spectrum of control and frequent weed escapes.62,63 

Glyphosate still provides control of certain weeds when used in combination with 

reduced rates of non-glyphosate herbicides. 
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Figure 3.8 Preemergence non-glyphosate herbicide usage on glyphosate tolerant corn

Source: Third party proprietary data

Figure 3.9 Preemergence non-glyphosate herbicide usage on glyphosate tolerant soybeans

Source: Third party proprietary data

80,000,000

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

40%

RR Soybean Acres Non Glyphosate Herbicide Acres % of RR Soybeans with Non Gly Herbicide

80,000,000

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

80%

RR Corn Acres Non Glyphosate Herbicide Acres % of RR Corn with Non Gly Herbicide
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Figure 3.10 Post-emergence non-glyphosate herbicide usage on glyphosate tolerant corn

Source: Third party proprietary data

Source: Third party proprietary data

80,000,000

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

12%

RR Soybean Acres Non Glyphosate Herbicide Acres % of RR Soybeans with Non Gly Herbicide

80,000,000

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

45%

RR Corn Acres Non Glyphosate Herbicide Acres % of RR Corn with Non Gly Herbicide

Figure 3.11 Post-emergence non-glyphosate herbicide usage on glyphosate tolerant soybeans (excludes products 

typically used to control volunteer corn)
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Several peer-reviewed journal articles have been published on grower response to 

glyphosate resistant and hard-to-control weeds in glyphosate resistant crops. The 

following literature review is summarized from the National Research Council report 

entitled “Impact of Genetically Engineered Crops on Farm Sustainability in the United 

States.18

 “Soybean growers in Delaware continued planting glyphosate-resistant soybean 

even in the presence of widespread glyphosate resistance in horseweed. Most 

producers addressed the problem by applying a herbicide with a different mode of 

action, increasing the frequency of glyphosate applications, or using tillage before 

planting. Some 76 percent of growers estimated that resistance in horseweed 

increased their management costs by more than $2.02/acre, and 28 percent 

reported cost increases of over $8.09/acre.” 

 “A survey of 400 corn, soybean, and cotton producers in 17 states found that most 

would not limit the use of glyphosate-resistant crops when facing problematic 

glyphosate-resistant weeds. Instead, producers planned to increase the rotation of 

herbicides, the use of tank-mixes, or the amount of tillage. They expected that 

additional measures for the control of glyphosate-resistant weeds would cost 

$13.90–16.30/acre.”

 “In an economic analysis of weed-management costs with a hypothetical 

reduction of control with glyphosate in three regions of the United States, the 

projected cost of new resistance-management practices for horseweed was 

$12.33/acre in a cotton–soybean–corn rotation in western Tennessee. Additional 

costs were due to a shift from no-till to conventional tillage for cotton and the 

need for new preplant herbicides for soybean.”

 “The projected cost of new herbicide resistance-management practices for 

waterhemp was $17.91/acre in a corn–soybean rotation in southern Illinois; this 

cost resulted from use of different preemergence and postemergence herbicides 

for soybean.”

 “For cotton grown in Georgia, the extra cost of controlling shifts in tropical 

spiderwort (Commelina benghalensis), a weed that is naturally tolerant to 

glyphosate, was predicted to be $14.91/acre; an additional herbicide application 

after cotton emergence explained this cost.”

The authors of the National Research Council report concluded from these studies that 

the evolution of glyphosate resistance and weed shifts could lead to two important 

changes in practices: increased use of herbicides generally and reductions in 

conservation tillage. The preceding literature review indicates that these changes will 

increase weed-management costs, reduce growers’ profits, and produce environmental 
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consequences. If widely adopted by growers, increased use of herbicides and tillage will 

negate the environmental benefits achieved through glyphosate tolerant crop systems. 

3.5 Weed management strategies to sustain glyphosate tolerant cropping systems in 

corn and soybeans

The key to controlling existing resistant weeds and slowing the development of new 

resistant weeds is to reduce and diversify selection pressure on the weed population while 

still maintaining economic levels of control.64 This requires a planned and integrated 

weed management approach combining: 

 Rotation of crops -- to allow a more varied weed control program 

 Rotation of cultural practices -- to reduce reliance on herbicides 

 Rotation of sequences and mixtures of herbicidal modes of action and chemistry -

- to reduce the pressure on a specific herbicide group. 

Diversification of weed-management strategies can be accomplished by integrating 

several weed-control tactics including the following:65

 Scout fields before and after herbicide application. 

 Start with a clean field, using either a burn-down herbicide application or tillage. 

 Control weeds early when they are relatively small. 

 Rotate herbicides that have different modes of action.

 Use residual herbicides that have different modes of action.

 Use tank-mixes of herbicides that have different modes of action.

 Incorporate other herbicides and cultural practices as part of glyphosate tolerant 

cropping systems where appropriate. 

 Use the right herbicide product at the right rate and the right time. 

 Control weed escapes and prevent weeds from setting seeds.

 Clean equipment before moving from field to field to minimize spread of weed 

seed. 

 Use new commercial seed as free from weed seed as possible. 

 Report any incidence of repeated non-performance on a particular weed to the 

local crop protection chemical company representative, retailer, or county 

extension agent.

The Herbicide Resistance Action Committee (HRAC, www.hracglobal.com) prepared the 

tool presented in Table 3.5 to help growers assess the value of weed resistance 

management practices and create an effective integrated weed management program. 

HRAC recommends that the number of applications of a single mode of action be limited 

in a single growing season. Where possible, HRAC recommends use of herbicide 

mixtures or sequential application of herbicides of different modes of action that are 

active on the same target weeds. In cases of confirmed herbicide resistance, HRAC 

advises farmers to avoid using the herbicide to which resistance has been confirmed 

unless used in conjunction with herbicides with a different mode of action active on the 

resistant weed population. 
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Resistance management through use of herbicide mixtures and rotation of herbicides is 

most effective if the partner herbicides are highly effective against the same weeds. A 

partner herbicide which is only marginally effective at controlling a weed or is used at a 

reduced application rate (to reduce crop damage), is not expected to effectively delay 

resistance.

62

Table 3.5 Assessment of resistance risk by evaluation of the cropping system

Management Option

Risk of Resistance

Low Moderate High

Herbicide mix or rotation in 

cropping system >2 modes of action 2 modes of action 1 mode of action

Weed control in cropping 

system

Cultural, mechanical 

and chemical

Cultural* and 

chemical Chemical only

Use of same MOA per 

season

Once More than once Many times

Cropping system Full rotation Limited rotation No rotation

Resistance status to MOA Unknown Limited Common

Weed infestation Low Moderate High

Control in last 3 years Good Declining Poor

* Cultural control can be by using cultivation, stubble burning, competitive crops, stale seedbeds, etc. See 

HRAC guidelines for more details. 

Source: Herbicide Resistant Action Committee. http://www.hracglobal.com

3.6 New tools for weed resistance management 

Without changes in production practices, increased weed resistance to glyphosate will 

likely increase weed-management expenses for growers. Given the rapid increase in, and 

expansion of, glyphosate resistant weeds in glyphosate tolerant crops, herbicide-
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resistance management needs national attention and requires the development and use of 

new, more effective weed-management strategies and tactics. New herbicide tools are 

critical to management of weeds with resistance to multiple modes of action.

Herbicide tolerant DAS-40278-9 corn allows the use of a new herbicide mode of action 

on corn, the aryloxyphenoxyproprionates class of grass herbicides (e.g. quizalofop) and 

confers robust tolerance to 2,4-D. This technology enables the use of a new mode of 

action on corn, for control of grasses, and efficacious application rates and flexible 

application timing for 2,4-D. 

Most university recommendations for control of glyphosate resistant and hard-to-control 

broadleaf weeds include 2,4-D as a control option for preplant burndown and 

postemergence applications in cornB. However, corn hybrids show differing levels of 

tolerance to 2,4-D so it has not been widely adopted and use rate restrictions to prevent 

phytotoxicity limit the spectrum of activity on weeds.66 2,4-D’s wide spectrum of 

broadleaf weed control complements glyphosate because it controls most glyphosate 

resistant and hard-to-control broadleaf weed species (Table 4.1 and Section 4.4). 2,4-D 

will control broadleaf weeds that are resistant to other modes of action such as ALSenzyme inhibitor and PPO inhibitor herbicides, including weeds with multiple resistance. 

Weed researchers are hopeful that new technologies, such as DAS-40278-9, will become 

useful tools to help manage glyphosate resistant and hard-to-control weeds in order to 

sustain the long-term viability of the glyphosate tolerant cropping system and preserve 

the benefits it provides to growers, the agricultural industry, and society.

4 Long-term Weed Resistance Management through Use of Herbicide Tolerant 

DAS-40278-9 

4.1 DAS-40278-9 corn enables use of alternative modes of action to glyphosate

DAS-40278-9 corn plants have been genetically engineered to express the 

aryloxyalkanoate dioxygenase (AAD-1) protein. The AAD-1 protein is an enzyme with 

an alpha ketoglutarate-dependent dioxygenase activity which results in metabolic 

inactivation of herbicides in the aryloxyalkanoate family. DAS-40278-9 corn enables 

tolerance to 2,4-dichlorophenoxyacetic acid (2,4-D)Cand to aryloxyphenoxypropionate 

(AOPP) herbicides (“fop” herbicides). 

 

B

For example: http://www.btny.purdue.edu/Pubs/ws/ws-16/

C

Dow AgroSciences is seeking EPA registration of a new 2,4-dichlorophenoxyacetic acid (2,4-D) product to 

be utilized with DAS-40278-9 corn. This proprietary choline salt of 2,4-D has ultra low volatility, improved 

stability at low temperatures and improved, lower odor. In addition, Dow AgroSciences is developing 

technology to significantly reduce the potential for off-target movement via spray droplet drift.
Supplemental Information for USDA Petition for Nonregulated Status of DAS-40278-9 Corn Page 37 of 50

Dow AgroSciences LLC

2,4-D and fop herbicides represent two distinct modes of action that are different from 

glyphosate which acts through a single mode of action. 2,4-D is a broadleaf herbicide 

that acts as a synthetic auxin causing uncontrolled growth and plant death. 2,4-D is 

classified by HRAC as a Group O herbicide (a synthetic auxin, acts like indole acetic 

acid) and Group 4 in the Weed Science Society of America (WSSA) mode of action 

classification scheme (a synthetic auxin, speicifc site(s) unknown). Each Group 

designation reflects a specific mode of action or how it affects the sensitive species.67 

The “fops” are grass herbicides that act by inhibiting acetyl coenzyme A carboxylase 

involved in lipid and fatty acid biosynthesis. The fops are classified by HRAC as Group 

A herbicides (Group 1 in the WSSA mode of action classification scheme). Glyphosate 

is a non-selective herbicide that acts by inhibition of 5-enolpyruvylshikimate-3-phosphate 

synthase (EPSPS), a key enzyme in the shikimate biosynthetic pathway. Glyphosate is 

classified by HRAC as a Group G herbicide (Group 9 in the WSSA scheme). 

4.2 Management of glyphosate resistant and hard-to-control weeds using herbicide 

tolerant DAS-40278-9 corn

From commercial launch, DAS-40278-9 will be stacked (the process of combining traits 

through traditional breeding) with glyphosate tolerance so that farmers will be able to use 

2,4-D and glyphosate together, thus simultaneously applying two different but 

complementary modes of action for both broadleaf and grassy weed control. Herbicide 

tolerant DAS-40278-9 corn enables weed resistance management practices that today are 

not possible. In corn varieties stacked with both DAS-40278-9 and glyphosate tolerance, 

the herbicide 2,4-D is an ideal complement to glyphosate to provide an exceptional pre 

and postemergent weed management program that is not available today and is readily 

adaptable to use with foundation herbicide programs. It has a similarly broad spectrum 

activity for control of broadleaf weeds, low mammalian toxicity, short soil residual 

activity, and a favorable environmental profile. Importantly, in applications to corn with 

tolerance to both 2,4-D and glyphosate (DAS-40278-9 corn stacked with a glyphosate

tolerance trait through traditional breeding), 2,4-D can be tank mixed with glyphosate or 

provided as a premix that will be cost effective to use. 2,4-D controls several key 

broadleaf weed species that are resistant to, or difficult to control with, glyphosate and 

ALS herbicides (Table 4.1). Mixtures of 2,4-D with glyphosate provide control of

glyphosate resistant biotypes and hard to control weeds that is superior to glyphosate 

alone.

Applications of 2,4-D to DAS-40278-9 corn therefore can play an important role in 

managing glyphosate resistant weed biotypes. It provides a new opportunity to preserve 

the economic, environmental, and convenience benefits of herbicide tolerant technology

 
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Dow AgroSciences LLC

even in the presence of glyphosate resistance. By growing crops that are tolerant to 2,4-

D, farmers will be able to control weeds that otherwise would become an increasing 

problem. It will enable farmers to avoid returning to environmentally damaging weed 

management practices such as tillage.

Table 4.1 Glyphosate resistant, ALS resistant weeds, and hard-to-control weeds 

that are controlled by 2,4-D

Weed Species

Glyphosate Resistance /

Hard-to-Control

Resistant to ALS 

Herbicides

Controlled by 

2,4-D

Common Lambsquarters Hard-to-control (2004)  (2001) 

Common Ragweed Confirmed Resistant (2004)  (1998) 

Eastern Black Nightshade Hard-to-control (2004)  (1999) 

Giant Ragweed Confirmed Resistant (2004)  (1998) 

Marestail (horseweed) Confirmed Resistant (2000)  (2000) 

Palmer Amaranth* Confirmed Resistant (2005)  (1991) 

Waterhemp Confirmed Resistant (2005)  (1993) 

Prickly Sida Hard-to-control (2004)  (1993) 

* Requires an integrated weed management plan, including additional weed control technology, for 

acceptable control.

While DAS-40278-9 corn will enable farmers to better manage glyphosate resistant

weeds through use of 2,4-D and quizalofop herbicides, they will also serve to reduce the 

selection pressure for resistance to glyphosate and prevent or delay the onset of new cases 

of resistance. Farmers will be able to apply mixtures of herbicides with two or more 

distinct modes of action. Such mixtures will prevent or severely limit the survival and 

reproduction of susceptible weeds which are developing resistance to one of the 

herbicidal modes of action because these weeds will be susceptible to the other 

herbicide(s) in the mixture.

68

 

For mixtures to be most effective at delaying resistance, each component alone should be 

highly efficacious on that weed species.69 Both 2,4-D and glyphosate individually 
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provide very high levels of control of important susceptible weed species when applied 

alone, and show the expected additivity when applied together. This means that when 

used together, any weed plants that may be developing resistance can be eliminated from 

the population, curtailing the increase and spread of the resistance. 

As an alternative to mixtures of herbicides, temporally separated spray applications to 

provide a rotation among modes of action within a growing season can be effective as 

part of a pre-emptive resistance management strategy.68 As with mixtures, a rotation 

approach to herbicide management is expected to prevent or delay the emergence of new 

weed management challenges due to resistance. Through these practices, the projected 

trajectory of new glyphosate resistant and hard-to-control weed issues, such as new 

resistant biotypes or expanded range of resistant and hard-to-control weed populations, 

can be slowed through the use of 2,4-D with herbicide tolerant DAS-40278-9 corn.

4.3 Proposed Use Pattern and Compatibility with Glyphosate Cropping System

To encourage a system that incorporates multiple modes of action, Dow AgroSciences 

has designed the technology to be compatible with the current glyphosate cropping 

system. 

DAS-40278-9 corn will provide rate and timing flexibility to growers to optimize their 

weed control programs. In contrast to the current use pattern for 2,4-D on corn which 

places rate and equipment restriction on the post emergent use in corn, there will be 

neither crop injury risk nor distinct spray timing and application rate restrictions. DAS40278-9 corn enables a continuous over-the-top application window from pre-planting 

through the postemergence stage of V8 (vegetative, 8 leaf stage) or 48” tall corn. This 

application window provides optimal flexibility for growers to manage their weed control 

program around cultural operations (including other crops) or climatic conditions. This 

window represents the critical weed control period when weed competition has the 

greatest detrimental effect on corn growth. Thus, the use of DAS-40278-9 corn allows 

the grower to apply herbicide when weeds are the most sensitive and corn is the most 

vulnerable to weed competition and thus better control hard-to-kill weeds. Additionally, 

this new application timing complements the glyphosate application timings in 

glyphosate resistant corn. When stacked (combining traits through conventional 

breeding) with glyphosate tolerance, the combination of 2,4-D and glyphosate provides 

an exceptional weed control system with maximum flexibility and efficiency for the 

grower. Similar to use on conventional corn, a maximum seasonal application rate for 

2,4-D will be 3.0 lbs ae/ac (acid equivalents/acre). While quizalofop is intended to be 

used as a selection agent to control corn plants without the DAS-40278-9 trait, in hybrid 

seed production, grass herbicide concepts can be developed to utilize quizalofop for 

control of grassy weeds in DAS-40278-9 corn. This will be the first use of this family of 

chemistry for grass weed control in corn. Quizalofop applications would be made up to 
Supplemental Information for USDA Petition for Nonregulated Status of DAS-40278-9 Corn Page 40 of 50

Dow AgroSciences LLC

the V6 (vegetative, 6 leaf) growth stage in corn. Figure 4.1 pictorially details the use 

pattern for 2,4-D and quizalofop on DAS-40278-9 corn and its compatibility with 

glyphosate applications.

* All 2,4-D application rates are lbs ae/ac, Pre = preemergence, Post = postemergence

The compatibility of the windows for application of all corn herbicides allows growers to 

easily incorporate DAS-40278-9 corn into their cropping system and increases the ease of 

delivering multiple modes of action to control weeds and mitigate the development of 

weed resistance.

4.4 Proactive resistance management for 2,4-D through integration with glyphosate

Herbicide tolerant DAS-40278-9 corn provides a new tool for managing and delaying 

glyphosate resistance, managing hard-to-control weeds, and preserving the benefits of the 

herbicide tolerant technologies. However sustainable success with DAS-40278-9 corn 

will require long-term management of resistance to 2,4-D and quizalofop as well as to 

glyphosate. A thorough discussion of weed resistance, how it develops, and its 

management can be found at the Herbicide Resistance Action Committee (HRAC) 

website.68 

2,4-D has been used since 1945 with relatively few weed resistance issues. Globally, 16 

weed species have documented reports of 2,4-D resistant biotypes, with only three in the 

V6

Figure 4.1 2,4-D, quizalofop, and glyphosate applications schedules for DAS40278-9 Corn*

Pre 1 lb/A Post 0.5-1 lb/A

 (up to 2 applications)

min of 12 days apart)

V8 

or 

 Glyphosate 48”

Pre-emergence

 Glyphosate

Post-emergence

 Glyphosate

 Pre-Harvest 

 Quiz post up to 

0.082 lb/A
Supplemental Information for USDA Petition for Nonregulated Status of DAS-40278-9 Corn Page 41 of 50

Dow AgroSciences LLC

continental United States (wild carrot, field bindweed, prickly lettuce).70 None of these 

are of substantial economic importance and none has shown a large degree of spread 

from their point of origin. The rarity of resistance to 2,4-D or other auxinic herbicides 

has been attributed to:71, 72, 73, 74,75

 multiple sites of action for these auxin herbicides in the plant,

 redundancy in receptors and other components of the auxin signal response,

 frequent use in mixtures with other herbicides,

 a fitness penalty associated with auxin resistance mechanisms in weeds, and

 quantitative inheritance of the trait

 short soil half-life (residual)

The fop (aryloxyphenoxypropionate) herbicides and other ACC-ase inhibitor herbicides 

have been used widely to control grass weed species since their introduction in the 1970’s 

and 1980’s. Today there are 15 weed species in the United States with documented 

resistance to one or more ACC-ase inhibitor herbicides.70 In the United States, there are 

no known instances of multiple-resistance to both glyphosate and ACC-ase inhibitors.70

The same principles of weed resistance management discussed above for glyphosate 

apply directly to 2,4-D and the fop herbicides. Unlike past experience with glyphosate, 

farmers will be encouraged to use multiple herbicide modes of action with DAS-40278-9 

corn to control their weed problems. From commercial launch, DAS-40278-9 will be 

stacked with glyphosate resistant corn so that farmers may be able to select among 2,4-D, 

glyphosate, and a mixture of the two for their postemergence broadleaf weed control. 

Farmers will have multiple options to control grass weeds in Dow AgroSciences’ 

herbicide tolerant corn, including soil applied grass herbicides, postemergence

applications of glyphosate, or postemergence applications of quizalofop herbicide. 

Selection pressure for 2,4-D or fop-resistant weed biotypes will be mitigated by the

ability to also use glyphosate concurrently. Since glyphosate still effectively controls 

most grass and broadleaf weed species, use of glyphosate will prevent or delay selection 

for 2,4-D resistance.

Formal herbicide stewardship programs being developed for use with DAS-40278-9 corn 

will provide farmers with the knowledge and tools to optimally manage resistance to 2,4-

D and glyphosate, to ensure the enormous benefits of herbicide-tolerant cropping systems 

can be continued for the long term. Dow AgroSciences’ stewardship program will 

include substantial grower education on cost-effective integrated weed management. An 

extensive network of sales representatives, field scientists, and agronomists will play an 

important role in educating and training applicators and growers on the proper use of the 

technology. Dow AgroSciences field personnel will work with growers to select the seed 

and herbicide products appropriate to their needs.
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Dow AgroSciences LLC

Dow AgroSciences will recommend a program approach for broad-spectrum weed 

control. Pre-plant and preemergence herbicides will be recommended to provide early 

season control of a range of broadleaf and grass herbicides. For example, SureStart®(a 

premix of acetochlor, flumetsulam, and clopyralid) is a residual herbicide that provides a 

broad-spectrum foundation control of grasses and broadleaf weeds and can be applied in 

corn from pre-plant to early postemergence. These herbicide programs provide 

additional modes of action to 2,4-D, quizalofop, and glyphosate and they control several 

weeds that are increasingly problematic in glyphosate tolerant crops, such as horseweed 

(marestail), waterhemp, common lambsquarters, velvetleaf, common and giant ragweed, 

pigweed, morning glory, kochia, and Palmer amaranth.

Dow AgroSciences is voluntarily adopting mode of action labeling for its herbicides that 

can be used with DAS-40278-9 corn, following the WSSA mode of action classification. 

These labels will include clear weed resistance management language promoting 

agronomic practices that reduce the likelihood that resistant weed populations will 

develop and can be used to manage weed resistance if it occurs. These recommendations 

will be product specific, but generally include the use of appropriate herbicide mixtures, 

rotation of herbicides from different mode of action groups, use of burndown and residual 

applications of herbicides at or prior to planting, use of full labeled rates of glyphosate, 

2,4-D and quizalofop when applied, use of alternative weed control practices such as 

delayed planting and use of weed-free crop seeds, and scouting of fields after applications 

for any weeds that may have escaped treatment or show evidence of less-than-expected 

control. Growers will also be asked to report to Dow AgroSciences any incidents of 

repeated non-performance of these herbicides with DAS-40278-9 corn.

In addition to labeling on Dow AgroSciences herbicides, weed resistance management 

practices will be recommended in documentation that accompanies the DAS-40278-9 

seed. As with Dow AgroSciences’ other genetically engineered seed products 

(Herculex®family of insect protection in corn, WideStrike®insect protection in cotton, 

and REFUGE ADVANCEDTM powered by SmartStax®in corn)Dgrowers who purchase 

and plant corn hybrids containing DAS-40278-9 will be required to have a signed Grower 

Agreement in place. The Grower Agreement is a legal and contractual obligation that 

includes a provision requiring them to follow the relevant Product Use Guide. Product 

Use Guides are being developed and will be provided to all growers using the 

technology. These Guides will describe appropriate trait stewardship guidelines 

 

D

SmartStax® multi-event technology developed by Dow AgroSciences and Monsanto. 

TMREFUGE ADVANCED is a trademark of Dow AgroSciences LLC. 

®

SmartStax is a registered trademark of Monsanto Technology LLC.

®TMHERCULEX and the HERCULEX Shield Logo are registered trademarks of Dow AgroSciences LLC

REFUGE ADVANCED is not registered for sale or use in all states.
Supplemental Information for USDA Petition for Nonregulated Status of DAS-40278-9 Corn Page 43 of 50

Dow AgroSciences LLC

including effective weed resistance management based around sound agronomic practices 

and integrated approaches to weed control.

The diversity of herbicide modes of action that can be applied to DAS-40278-9 corn, 

coupled with cultural approaches to weed management, are expected to provide robust 

resistance management and insure long term viability of each of the components. 

Therefore Dow AgroSciences’ DAS-40278-9 herbicide tolerant corn will promote the 

sustainable use and considerable benefits of herbicide tolerant crops.

5 Economic Benefits of Dow AgroSciences Herbicide Tolerant Technology

The introduction of glyphosate tolerant soybeans and corn enabled adoption of 

conservation tillage practices because weeds could be successfully controlled without 

additional tillage. Over the last few years, weed resistance to glyphosate has developed 

and continues to spread. Some weeds can be controlled with other herbicides at an 

additional cost. In some situations, farmers have reverted back from no-till systems to 

conventional tillage or minimum tillage systems in order to control weeds such as 

marestail, giant ragweed and Palmer amaranth incurring not only the cost of additional 

tillage but also losing the positive environmental benefits associated with reduced tillage.

A study was conducted to evaluate the economic impacts of glyphosate resistant weeds 

and herbicide tolerant DAS-40278-9 corn and DAS-68416-4 soybean at the farm level 

through individual case study analysis and to determine the aggregate economic effects at 

the national level using the IHS partial equilibrium models for US crops and farm 

income. The study is presented in Appendix A. Both the case study analysis and 

national analysis utilized scenario analysis to contrast a baseline situation of no weed 

resistance with situations of weed resistance without DAS-40278-9 and DAS-68416-4

technology and weed resistance with DAS-40278-9 and DAS-68416-4 technology.

Glyphosate resistant weed infestations significantly reduce farm income, erode net worth, 

and have significant environmental consequences from tillage changes. The corn case 

studies which did not include tillage impacts for any of the cases show that farmers could 

reduce their farm income impacts from glyphosate resistant weeds by 16 to 19 percent

with DAS-40278-9 technology.

Similar to the case studies, on a national basis herbicide tolerant DAS-40278-9 corn and 

DAS-68416-4 soybean were found in the study to offset over 18 percent of the net farm 

income impacts and eliminate environment impacts saving the equivalent of emissions 

from over 19,000 cars per year and reducing soil erosion by 2.6 million tons per year in 

the United States. Over the 2011 to 2020 period, with DAS herbicide tolerant
Supplemental Information for USDA Petition for Nonregulated Status of DAS-40278-9 Corn Page 44 of 50

Dow AgroSciences LLC

technology, growers would save $4 billion in net farm income and consumers would save 

$563 million.

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

Soybeans on the Cost and Environmental Load of Herbicides Applied on 

Glyphosate Tolerant Corn and Soybeans to Control Glyphosate Resistant and 

Glyphosate Tolerant Weed Biotypes

An analysis was conducted to determine the impact of the use of 2,4-D on herbicide 

tolerant DAS-40278-9 corn and DAS-68416-4 soybeans on the environmental load of 

herbicides applied on glyphosate tolerant corn and soybeans to control glyphosate 

resistant and hard-to-control weed biotypes. Third party proprietary data for corn and 

soybeans and a survey of university weed specialists were used to create assumptions for 

how growers would change herbicide use on glyphosate tolerant corn and soybeans to 

manage glyphosate resistant and hard-to-control weed biotypes. The full analysis is 

presented in Appendix B and the university weed specialist survey is presented in 

Appendix C. Analyses were completed for corn in five states and for soybeans in five 

states targeting control of a glyphosate resistant weed species that are present in each 

state

The analysis indicated that the use of 2,4-D on herbicide tolerant DAS-40278-9 corn for 

control of glyphosate resistant and hard-to-control weed biotypes would reduce the per 

acre environmental load of herbicides applied on glyphosate tolerant corn by 0.15 to 0.74 

lb ai/ac, with an overall average reduction of 0.49 lb ai/ac across all scenarios, compared 

to the use of currently registered alternative non-glyphosate herbicides. Application 

rates of some non-glyphosate alternative herbicides in corn have low rates (examples: 

isoxaflutole, mesotrione, topramezone), however, the pervasive use of acetamide and 

triazine herbicides increases the herbicide environmental load in corn.

Conclusions

Herbicide tolerant crops have played, and continue to play, a central role in improving 

U.S. agricultural productivity and protecting the agricultural environment. Herbicide 

tolerant crops have enabled the widespread adoption of conservation tillage practices that 

preserve soil health, can improve water quality, and improve efficiency of utilization of 

agricultural inputs, while improving weed management and increasing farm income. 

U.S. farmers have enjoyed the benefits of an easy-to-use, flexible, and cost-effective 

weed management technology based around glyphosate. This success has resulted in a 

recent rise in glyphosate resistant weeds and hard-to-control weeds as a consequence of 

over-reliance on a single herbicide mode of action. Alternatives to the glyphosate system 
Supplemental Information for USDA Petition for Nonregulated Status of DAS-40278-9 Corn Page 45 of 50

Dow AgroSciences LLC

that share the same benefits but enable use of alternative modes of action are necessary to 

preserve the benefits of herbicide tolerant crops for the long-term.

Dow AgroSciences has developed an alternative herbicide tolerant technology for corn 

using the aryloxyalkanoate dioxygenase herbicide tolerance gene. Dow AgroSciences’ 

herbicide tolerant DAS-40278-9 corn provides an important alternative to glyphosateonly herbicide tolerance and is a powerful tool that can help solve the challenges of 

weeds that are resistant to, or hard to control with, glyphosate. By enabling the use of 

2,4-D and quizalofop herbicides in addition to glyphosate, DAS-40278-9 corn will allow 

the use of one more tool to control glyphosate resistance. In addition, Dow 

AgroSciences’ herbicide tolerant trait will enable easy implementation of effective weed 

resistance management programs based on pre-mixes, tank mixes, and/or herbicide 

rotation programs that use multiple modes of action to control weed populations. 

Specific stewardship programs to be implemented alongside DAS-40278-9 corn will help 

to preserve glyphosate efficacy and promote 2,4-D weed resistance management.

By offering a simple, effective, and flexible alternative to glyphosate-only herbicide 

tolerant crops, Dow AgroSciences’ herbicide tolerant DAS-40278-9 corn will create the 

opportunity to preserve and extend the many environmental and economic benefits 

farmers have realized from using glyphosate tolerant crops and provide U.S. farmers with 

a cutting edge technology to enhance global competitiveness.

 

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