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Dow AgroSciences LLC dowagro.com

9330 Zionsville Road Indianapolis, IN 46268 USA

308/2E 

February 14, 2013 

Dr. Neil Hoffman 

Science Advisor 

USDA/APHIS/BRS 

4700 River Road, Unit 98 

Riverdale, MD 20737 

Diane Sinkowski 

Senior Environmental Protection Specialist 

USDA/APHIS/BRS 

4700 River Road, Unit 147 

Riverdale, MD 20737 

DAS-68416-4 Soybean and DAS-40278-9 Corn 

Dow AgroSciences Petition Numbers 09-349-01p and 09-233-01p 

SUPPLEMENTARY DOCUMENTATION IN SUPPORT OF ENVIRONMENTAL 

ASSESSMENTS 

Dear Dr. Hoffman and Ms. Sinkowski:

This letter and attached information is in response to your email of Dec.10, 2012 which included a request 

for information from Dow AgroSciences (DAS) to support your efforts in developing the final 

Environmental Assessment and Response to Comments for DAS-402780-9 corn and DAS-68416-4 

soybean. 

The attached information addresses Questions 1, 2 and 3 from Section A. Herbicide Use Issues. 

Herewith, DAS is submitting our response to these questions on the enclosed CD. We are also including a 

Word version of this document. This Word version is intended only for internal use by USDA-APHIS 

staff and not for release.

If you should have any questions or require further information, please contact me at 317-337-3692.

Sincerely,

Gregory L. Orr, Ph.D. 

Global Regulatory Leader 

317-337-3692 

317-337-4649 (fax) 

glorr@dow.com 
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DISTRIBUTION PAGE 

DED Code: D1C / B1C 

bcc: Laura Tagliani, 308/2E 

Greg Orr, 308/2E 

Heidi Reistad, 308/2E 

Federal Action Files, 308/2E unstapled
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Table of Contents

Section A. Herbicide Use Issues

Questions 1 2, 3

Herbicide Use Trends in US Soybeans and Corn ....................................................4 

Soybean Herbicide Use Trends..........................................................................6 

Corn Herbicide Use Trends.............................................................................17

Timing of 2,4-D Application in Key Crops......................................................... 24 

Total Herbicide Use Trends of the Major Active Ingredients Used in Corn and Soybeans....27

Timing of Use of the Different Active Ingredients in Corn and Soybean Crops ...............31 
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DOW AGROSCIENCES RESPONSE TO USDA-APHIS QUESTIONS RECEIVED 

DECEMBER 10, 2012 REGARDING DAS-40278-9 CORN AND DAS-68416-4 SOY.

A. Herbicide use issues

1. What herbicide active ingredients have been used on corn and soybean since 1990. If this 

information is available on a state basis, it would be useful to send it to us state by state 

because we need to do a regional analysis in the cumulative impacts as well as a national 

analysis. 

2. For each active ingredient, list the total pounds used in each season data is available for 

a. Corn

b. Soybean

c. all agricultural use

d. all non agricultural use. 

3. If data is available, list the amounts used as either 

a. preplant burndown/pre emergent use

b. post-emergent use

Herbicide Use Trends in US Soybeans and Corn

This section focuses on the top 10 herbicides by pounds of active ingredients and the trends in 

use for the crops of interest. A discussion of general herbicide use and practices is provided in 

our response to Section B on 2,4-D use (submitted to USDA via email on Jan.. 24, 2013 and Feb. 

1, 2013). The data in this section have been obtained from public sources (as indicated in the 

document) and any additional data was obtained from third party proprietary sources as survey 

response data.

Growers in the US have been quick and significant adopters of genetically introduced traits 

(Figure 1). Adoption of herbicide tolerant crops has been rapid and almost universal, particularly 

for soybean and cotton. Adoption of herbicide tolerant varieties in corn has also been strong but 

somewhat slower, likely due to an emphasis growers place on elite yielding hybrids, greater 

number of herbicide options and slower emergence of glyphosate resistant weeds in the greater 

corn belt.

The acres in the Conservation Reserve Program (CRP) have declined approximately 10 million 

acres over the past ten years, as the government has scaled back the program. This has helped 

fuel an increase in planted corn acreage which has trended upward in response to the attractive 

profit opportunity for the US farmer to supply the strong demand for feed, fuel and exports 
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(Figure 2). Soybeans have also gained acreage while wheat has declined in area planted in the 

US.

Figure 1. Adoption of genetically engineered crops in the United States 1997-2012

http://www.ers.usda.gov/data-products/adoption-of-genetically-engineered-crops-in-the-us.aspx
6 of 33

Figure 2. Acreage planted to corn, soy and wheat in the US.

http://www.fas.usda.gov/psdonline/psdhome.aspx

Herbicides are used at different times in the various market segments depending on the 

properties of the active ingredient (a.i.), the susceptibility of the crop and the nature of the weed 

problems. The terms “pre” or “preemergence” and “post” or “post emergence” refer to the stage 

of the crop’s emergence from the soil. 

Residual herbicides work by controlling weeds before they germinate or emerge. These 

compounds are applied prior to planting or prior to crop emergence in most cases. When 

weather complicates the timing of herbicide applications with planting, growers may plant and 

apply the residual herbicide in a mix with a foliar applied product. The foliar product controls 

emerged weeds while the residual material controls weeds prior to germination or emergence.

Soybean Herbicide Use Trends

The trend in soybean herbicide use changed dramatically with the introduction of Roundup 

Ready® (RR) soybeans. As shown in Figure 1, RR soybeans had the most rapid adoption curve 

of the transgenic crops and by 2003 were planted on 80% of the US soybean acres. The adoption 

of RR soybeans allowed post emergent application of a systemic herbicide (glyphosate) that 

controlled most grasses and broadleaves. This required much less time and was simpler to 

implement than using incorporated pre-plant herbicides which require different rates for different 

soil types and pH. The speed of adoption was enhanced by the fact that the use of glyphosate on 
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post emergent RR soybeans cost less than many farmers had been spending on weed control in 

soybeans as well as delivering better weed control.

Prior to the introduction of RR soybeans, farmers used many different active ingredients, both 

residual and post emergent herbicides, to control the varied weed problems that existed in corn 

and soybeans . Growers used these different products sequentially or in combination. For 

example, trifluralin or metolachlor was used to target grass weeds and some broadleaf weeds. 

Other products, such as metribuzen, targeted broadleaf weeds. The ability to use glyphosate over 

the top of soybeans allowed farmers to target both grass and broadleaves with one product that 

only required an average of 1.5 applications. This had the added benefits of using a single rate 

across soil types or pH and did not require either mechanical incorporation into the soil or 

rainfall for activation. This proved an attractive option for farmers that allowed a simpler 

solution and also gave a better weed control result in many cases. The use of glyphosate post 

emergent on RR soybeans worked very well because soybeans are usually planted in narrow 

rows which provide rapid canopy closure thereby preventing most weeds from germinating. The 

benefit of total post emergent weed control also supported adoption of no till practices, saving 

time and money for the grower while reducing soil erosion.

Top 10 Soybean Herbicides (total pounds applied)

As stated above, the data utilized in this section have been obtained from third party proprietary 

sources. Glyphosate accounted for 81% of all herbicide active ingredient pounds used in US 

soybeans during 2011 and accounted for 113 million treatment acres (Figure 3.). The top 10 

herbicides (by pounds used), account for 97% of total herbicide pounds used in US soybeans in 

2011. As the figure below shows, the pounds of glyphosate active ingredient grew to over 100 

million pounds per year in soybeans and replaced much of the other herbicides that had been 

used. The sharp increase in 2008 was due to the large increase in soybean acres that year.
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Figure 3. Top 10 Soybean Herbicides 1990-2011

Top 10 Soybean Herbicides (treated acres)

Evaluating treated acres within crop by the different actives (Figure 4) provides a better 

comparison of the relative use of the herbicides than focusing on pounds applied due to 

differences in use rate between actives and trends in use rate over time.
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Figure 4. Top 10 Soybean Herbicides 1990-2011

Removing glyphosate from the analysis provides a clearer picture of the other soybean 

herbicides used over time (Figure 5), indicating that chlorimuron and flumioxazin were the 

second and third most common herbicide treatments in soybeans in the US in 2011. From 2008 a 

clear trend towards including additional herbicides in soybean weed control programs can be 

seen. This is related to the increasing emergence of hard to control weeds and glyphosate 

resistant weeds, with additional herbicides being used to control them plus prevent the 

emergence of additional resistant weeds. 
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Figure 5. Top 9 Soybean Herbicides 1990-2011

Regional Use of Herbicides in Soybean by US Cropping Region

The U.S. states can be divided into agricultural regions as shown in the map below (Figure 6). 

Overall, the herbicides used to control weeds in soybean are similar across regions (Figures 7-

16). Glyphosate provides the principal basis for weed control in each of the regions with other 

actives being used to control weeds that are not controlled satisfactorily by glyphosate alone. 

The Heartland Region accounts for half of all soybean herbicide treatments (data not shown). 

Some of the increase in herbicide use has been tied to an increase in soybean acreage. This is 

especially true in the Northern Great Plains Region which has seen acres of corn and soybeans 

increase greatly in the past 5 years (data not shown).

The trends have been similar across the regions with the use of other products starting to trend 

upward again as weed control has slipped in recent years with some weeds developing increased 

tolerance or resistance to glyphosate and ALS compounds (ex., chlorimuron, thifensulfuron). 

Soybean growers are responding by using other products either in combination or sequentially 

with glyphosate. In the Heartland region, 2,4-D use in burndown applications started increasing 

in 2008 (Figures 7 and 8). In the southern regions, a number of products have increased in use 

led by metolachlor-S and 2,4-D (Figures 15 and 16). The SouthEast region has seen weed 

resistance to glyphosate develop the most rapidly and this is likely causing the more rapid 

change in herbicide use patterns compared to the other regions. The use of fomesafen, 
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flumioxazin, chlorinuron, Metolachlor-S and 2,4-D have all increased rapidly since 2008 as 

farmers strive to get control of weeds that are not being controlled adequately by glyphosate 

treatments (Figure 16).

Figure 6. U.S. States Grouped Into Regions

States Grouped into Regions
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Figure 7: Top 10 Soybean Herbicides (total lbs applied) in the Heartland Region

Figure 8: Top 10 Soybean Herbicides (treatment acres) in Heartland
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Figure 9: Top 10 Soybean Herbicides (total lbs applied) in the Northern Crescent 

Figure 10: Top 10 Soybean Herbicides (treatment acres) in the Northern Crescent
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Figure 11: Top 10 Soybean Herbicides (total lbs applied) in the Northern Great Plains

Figure 12: Top 10 Soybean Herbicides (treatment acres) in the Northern Great Plains 
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Figure 13: Top 10 Soybean Herbicides (total lbs applied) in the Prairie Gateway Region

Figure 14: Top 10 Soybean Herbicides (treatment acres) in the Prairie Gateway
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Figure 15: Top Soybean Herbicides (total lbs applied) in the SouthEast

Figure 16: Top Soybean Herbicides (treatment acres) in the SouthEast
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Corn Herbicide Use Trends

Corn yields are more negatively impacted by early season weed competition than soybeans. 

Corn is also planted in wider rows than soybeans and the resulting penetration of light allows 

weed germination over a longer period of time than soybeans. As a result, most corn growers 

have continued to use residual herbicides followed by application of post emergent herbicides as 

needed to provide good weed control and maximize yield potential. Some growers have reduced 

rates of residual herbicides since they have good post emergent options to clean up later 

germinating weeds.

Top 10 Corn Herbicides 

Glyphosate is the top herbicide active ingredient used in corn, accounting for roughly 40% of the 

pounds of active used (Figure 17). The top 10 actives account for over 97% of all of the pounds 

a.i. used in corn in the US in 2011. However, glyphosate did not replace the other actives in corn 

to the extent it did in soybeans. Rather, it was used in combination to improve weed control. 

Note that one of the larger products in the early 90’s was alachlor, which does not show in this 

chart (Figure 18). Alachlor was displaced by acetochlor which has the same mode of action but 

can be used at a lower rate.

Figure 17. Top 10 US Corn Herbicides (total lbs applied)

0

10,000,000

20,000,000

30,000,000

40,000,000

50,000,000

60,000,000

70,000,000

80,000,000

90,000,000

Total lbs AI

Top Herbicides in US Corn 2011

GLYPHOSATE ATRAZINE ACETOCHLOR METOLACHLOR-S

2,4-D METOLACHLOR SIMAZINE MESOTRIONE

DICAMBA DIMETHENAMID-P

ss
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Figure 18. Top 10 US Corn Herbicides (treatment acres)

The trends in corn herbicide use reflect the adoption of Roundup Ready® corn (launched in 

1998) and the resulting increase in the use of glyphosate. The use of other actives declined 

somewhat until about 2008 and then began to increase again. This was in response to the 

increased value of the crop due to the high price of corn and the appearance of hard to control 

and glyphosate resistant weeds. The trends are similar across the regions (Figure 6), but all 

regions (Figures 19-28) show an increase in more modes of action being employed (photosystem 

II, ALS, mitotic, and carotenoid biosynthesis inhibitors). The increases are primarily in the 

broadleaf and cross spectrum products, with mesotrione, 2,4-D and dicamba increasing as well as 

metolachlor and acetochlor.
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Regional Use of Herbicides in US Corn 

 Figure 19. Top 10 US Corn Herbicides (total lbs applied) in the Heartland Region

Figure 20. Top 10 US Corn Herbicides (treatment acres) in the Heartland Region

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

30,000,000

35,000,000

40,000,000

45,000,000

Total lbs AI

Corn Herbicide Trends - Heartland Region

GLYPHOSATE ATRAZINE ACETOCHLOR METOLACHLOR-S

2,4-D SIMAZINE MESOTRIONE METOLACHLOR

DIMETHENAMID DIMETHENAMID-P

ss
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Figure 21. Top 10 US Corn Herbicides (total lbs applied) in the Northern Crescent

Figure 22. Top 10 US Corn Herbicides (treatment acres) in the Northern Crescent
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Figure 23. Top 10 US Corn Herbicides (total lbs applied) in the Northern Great Plains

Figure 24. Top 10 US Corn Herbicides (treatment acres) in the Northern Great Plains
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Figure 25. Top 10 US Corn Herbicides (total lbs applied) in the Prairie Gateway

Figure 26. Top 10 US Corn Herbicides (treatment acres) in the Prairie Gateway
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Figure 27. Top 10 US Corn Herbicides (total lbs applied) in the SouthEast

Figure 28. Top 10 US Corn Herbicides (treatment acres) in the SouthEast

0

1,000,000

2,000,000

3,000,000

4,000,000

5,000,000

6,000,000

7,000,000

8,000,000

Total lbs AI

Corn Herbicide Trends in Pounds - SouthEast 

GLYPHOSATE ATRAZINE METOLACHLOR-S 2,4-D SIMAZINE

PARAQUAT DICAMBA MESOTRIONE ALACHLOR METOLACHLOR

ss
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Timing of 2,4-D Application in Key Crops

Late fall and the period prior to planting account for all of the 2,4-D applications to soybeans 

(otherwise it would kill the soybeans) and the vast majority of 2,4-D treatments to corn (Figures 

27, 28).

Much of the 2,4-D herbicide use in corn and soybeans is focused on controlling difficult to 

control weeds or preventing resistance development. The use in burndown applications prior to 

planting helps establish a clean seedbed and reduce early season competition without a tillage 

operation. Some applications are also done the previous fall to clean up weed escapes (including 

any potentially resistant weeds) in the prior crop and/or to control winter annuals.

Figure 29. 2,4-D Application Timing: Soybean
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Figure 30. 2,4-D Application Timing: Corn

Corn often follows soybeans in rotation, which are generally harvested earlier in the fall, 

allowing more time for weed growth prior to winter. Usually corn planting begins earlier in the 

spring than soybean planting. Thus, there is less opportunity for weed emergence prior to 

planting corn which decreases the weeds that can be controlled with a spray application prior to 

planting. Both of the factors drive growers to make a fall application(s) to control weeds before 

planting corn the next season.

In winter wheat, roughly 20% of 2,4-D is applied in the fall or at plant to provide early weed 

control (Figure 31). However, the vast majority is applied the following spring after the wheat 

and the new crop of weeds are actively growing.

Winter wheat, being planted in the fall of the year, provides the crop with a large advantage over 

many of the weeds that germinate in the spring. In crop seasons with favorable conditions, the 

wheat establishes a dense stand and tillers to form a canopy that prevents light penetration, thus 

preventing many weeds from germinating. This is one of the major factors that allow almost half 

of winter wheat in the US to be successfully grown without a single herbicide application. 

In Spring Wheat, roughly 20% of 2,4-D applications occur prior to or at planting with the 

remaining treatments usually more than 3 weeks after crop emergence (Figure 32). This allows 

the wheat to get established and form a canopy. Weeds germinate and begin to establish during 

this early part of the season and are most vulnerable to a herbicide application at this time. 

Late post is defined as more then 3 

weeks after emergence 
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Figure 31. 2,4-D Application Timing: Winter Wheat

Figure 32. 2,4-D Application Timing: Spring Wheat
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Total Herbicide Use Trends of the Major Active Ingredients Used in Corn and Soybeans

Historical use of major agricultural herbicides for corn and soybean is shown in Figure 33. 

Glyphosate has developed into the predominant herbicide in both crops in the last 10 years. For 

historical sake, alachlor is included even though it is not currently used. 

Glyphosate is by far the most utilized herbicide in US agriculture. Many of the active ingredients 

do not have large enough usage to show up on the chart and several of the ones that did, have 

declined dramatically over time including alachlor, metolachlor, trifluralin and pendimethalin. 

The introduction of metolachlor-S and acetochlor caused much of the reduction in alachlor and 

metolachlor use. All of these actives are residual herbicides that provide control for an extended 

period of time by preventing weeds from emerging. 

Figure 33. Major Corn and Soybean Actives Total Use in Agriculture

Herbicide Use in the Different Market Segments

Of the active ingredients shown in Figure 33, only a few have a significant portion of their use in 

non-crop markets. These actives are 2,4-D, glyphosate, clopyralid, dicamba, and pendimethalin 

(Figures 34-38). There are three major market segments of 2,4-D use: agricultural crop use, 

range and pasture use, and non-crop use. The use of 2,4-D (and all other herbicides in Fig. 33) 

varies from year to year depending on the respective area planted to different crops and the 

weather conditions that occur during the year which will influence crop and weed development. 

0

50

100

150

200

250

300

Million Pounds ai

Total Agricultural Use of Major Corn and Soybean Herbicides 

1990

1995

2000

2005

2011

d

r
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The non-crop segment use also depends on weather conditions, with use declining during 

drought years when lawns and rights-of-way dry up. The range of use of 2,4-D across all 

segments varies from 58-68 million pounds with an average of 64 million pounds ai based on 

information from several proprietary sources and internal company expertise. 

The agricultural segment is made up of the crop use segment and the range and pasture segment. 

Within the crop segment these uses are very diverse ranging from burndown application prior to 

planting soybeans, to use underneath tree crops and use on wheat. The range and pasture 

segment consists of control of annual weeds as well as control of perennial weeds, woody and 

invasive species.

The non-crop segment includes use on rights of ways for roadways, utilities and railroads, 

nurseries, forestry, lawns, cemeteries, and other uses to control undesirable plants.

Figure 34. 2,4-D Use by Market Segment

2011 Use of 2,4-D by Pounds Active

Crops

Range & Pasture

Non-Crop
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Figure 35. Glyphosate Use by Segment 2011

Figure 36. Clopyralid Use by Segment 2011

Glyphosate Use by Segment 2011

Crop Use

Range & Pasture

Non Ag

Clopyralid Use by Segment

Crop Use

Range & Pasture

Non Ag
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Figure 37. Pendimethalin Use by Segment 2011

Figure 38. Dicamba Use by Segment 2011

Pendimethalin Use by Segment 2011

Crop Use

Range & Pasture

Non Ag

Dicamba Use by Segment 2011

Crop Use

Range & Pasture

Non Ag
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Timing of Use of the Different Active Ingredients in Corn and Soybean Crops

Herbicides are used at different times in the various market segments depending on the 

properties of the active ingredient, the susceptibility of the crop and the nature of the weed 

problems (Figures 39-42). The terms “pre” or “preemergence” and “post” or “post emergence” 

refer to the stage of the crop’s emergence from the soil. Non-applicable (NA) refers to perennial 

crops, examples are tree crops, pasture, sugarcane and hay crops or fallow where there is no 

crop.

Residual herbicides such as acetochlor, trifluralin, metolachlor, metolachlor-S, pendimethalin, 

acetochlor, atrazine and alachlor work by controlling weeds before they germinate or emerge. 

These compounds are applied prior to planting or prior to crop emergence in most cases. When 

weather complicates the timing of herbicide applications with planting, growers may plant and 

apply the residual herbicide in a mix with a foliar applied product, such as acetochlor combined 

with glyphosate applied to corn. The foliar product (glyphosate in this example) controls 

emerged weeds while the residual material (acetochlor) controls weeds prior to germination or 

emergence.

The post materials have activity when foliar applied to plants and can be used over the top of 

crops if the crop is selective for that active or has been modified to be tolerant (ex., RR corn and 

RR soybeans). If the crop is not tolerant the active may still provide useful weed control by using 

the herbicide prior to the crop emerging (pre-emergence application). Burndown applications in 

both crops often incorporate glyphosate, diacamba,and 2,4-D and may include paraquat or 

glufosinate to control weeds prior to crop emergence. Most of the actives will have some use in 

both corn and soybeans, but a few are used in only corn or soybeans. Atrazine, mesotrione and 

simazine are not used on soybeans and imazethapyr, fomesafen, chlorimuron, flumioxazin and 

trifluralin are predominantly used on soybeans.
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Figure 39. Timing of Use for 2,4-D, Acetochlor, Atrazine, and Dicamba

Figure 40. Timing of Use for flumetsulam, fomesafen, glufosinate, glyphosate and imazethapyr

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

NA POST PRE NA POST PRE NA POST PRE NA POST PRE

2,4-D Acetachlor Atrazine Dicamba

Timing of Active Use

1990

1995

2000

2005

2011

0

0.2

0.4

0.6

0.8

1

1.2

NA

POST

PRE

NA

POST

PRE

NA

POST

PRE

NA

POST

PRE

NA

POST

PRE

Flumetsulam Fomesafen Glufosinate Glyphosate Imazethapyr

Timing of Active Use

1990

1995

2000

2005

2011
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Figure 41. Timing of Use for Isoxaflutole, Mesotrione, Metalachlor and Metolachlor-S

Figure 42. Timing of Use for Pendimethalin, Thifensulfuron, Trifluralin and Paraquat

0

0.2

0.4

0.6

0.8

1

1.2

NA POST PRE NA POST PRE NA POST PRE NA POST PRE

Isoxaflutole Mesotrione Metolachlor Metolachlor-S

Timing of Active Use

1990

1995

2000

2005

2011

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

NA POST PRE NA POST PRE NA POST PRE NA POST PRE

Pendimethalin Thifensulfuron Trifluralin Paraquat

Timing of Active Use

1990

1995

2000

2005

2011