Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 1 of 53 

Supplemental Information to Support the NEPA Analysis for the Determination of 

Nonregulated Status of Dicamba-Tolerant Soybean MON 87708 and Dicamba- and 

Glufosinate-Tolerant Cotton MON 88701 

Impact and Benefits of Dicamba-Tolerant Soybean and Dicamba and Glufosinate-Tolerant 

Cotton on Weed Resistance Management 

OECD Unique Identifiers: MON-877Ø8-9 (soybean) and MON-887Ø1-3 (cotton) 

Monsanto Petition Numbers: 10-SY-210U (soybean) and 12-CT-244U/ 12-CT-244U-S (cotton) 

USDA Petition Numbers: 10-188-01p (soybean) and 12-185-01p_a1 (cotton) 

January 17, 2014 

Submitted by: 

Rhonda M. Mannion, B.S. 

Monsanto Company 

800 North Lindbergh Blvd. 

St. Louis, MO 63167 

Phone: (314) 694-8785 

Fax: (314) 694-3080 

E-mail: rhonda.m.mannion@monsanto.com

Prepared by: 

J.K. Soteres, Ph.D. and R.M. Mannion, B.S. 

Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 3 of 53 

Table of Contents

Introduction and Background......................................................................................................... 4

Background – Legal ...................................................................................................................................5

Background – Herbicide Use..................................................................................................................... 6

Benefits of DT Soybean and DGT Cotton for Weed Control and Resistance Management......... 10

Dicamba Resistance: Potential ..................................................................................................... 12

Impact of Dicamba Resistance...................................................................................................... 13

Results and Discussion.................................................................................................................. 14

Current Dicamba Uses and Identification of Highest Risk Areas.................................................. 14

Dicamba Weed Targets........................................................................................................................... 16

Weed Management Systems for Current Dicamba Uses ....................................................................... 17

Herbicide Options to Control Weeds in Current Dicamba Crop Uses .................................................... 17

Scope and Impact of Existing Dicamba Resistant Species ...................................................................... 18

Weed Resistance Management Stewardship ......................................................................................... 19

Conclusions................................................................................................................................... 19

Appendix A.................................................................................................................................... 41

Appendix B.................................................................................................................................... 44

References .................................................................................................................................... 49
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Introduction and Background

Monsanto has developed a new biotechnology-derived soybean (Glycine max), designated as 

event MON 87708 (“DT soybean”), that is tolerant to dicamba herbicide, and a new 

biotechnology-derived cotton (Gossypium spp.), designated as event MON 88701 (“DGT 

cotton”), that is tolerant to dicamba and glufosinate herbicides. Monsanto submitted petitions for 

determinations of nonregulated status for DT soybean and DGT cotton three and one years ago, 

respectively, and has provided the U.S. Department of Agriculture (USDA) Animal and Plant 

Health Inspection Service (APHIS) with lengthy scientific materials and Environmental 

Reports.1,2 This document addresses the impact and benefits of DT soybean and DGT cotton on 

weed resistance management. As discussed herein, the approval of DT soybean and DGT 

cotton, will provide growers with an important new tool to manage weeds and mitigate the 

further evolution of resistance to some current U.S. herbicides. 

Associated with the cultivation of DT soybean and DGT cotton will be an increase in use of 

dicamba, which will potentially result in increased selection pressure for resistant biotypes. This 

risk can be significantly mitigated by incorporating dicamba into a diversified weed management 

program. To evaluate this risk Monsanto has conducted an analysis to understand the risk of 

cross-over resistance (i.e., resistance that may evolve in soybean or cotton and then impact other 

dicamba crop uses) by evaluating: (1) the primary weed targets and the current extent of 

dependence on dicamba for weed management, and (2) the potential overlap of weed species 

across these cropping systems. Overall, the analysis indicates that risk of cross-over resistance is 

low, and because of the low dependency of farmers on dicamba for weed management in these 

areas combined with the availability of other herbicide options, the potential socio-economic 

impact of cross-over resistance would be low. 

                                                           

1

 Petition for the Determination of Nonregulated Status for Dicamba-Tolerant Soybean MON 87708, Monsanto Petition Number: 

10-SY-201U (July 6, 2010) ; Supplemental Information to Support the NEPA Analysis for the Determination of Nonregulated 

Status of Dicamba-Tolerant Soybean MON 87708, Petition # 10-188-01p (Oct. 11, 2012); Supplemental Information to 

Support the NEPA Analysis for the Determination of Nonregulated Status of Dicamba-Tolerant Soybean MON 87708, Petition 

# 10-188-01p (Dec. 14, 2012); Supplemental Information to Support the NEPA Analysis for the Determination of 

Nonregulated Status of Dicamba-Tolerant Soybean MON 87708, Petition # 10-188-01p (Jan. 31, 2013); Petitioner’s 

Environmental Report for Dicamba-Tolerant Soybean MON 87708 and Dicamba- and Glufosinate-Tolerant Cotton MON 

88701, Monsanto Petition Numbers 10-188-01p and 12-185-01p_al) (Nov. 25, 2013). 2

 Petition for the Determination of Nonregulated Status for Dicamba and Glufosinate-Tolerant Cotton MON 88701, Monsanto 

Petition Number: 12-CT-244U (July 2, 2012); Petitioner’s Environmental Report for Dicamba and Glufosinate-Tolerant 

Cotton MON 88701, Monsanto Petition Number: 12-CT-244U-S (USDA Petition #12-185-01p_al) (May 6, 2013); 

Petitioner’s Environmental Report for Dicamba-Tolerant Soybean MON 87708 and Dicamba- and Glufosinate-Tolerant Cotton 

MON 88701, Monsanto Petition Numbers 10-188-01p and 12-185-01p_al) (Nov. 25, 2013). 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 5 of 53 

Background – Legal

On May 16, 2013, APHIS announced its intention to prepare a full Environmental Impact 

Statement (EIS) not only to address jurisdictional plant pest issues under the Plant Protection Act 

(PPA), but also to examine the possible environmental impacts of dicamba herbicide uses, 

including the potential for development of herbicide-resistant weeds.3 As discussed in previous 

submissions to APHIS, Monsanto does not believe that addressing the impacts of herbicide uses 

in an EIS, as described by APHIS’s May 16, 2013 Notice of Intent (NOI), is required by the 

National Environmental Policy Act (NEPA) or any other law. 

First, the PPA does not give APHIS regulatory authority over herbicide uses or impacts, or to 

address herbicide resistance. Indeed, Congress expressly transferred regulatory authority over 

herbicides from APHIS to EPA over four decades ago4, and APHIS itself has long recognized 

the strict limits on its PPA authority.5 On the other hand, EPA’s authority to regulate herbicides 

under FIFRA includes an evaluation of, and measures to address, the development of herbicide 

resistance in weeds associated with the use of those products.6

 Accordingly, APHIS has no 

jurisdiction over herbicides or the development of herbicide resistance in weeds that may be 

associated with herbicide use, and no authority to consider herbicide impacts under the PPA. 

Consequently, APHIS has no obligation under NEPA to consider herbicide resistance in weeds 

(or any other environmental impacts of dicamba or glufosinate use, or to consider alternatives to 

deregulation based on these factors) as “effects” since there is no reasonable alternative to 

deregulation once APHIS finds DT soybean and DGT cotton do not pose a greater plant pest risk 

than their conventional counterparts.7 As discussed in previous documentation submitted to 

APHIS, this longstanding understanding of NEPA was recently confirmed by the U.S. Court of 

Appeals for the Ninth Circuit.8 

It is likewise inappropriate for APHIS to identify weed resistance as a “cumulative impact” 

under 40 C.F.R. §1508.7. As discussed above, any decisions regarding restrictions of the use of 

                                                           

3

 78 Fed. Reg. 28796. 

4 Ruckelshaus v. Monsanto Co., 467 U.S. 986, 991(1984) (observing that “the Department of Agriculture’s FIFRA 

responsibilities were transferred to the then newly created Environmental Protection Agency....”); see also Pub.L. No. 92-516, 

86 Stat. 973 (1972). 

5 See Center for Food Safety v. Vilsack, 718 F.3d 829, 840 (9th Cir. 2013). 6 See, e.g., EPA, Pesticide Registration (PR) Notice 2001-5, “Guidance for Pesticide Registrants on Pesticide 

Resistance Management Labeling,” p. 2 (2001), available at http://www.epa.gov/PR_Notices/pr2001-5.pdf 

(labeling measures to assist in pesticide resistance management). Additionally, pesticide registrants must report 

resistance to EPA as an adverse effect in order to ensure the pesticide continues to meet FIFRA requirements for 

registration. 40 C.F.R. § 159.188(c). 7 DOT v. Public Citizen, 541 U.S. 752, 770, 769 (2004) (where an agency has no ability to prevent a certain effect 

due to its limited statutory authority over the relevant actions, the agency cannot be considered a legally relevant 

“cause” of the effect, and is therefore not required to analyze the environmental impact of an action it could not 

refuse to perform). 8

 For further discussion of the litigation, see Section I.B.4 of Petitioner’s Environmental Report for DicambaTolerant Soybean MON 87708 and Dicamba- and Glufosinate-Tolerant Cotton MON 88701, Nov. 25, 2013. 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 6 of 53 

dicamba (including any such measures related to weed resistance) are within the sole purview of 

EPA; APHIS has no control whatsoever over the nature of any such restrictions. Lacking such 

control, APHIS is not required to address the EPA decision on dicamba, or the consequences of 

such decision, as cumulative impacts.9

 In short, any weed resistance impacts associated with 

herbicide uses are not caused by APHIS’s PPA determinations, and cannot trigger a need to 

perform NEPA review in connection with a PPA determination. And, of course, weed resistance 

and any responses thereto, cannot constitute significant environmental impacts of an APHIS PPA 

determination. Indeed, multiple federal courts have held that EPA’s review under FIFRA is the 

“functional equivalent” of NEPA.10 Thus, APHIS’s review of resistance issues would duplicate 

the NEPA-equivalent analyses already being performed by EPA under its authorities. 

If APHIS intends nevertheless to include such material in its EIS, it should make clear that it is 

exercising its discretion to perform that analysis in the document, not that it is legally required to 

include that material under NEPA or any other statute. 

Background – Herbicide Use

In the decades since the introduction of the first herbicide (2,4-D) for weed control in corn in 

early 1940s, herbicide use has become a critical agronomic tool that is used on the vast majority 

of cropland in the United States. By 1962, farmers had access to approximately 100 herbicides 

available in approximately 6000 formulations. According to a 2006 study, farmers routinely use 

herbicides on more than 90% of the area of most crops grown in the U.S. (Gianessi and Reigner 

2006). 

Weed control in crop production is essential for optimizing yields because weeds compete with 

crops for light, nutrients, and soil moisture. Weeds can also harbor insects and diseases, and can 

interfere with harvest, causing extra wear on harvest equipment. A study by CropLife America 

demonstrated that in 2005 the use of herbicides saved U.S. farmers 337 million gallons of fuel, 

produced $16 billion in crop yield increases, and cut weed control costs by $10 billion as 

compared to production without the use of herbicides (Gianessi and Reigner 2006). 

Additionally, without herbicides growers would have to abandon no-till and other conservation 

tillage production practices, which reduce soil erosion. If U.S. growers stopped using herbicides 

and resumed tillage on the number of acres not tilled in 2005, an additional 356 billion pounds of 

                                                           

9

 DOT v. Public Citizen, 541 U.S. 753, 767 (2004). 10 Envtl. Def. Fund, Inc. v EPA, 489 F.2d 1247, 1256 (D.C. Cir. 1973) (holding that FIFRA’s standard and processes 

are the “functional equivalent of a NEPA investigation” and that “[t]he law requires no more”); Envtl. Def. Fund, 

Inc. v. Blum, 458 F. Supp. 650, 662 n.6 (D.D.C. 1978) (“If the ‘functional equivalent’ requirement means 

anything, it surely means that the EPA [in conducting analysis under FIFRA] did not have to follow the detailed 

procedural requirements laid out by NEPA.”); Douglas Cnty. v. Babbitt, 48 F.3d 1495, 1502-03 (9th Cir. 1995) 

(“FIFRA for NEPA to apply to FIFRA.”); Merrell v. Thomas, 807 F.2d 776, 782 (9th Cir. 1986) (“FIFRA’s 

review provisions do afford the public some opportunity to participate in pesticide registration decisions.... [And 

while that] opportunity would be greater if NEPA [also] applied[,] Congress has made its choice [not to do so].”). 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 7 of 53 

sediments would be deposited in streams and rivers, resulting in an estimated $1.4 billion in 

downstream damage (Gianessi and Reigner 2006). 

Throughout the 70-year history of herbicide use, farmers have regularly dealt with resistance 

issues as herbicide uses have resulted in natural selection of existing tolerant weeds within weed 

populations. In fact, resistance is a natural and ordinary occurrence that, over time, the 

agricultural community has addressed by making adjustments to cultivation practices. 

As noted by prominent weed scientists, the most effective crop weed management programs use 

a combination of cultural, mechanical, and/or herbicide control practices, called diversified weed 

management practices, instead of relying on one particular method of weed control (Beckie, et 

al. 2011; Hake, et al. 1996; Norsworthy, et al. 2012; University of California 2009; Vargas, et al. 

1996). Examples of methods that can be used in a diversified weed management program 

include: (1) use multiple herbicides in mixtures, sequences, or rotation, (2) use mechanical tillage 

such as timely mowing or tillage, and/or (3) cultural practices such as crop rotation or other 

agronomic practices to increase crop competitiveness (WSSA Resistance management training 

modules at wssa.net). 

The emergence of certain herbicide-resistant weeds over the past decade, including 

glyphosate-resistant weed biotypes in certain areas of the U.S., is simply another chapter in the 

history of herbicide uses. As has been the case in the past, natural selection of tolerant weeds 

has meant that growers have needed to continue to adapt and implement evolving weed 

management strategies. These types of adaptations in resistance management strategies are not 

new as weed resistance has occurred for decades. As of January 2014, 416 herbicide-resistant 

weed biotypes have been reported to be resistant to 21 different herbicide modes-of-action 

worldwide (Heap 2014d). Glyphosate-resistant weeds, which occur in certain areas of the U.S., 

account for approximately 6% of U.S. herbicide-resistant biotypes, while weeds resistant to 

herbicides that inhibit acetolactate synthase (ALS) and photosynthesis at photosystem (PSII) 

inhibitors account for 33% and 17% of the herbicide-resistant biotypes, respectively (Heap 

2014e). Dicamba-resistant and glufosinate-resistant weeds account for 1% and 0.5% of resistant 

biotypes respectively (Heap 2014f; g). Again, resistance occurs naturally in weed populations, 

and the use of herbicides selects for the resistant plants within a population. As discussed further 

below, Monsanto continues to rely upon the consensus recommendations of leading academic 

weed scientists who, for several years, have recommended multiple modes of action. 

Where necessary to manage herbicide-resistant weeds in soybean and cotton production, growers 

in certain areas of the U.S. have increased herbicide application rates, increased the number of 

herbicides (number of modes of action), and, in some cases, returned to more traditional tillage 

practices (Monsanto 2013a) and hand-weeding (Culpepper, et al. 2011; NRC 2010). In an effort 

to manage glyphosate-resistant Palmer amaranth, certain non-glyphosate herbicides have been 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 8 of 53 

reported as being used in conditions and practices that have the potential to result in increased 

selection of resistant biotypes to those herbicides, thereby putting certain agricultural herbicides 

in some major herbicide classes at risk (Nichols, et al. 2010; Prostko 2011) (Dr. Larry Steckel 

and Dr. Stanley Culpepper, personal communications, August 2012). While effective options for 

managing Ambrosia spp., and Amaranthus spp., including Palmer amaranth, waterhemp and 

other key broadleaf weeds exist, weed scientists have concluded that there is a need for 

additional herbicide modes-of-action (MOA) to mitigate the potential for development of 

resistance to the key herbicides essential for weed management in soybean and cotton (Tranel, et 

al. 2010). 

In addition, there has been an increase in the detection of weed populations with resistance to 

multiple herbicide modes-of-action (multiple resistance) in certain weed species, for example, 

Amaranthus spp. (Tranel et al. 2010). This development further highlights the need for 

additional modes of action on certain species. Presently there are six broadleaf species known to 

have populations with multiple resistance in the U.S., thus limiting the number of herbicide 

options available for weed control in fields where these populations exist (see Table 1). The 

emergence of these resistant biotypes demonstrates the continued need to utilize diversified weed 

management practices, including the need for additional herbicide modes-of-action that are 

effective in major crops. The WSSA reports: “Weed scientists know that the best defense 

against weed resistance is to proactively use a combination of agronomic practices, including the 

judicious use of herbicides with alternative modes-of-action either concurrently or sequentially” 

(WSSA 2010). Refer to Appendix B of the November 2013 Petitioner’s Environmental Report 

for DTS and DGT Cotton (petitions 10-188-01p and 12-185-01p_a1) (Monsanto 2013b) for 

additional details on herbicide resistance. 

Importantly, however, evidence to date indicates that resistance to dicamba and auxins is a lower 

probability than many other herbicides. Indeed, there is no evidence of cross-resistance to other 

herbicide modes-of-action after more than 50 years of use of any auxinic herbicide and where 

resistance mechanisms for dicamba have been studied, there is little to no evidence for the type 

of mechanism that would suggest the possibility for cross-resistance to other herbicides modesof-action. Thus, leading experts on resistance to auxinic herbicides, and in particular dicamba 

and 2,4-D, are clear in their judgment that the evolution of resistance to dicamba is not likely to 

result in cross-resistance to herbicides with other modes-of-action and therefore the risk of 

dicamba resistance is no greater than the risk of resistance to most other herbicides. 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 9 of 53 

Table 1 – Multiple Resistant Broadleaf Weeds in Soybean and Cotton Production Areas1

Weed Species 

Biotypes with Known Resistant 

Soybean Production2 Cotton Production3

Herbicide MOAs Classes5 Herbicide MOAs Classes5

Waterhemp ALS / PS II ALS/PPO 

 ALS / PPO ALS/PPO/GLY 

 ALS / GLY 

 ALS / PS II / PPO 

 ALS / PPO / GLY 

 ALS / PS II / HPPD 

 ALS / PS II / HPPD / GLY 

Palmer amaranth ALS / GLY ALS/GLY 

 ALS / PS II / HPPD 

Marestail ALS / GLY GLY/Bipyridilium 

 GLY / Bipyridilium 

Ragweed spp. ALS / PPO 

 ALS / GLY 

Redroot pigweed ALS / PS II 

Kochia4 ALS / PS II 1

 Source: (Heap 2014c) 

2 If weed populations with resistance to multiple herbicide modes-of-action are reported in corn or cropland in 

states where soybean is grown, these populations were also included. 3 If weed populations with resistance to multiple herbicide modes-of-action are reported in soybean or cropland in 

states where cotton is grown, these populations were also included. 4 Populations with resistance to dicamba exist; however, no known populations with resistance to both dicamba and 

glyphosate exist. 5

 ALS (acetolactate synthase inhibitors), PS II (photosystem II inhibitors), PPO (protoporhpyrinogen oxidase 

inhibitors), GLY (glycines), HPPD (p-hydroxyphenyl pyruvate dioxygenase), Bipyridilium (paraquat) 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 10 of 53 

Benefits of DT Soybean and DGT Cotton for Weed Control and Resistance

Management

New herbicide options are needed in soybean and cotton in order to manage present and future 

growth of resistant weed species, including glyphosate resistant weeds, and species with 

resistance to multiple herbicides. Today in U.S. soybean and cotton areas the weed species of 

most concern are broadleaf species, specifically summer annual species such as those in the 

Amarathus and Ambrosia genus. Dicamba is an effective herbicide on these and other targeted 

summer broadleaf species, is compatible and complementary to glyphosate and will be an 

essential tool to assist soybean and cotton growers to effectively manage weeds and weed 

resistance in general. The ability to use dicamba on DT soybean and DGT cotton will offer 

farmers an additional option for management of broadleaf weeds at a time when current 

herbicide options are becoming more limited because of the spread of biotypes with resistance to 

multiple herbicides and multiple herbicide modes of action. Dicamba will almost exclusively be 

used in combination with other herbicides including glyphosate, glufosinate and other soil 

residual and postemergence active herbicides currently labeled for use in either soybean or 

cotton. In soybean, there are three basic weed management systems today; a diversified system 

including multiple herbicides with different modes of action, herbicides combined with nonherbicide management options, and, to a lesser degree, systems that still rely solely on 

glyphosate. In cotton, most farmers in the southeast, mid-south and Texas regions are using 

diversified weed management programs today, whereas cotton farmers in the western states are 

primarily relying only on glyphosate. Dicamba will be incorporated into these existing 

diversified weed management approaches in both soybean and cotton, but will replace in whole 

or part the use of some currently used non-glyphosate herbicides. Furthermore, it is anticipated 

that the ability to safely use dicamba over the top of soybean and cotton and the subsequent 

benefits (e.g., simplicity, flexibility, effectiveness) of using dicamba will encourage farmers 

currently relying solely on glyphosate to incorporate more diversity into their weed management 

programs. 

The net effects of dicamba use for weed control in soybean and cotton will be to: (1) further 

mitigate the potential for evolution of herbicide resistance to glyphosate, dicamba and other 

herbicides; (2) provide overall better weed control for herbicide resistant weeds such as Palmer 

amaranth and waterhemp, and hard-to-control weeds such as morningglory and wild buckwheat; 

(3) help to manage glyphosate-resistant weeds, therefore preserve and grow conservation tillage 

acres and its associated environmental benefits; (4) increase the adoption of proactive measures 

to mitigate the evolution and spread of herbicide resistant broadleaf populations11; and (5) 

                                                           

11 Grower adoption of recommended weed resistance management programs has increased in recent years, however 

inconvenience, difficulty or concerns associated with these programs (e.g., plant back intervals, rainfall and/or soil 

restrictions, crop safety concerns) have been a factor in adoption. Because of the compatibility and complementary 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 11 of 53 

displace, in part, some herbicides that have less benign human health and environment profiles 

compared to dicamba (e.g., paraquat). 

DT soybean and DGT cotton will be sold only in soybean and cotton varieties that also contain 

glyphosate-tolerance. Stacking DT soybean and/or DGT cotton with glyphosate-tolerant traits 

would enable use of a combination of different herbicide modes of action on these crops, an 

approach that is expected to manage existing hard-to-control and resistant weeds, and mitigate 

the potential for future development of herbicide-resistant weeds (Duke and Powles 2009). The 

use of dicamba for soybean, and dicamba and glufosinate for cotton, provides enhanced weed 

management options in soybean and cotton cultivation to control a broad spectrum of broadleaf 

weed species. These uses of dicamba and glufosinate also provide effective control of herbicide 

resistant broadleaf weeds that have arisen in certain areas of the U.S. and which are impacting 

both conventional and existing genetically engineered (GE) crops. Existing GE crops have 

provided enormous benefits to farmers in recent decades, including improved yields, lower costs, 

decreased emissions from farm equipment, increased use of conservation tillage and associated 

environmental benefits, and the ability to use herbicides with a more benign human health and 

environmental profile. These existing GE crops continue to offer these benefits, and the 

availability of new herbicide tools should be used to offset the development of more widespread 

selection of resistant weeds so that glyphosate continues to be an important weed management 

tool nationwide. Today, successful integration of DT soybean and DGT cotton can enhance 

weed management systems by providing additional in-crop herbicide modes-of-action, while 

fostering growers’ use of established production practices, reduced tillage systems, and the same 

planting and harvesting machinery. DT soybean and DGT cotton will also help growers maintain 

yield and quality to meet the growing need for food, feed and fiber, both domestically and for 

export markets. 

Equally important are the potential negative impacts may result if new herbicide tools such as 

DT soybean and DGT cotton are not available to U.S. growers: (1) the number of herbicide 

resistant weed species and the number of acres infested with resistant weed populations would be 

expected to grow, consequently, additional financial and environmental challenges are likely; 

and (2) important herbicide options may lose their effectiveness forcing growers to incorporate 

other less economical cultural practices. Many weed scientists have speculated that for certain 

herbicides and weed species (i.e., glufosinate or PPO herbicides such as flumioxizin and 

fomesafen in Amaranthus spp.) resistance will evolve and grow in the absence of new herbicide 

options (Tranel et al. 2010). Since these herbicides are currently major tools used to manage 

glyphosate and ALS resistant Amaranthus spp. in soybean and cotton, farmers will be forced to 

incorporate mechanical practices which will be less effective and result in a general reduction in 

yields, as well as loss of conservation tillage acres. 

                                                                                                                                                                                               

nature of dicamba with the glyphosate-tolerant cropping system, the reluctance of some farmers to implement 

recommended resistant management programs may be reduced.
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 12 of 53 

Dicamba Resistance: Potential		

The auxin herbicide group is the oldest class of herbicides and includes 2,4 D - the first herbicide 

commercialized in the U.S. in the late 1940’s. To date, globally there are only 29 species with 

confirmed resistance to auxins. Of these 29 species, there are five species globally with 

confirmed resistance to dicamba, including four species in the U.S. and Canada, and 17 species 

with confirmed resistance to 2,4-D in the U.S. (Heap 2014e). This is a relatively low incidence 

of resistance considering the length of time these products have been used and the volume of use 

in the U.S. and worldwide. This low level of resistance is most likely due to inherent 

physiological activity of auxins in plants and genetic factors, as well as how they are generally 

used in farm level weed management programs (i.e., they are often used in conjunction with 

other herbicide mode of actions). 

From a physiological and genetics perspective the potential for resistance to evolve to dicamba is 

considered low by leading academic experts. A full explanation of these factors was provided by 

Dr. Mithila Jugulam and J. Christopher Hall as presented in comments submitted on June 24, 

2013 to USDA during the DT soybean and DGT cotton EIS Notice of Intent comment period 

(See Appendix A). These authors also published a scientific paper in 2011 that provided a 

thorough review of what is known about auxin resistance (Mithila, et al. 2011). As presented 

and summarized there, the low rate of evolution of resistance to auxins is likely due to: (1) the 

rare presence of alleles imparting resistance; (2) a fitness penalty associated with resistant 

alleles; (3) the complex mode of action of these herbicides; (4) the mode of action in plants may 

be governed by multiple genes which in turn may mean multiple genes are needed for resistance; 

and (5) in some species, resistance may be conferred only by recessive genes. Dicamba, 2,4-D 

and most other auxins such as MCPA are commonly used in combinations with other herbicides 

either as mixtures or in sequences. For dicamba, this is demonstrated in the data provided in 

Table 2. Also, in use areas such as pastures and turf, non-chemical weed management activities 

such as mowing are also used in building diversified weed management programs and assists in 

retarding the selection and proliferation of auxin resistant biotypes. While resistance to dicamba 

and other auxins has evolved in some species, the evidence indicating a low potential for 

resistance to evolve does suggest that reasonable resistance management practices can be 

implemented to effectively mitigate or prevent widespread resistance from evolving. 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 13 of 53 

Table 2: Summary of Dicamba Use in U.S. Agricultural Practices 

U.S. Total 

2012 Treated Acres 

% 

Dicamba 

Only 

Total Dicamba 

(mixtures + alone) 

Dicamba 

Only 

Dicamba 

Mixtures 

Corn 11,919,841 441,945 11,477,896 4% 

Fallow 6,665,137 17,757 6,647,380 0.3% 

Winter Wheat 3,622,105 135,020 3,487,085 4% 

Pastureland 3,221,382 492,671 2,728,711 15% 

Spring Wheat 1,804,741 79,148 1,725,593 4% 

Sorghum 1,683,586 49,491 1,634,095 3% 

Cotton 1,455,312 79,093 1,376,219 5% 

Soybeans 1,055,926 3,215 1,052,711 0.3% 

Sugarcane 190,317 - - 0% 

Source: BASF Corporation market research 

Cross-resistance to other auxin herbicides and herbicides with different modes of action also 

needs to be considered. The best understood case of cross resistance between different 

herbicides with different modes of action involves metabolic resistance, specifically 

hydroxylation of cytochrome P450’s (Powles and Yu 2010). As presented by Drs. Jugulam and 

Hall in their comments to USDA, the relative potential of dicamba resistance to be a source of 

cross-resistance to herbicides with different modes of action is low based upon the research 

conducted to date. As they state, “Of the 5 species (with resistance to auxins) where metabolism 

has been studied, in only 1 species and herbicide combination (MCPA resistant hemp-nettle) has 

metabolism been suspected.” However, the potential for cross-resistance to other herbicides 

within the auxin group, particularly cross-resistance between dicamba and 2,4-D exists, and a 

few confirmed 2,4-D resistant biotypes have exhibited resistance to dicamba. However 

according to available research not all weed species or populations with resistance to 2,4-D are 

cross-resistant to dicamba and vice versa (Mithila et al. 2011). 

Impact of Dicamba Resistance			

As for any herbicide, there is always the potential for resistance to evolve as a function of its use. 

However, this potential can be reduced by farmer adoption of certain best management practices, 

foremost of which is to use herbicides in a diversified weed management program within a 

specific crop and/or across a crop rotation. With the approval of DT soybean and DGT cotton, 

the use of dicamba for weed control is expected to increase relative to uses in currently approved 

crops and farming systems. As such, the potential exists for new species to evolve resistance to 

dicamba. However, the probability of resistance developing depends on the weed management 

practices utilized in current dicamba crops and farming systems, as well as the practices that will 

be employed for the new uses of dicamba in DT soybean and DGT cotton. In evaluating the 

impact of dicamba resistance, should it arise, it is also important to evaluate the impact of 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 14 of 53 

resistance on current uses of dicamba. The following is an assessment of the risk of, and 

mitigation of the potential for, dicamba resistance in crops and farming systems where dicamba 

use is currently approved. 

Methods

For this analysis, BASF Corporation market research information was used to identify and 

characterize weed management practices in the major markets where dicamba is used today. The 

analysis was conducted by regions because dicamba use and weed management practices can 

vary across different regions of the U.S. States were divided into four regions and the states in 

each region were selected on the basis of where soybeans and cotton are primarily grown. The 

states assigned to each region are listed in Table 3. 

Table 3: Regional Classifications Used in Assessment 

Region States 

Plains1 North Dakota, South Dakota, Nebraska, Oklahoma, Kansas, Texas 

Delta (Midsouth)2 Mississippi, Arkansas, Louisiana, Tennessee 

Southeast3 North Carolina, South Carolina, Georgia, Alabama 

Midwest4 Iowa, Illinois, Indiana, Ohio, Minnesota, Wisconsin, Missouri, Michigan 

1 The Plains region above is included in Table II.B-2 U.S. Soybean Production by Region and State in 2012: Midwest and Plains 

Regions from the November 2013 Environmental Report. Cotton is not typically produced in this region, except for Oklahoma 

and Texas. 

2 The Mid-South region above is included in Table II.B-4 Common Weeds in Soybean Production: Southeast region and Table 

II.B-15 Common Weeds in Cotton Production in the Mid-South Region of the U.S. from the November 2013 Environmental 

Report. 

3 The Southeast region above is included in Table II.B-4 Common Weeds in Soybean Production: Southeast region and Table 

II.B-14 Common Weeds in Cotton Production in the Southeast Region of the U.S. from the November 2013 Environmental 

Report. 

4 The Midwest region above is included in Table II.B-3 Common Weeds in Soybean Production: Midwest Region from the 

November 2013 Environmental Report. Cotton is not typically produced in this region. 

Results and Discussion

Current Dicamba Uses and Identification of Highest Risk Areas

Dicamba herbicides are currently registered for use in asparagus, conservation reserve programs, 

corn, cotton, fallow croplands, general farmstead (non cropland), sorghum, grass grown for seed, 

hay, proso millet, pasture, rangeland, small grains, soybeans, sugarcane, and turf (BASF 

Corporation 2008). In each region, a subset of labeled crop uses was examined in a market 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 15 of 53 

research analysis, see Table 4. The analysis focused on these market segments because they 

represent the crop segments that could be impacted the most if resistance evolved due to the use 

of dicamba in DT soybean and DGT cotton. They also represent the highest volumes of dicamba 

use today. Some dicamba uses listed in the Clarity herbicide label were not considered relevant 

to this analysis and have been excluded as follows: (1) grass grown for seed and proso millet 

because crop production tends to be concentrated in the western U.S., which is outside the 

primary areas of soybean and cotton production; (2) turf uses because the weed targets are 

different; (3) asparagus because the crop acreage and use of dicamba is minor; and (4) 

conservation reserve programs and general farmstead because their weed targets and dicamba 

use patterns would be similar to uses in fallow and pasture and rangeland. 

Dicamba is an effective broadleaf herbicide and is limited to preplant uses in broadleaf crops that 

lack crop safety12; in other crops, dicamba is used in-crop when there is adequate selectivity/crop 

safety. Dicamba is used in-crop in corn, wheat, grass pastures and sorghum. In soybeans and 

cotton, dicamba can be safely used prior to planting when established plant back intervals are 

observed. 

Table 4: Dicamba Use by Crop and Year 

Crop/Year 2006 2008 2010 2012 

 Dicamba Treated Acres 

Corn 8,080,614 8,113,801 6,459,632 11,919,844

Fallow 2,144,260 3,017,717 4,274,678 6,665,140

Wheat, Winter 2,348,897 3,742,572 2,577,953 3,622,102

Pastureland 1,454,649 1,218,179 2,604,944 3,221,382

Wheat, Spring 1,569,079 1,351,665 1,512,894 1,804,742

Sorghum (Milo) 550,795 1,114,162 955,997 1,683,584

Cotton 590,953 589,919 854,649 1,455,309

Soybeans 279,275 529,638 648,509 1,055,926

Sugarcane 198,042 177,089 225,295 190,317

Barley 108,393 211,067 101,158 47,144

Source: BASF Corporation Market Research 

Within the above defined geographical regions, the combined use of dicamba in currently labeled 

crops and farming systems (e.g., fallow) generally represents a low percentage of total planted 

acreage of these crops and farming systems (see Table 5). Only in the Plains states – where 

dicamba is a primary weed control tool in corn, fallow and sorghum – is dicamba used on more 

than 10% of the total production area across the crops and farming situations where dicamba is 

approved for use. (See Table 6 for detailed information on dicamba uses in each of the defined 

geographical regions.) The relatively low use of dicamba today across these regions indicates an 

overall low level of resistance selection pressure on the targeted weeds. 

                                                           

12 Injury can occur when broadleaf crops come in contact with dicamba. 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 16 of 53 

Table 5: Dicamba Treated Acres by Region 

Region/Year 2012 

Dicamba Treated Acres as % of 

Planted Area of Crops listed in 

Table 2 

Plains 14% 

Midsouth 9% 

Southeast 4% 

Midwest 3% 

Monsanto proprietary grower survey data from 2013 

Dicamba Weed Targets

The primary weed targets for dicamba as identified by farmers in the market research surveys for 

each crop/farming system are listed in Table 6. Based on the known weed control spectrum of 

dicamba, growers applied dicamba to primarily target annual, biennial, and perennial broadleaf 

weeds, but also targeted a mixture of warm season (summer germinating/growing) and cool 

season (fall, winter, and spring germinating/growing) species. Where the weed spectrum is 

dominated by cool season species, dicamba applications would most likely be in the fall or 

spring. Conversely, if the weed spectrum is dominated by warm season species, the applications 

would be in the late spring and summer. Information on current application timing of dicamba in 

the various labeled crops is summarized in Table 7. 

Characterizing the timing of dicamba applications and associated weed targets is important to 

understand the intensity of selection pressure on specific species, particularly those that are the 

target of in-crop applications of dicamba in DT soybean and DGT cotton. In DT soybean and 

DGT cotton, a summer spectrum (e.g., warm season) of broadleaf weeds will be the primary 

weed targets. Preplant / preemergence uses of dicamba prior to planting of DT soybean or DGT 

cotton will be similar to current uses of dicamba in soybeans and cotton today except for the 

elimination of planting intervals that will allow dicamba to be applied before, at and after 

planting. The major warm season weeds that are the target of dicamba applications in current 

crop uses are listed in Table 8 through Table 11. 

Per the information found in Tables 6 and Appendix B, there will be some overlap of dicamba 

targeted weed spectrums between the new uses in DT soybean and DGT cotton and other 

crops/farming systems where dicamba is currently used, but in many cases there is no overlap of 

weed species. Note: Appendix B contains a breakdown of common weeds in soybean and 

cotton by region. In particular, there will be little overlap in the cool season and perennial 

species that are the focus of dicamba applications today in wheat and pastureland with weed 

targets for the new uses in DT soybean and DGT cotton. Species common to both current and 

new uses of dicamba are the warm season species Amaranthus spp. (i.e., Palmer amaranth, 

waterhemp, redroot pigweed), Ambrosia spp. (i.e., ragweed), morningglory, wild buckwheat, 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 17 of 53 

kochia, cocklebur, and lambsquarters. Another important target weed common to current and 

new uses of dicamba is the cool season species, Conyza spp. (i.e., horseweed or marestail). 

Therefore, with this overlap, a key to managing the potential risk for dicamba resistance in these 

species due to combined selection pressure across current and new uses is the diversified weed 

management systems in which dicamba is currently used and expected to be used in DT soybean 

and DGT cotton. Diversified weed management programs are the key to managing increased 

selection pressure. Weed management system recommendations in DT soybean and DGT cotton, 

as defined in Monsanto‘s submissions to USDA, will include a combination of herbicides with 

different modes of action in addition to dicamba and glyphosate, and glufosinate in the case of 

cotton. The weed management systems in which dicamba is used in currently approved crops 

and farming systems are defined in the next section. 

Weed Management Systems for Current Dicamba Uses

The grower market research data used in this analysis indicates that dicamba is primarily used 

today in combination with other herbicides with overlapping activity on dicamba targeted weeds. 

This is because dicamba expands or complements the broadleaf activity of a wide range of 

herbicides. According to market research data (see Table 2) the application of dicamba in the 

absence of another herbicide is at or below 5% of the total dicamba treated acres in each 

crop/farming system except in pastureland, where approximately 15% of dicamba‘s applications 

are made in the absence of other herbicides. This provides additional evidence that dicamba is 

generally used in a diversified weed management program with other herbicides and as such will 

significantly mitigate the evolution of dicamba resistance as a function of dicamba use in current 

labeled crops and in DT soybean and DGT cotton, even though there is some overlap of weed 

species between soybean and cotton, and other crops where dicamba can be used. Additionally 

this will significantly mitigate the potential for evolution of dicamba resistance in possible crop 

rotation systems where dicamba could be used in each rotation. 

Herbicide Options to Control Weeds in Current Dicamba Crop Uses

Should resistance to dicamba evolve over time to any of the targeted weed species due to any use 

of dicamba, there will be multiple herbicide options available in the crops and farming systems 

where dicamba is currently being used. A listing of some of these herbicide options is presented 

in Table 8 through Table 11. It is important to note that there are multiple herbicide options and 

multiple modes of action available across the dicamba-labeled crops. Therefore, even if 

populations where resistance to more than one herbicide mode of action is present, there is likely 

to be an alternative herbicide available for use and therefore minimal impact on production and 

herbicide uses in traditional dicamba use areas would be expected. 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 18 of 53 

Scope and Impact of Existing Dicamba Resistant Species

Dicamba-resistant weeds account for 1% of resistant biotypes today (Heap 2014f). To date, 

there are four species with known resistant biotypes to dicamba in the U.S./Canada after over 40 

years of use: common hempnettle (Galeopsis tetrahit), wild mustard (Sinapis arvensis), kochia 

(Kochia scoparia), and prickly lettuce (Lactuca serriola L.) (Heap 2014f). 

The dicamba resistant biotypes identified in Canada include common hempnettle and wild 

mustard. Common hempnettle biotypes identified in barley, cereals, cropland, and wheat in 

1998 demonstrated resistance to dicamba, fluroxypyr, and MCPA (Heap 2014h). Hempnettle is 

an annual weed most common in the northern plains of the U.S. and Canada, where it is 

generally a target for control in small grains. It is not a common or problematic weed species in 

soybean or cotton production (See Tables II.B.3 -5 and II.B.14 -17 in the November 2013 

Environmental Report). 

Wild mustard biotypes with resistance to 2,4-D, dicamba, dichlorprop, MCPA, mecoprop, and 

picloram were identified in Canada in 1990 in barley, cropland and wheat (Heap 2014a). Wild 

mustard is a common cool season weed in many areas of the U.S. It is most often a weed target 

in no-till situations at the early burndown application before planting crops such as soybeans or 

cotton. Wild mustard has not been identified as a major weed in soybean and cotton production 

(See Tables II.B.3 -5 and II.B.14 -17 in the November 2013 Environmental Report). 

Only kochia and prickly lettuce dicamba resistant biotypes have been identified in the U.S. 

Dicamba resistance kochia has been confirmed in ND and MT in wheat (1995), ID on roadsides 

(1997), and NE in corn (2010) (Heap 2014b). Kochia is not a common or problematic weed 

species in most soybean and cotton producing areas. However, kochia is a problematic weed in 

western sections of Kansas and Nebraska where some soybean is produced. (See Tables II.B.2-4 

and Tables II.B.14-17 in the November 2013 Environmental Report). Kochia can also be found 

in the north Texas cotton growing areas. Additional herbicide options such as glyphosate, 

glufosinate, pendimethalin, clomazone, paraquat, fumioxazin, and metribuzin are some of the 

options available to use in place of dicamba to control dicamba resistant kochia in these areas. 

While Kochia populations have also been identified with glyphosate, PSII (e.g. atrazine, 

metribuzin) and ALS (e.g. imazethapyr, thifensulfuron) resistance, not all populations are 

resistant to these herbicides and they remain effective in many situations. 

Prickly lettuce with 2,4-D resistance and cross-resistance to MCPA and dicamba was identified 

in Washington in 2007. Prickly lettuce is an annual or biennial that is found throughout the U.S. 

It is not commonly a targeted weed for control in soybeans or cotton since it is primarily found in 

cereals, orchards, pastures, roadsides, railroads, and waste areas (See Tables II.B.3 -5 and 

II.B.14-17 of the November 2013 Petitioner’s Environmental Report (Monsanto 2013a)). 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 19 of 53 

The persistence of herbicide resistant biotypes is in part related to the presence or absence of a 

fitness penalty that may be associated with the resistant alleles. A fitness penalty is characterized 

as resistant biotypes being less competitive with non-resistant biotypes of the same species and 

therefore less persistent in the environment. As reviewed by Mithila et al. (2011), there is 

evidence of reduced fitness in some auxin resistant biotypes. The presence of a fitness penalty 

has been suggested to be a reason why auxin resistant biotypes do not appear to persist in the 

environment. 

In summary, of the species with known resistance to dicamba today, the primary species of 

concern relative to the new uses of dicamba in DT soybean and DGT cotton is kochia: its 

geographical distribution overlaps with some of the soybean and cotton production areas, it is a 

summer annual, and it would be an in-crop weed target. The key to mitigating dicamba 

resistance is implementation of a diverse weed control program that includes redundant, effective 

control measures, and scouting to eliminate weed escapes, as noted above, however, there are 

other herbicide options to manage any dicamba-resistant populations should they arise in both 

soybeans and cotton. 

Weed Resistance Management Stewardship

To support the introduction of varieties containing DT soybean and DGT cotton, Monsanto will 

use multiple methods to distribute technical and stewardship information to growers, academics 

and grower advisors regarding the use of the product as part of a diversified weed management 

system. Growers who purchase Monsanto varieties containing DT soybean or DGT cotton sign a 

limited use license known as the Monsanto Technology Stewardship Agreement (MTSA). The 

MTSA obligates growers to comply with certain requirements, including the Monsanto 

Technology Use Guide (TUG). The TUG will set forth the requirements and best practices for 

the cultivation of DT soybean and DGT cotton including recommendations on weed resistance 

management practices. Monsanto provides up to date information and resources to assist 

growers in implementing weed resistance management strategies through its weed management 

website13 and mobile applications. 

Conclusions

With the approval of DT soybean and DGT cotton, there will be an increase in dicamba use and 

therefore some possibility of an increased potential for resistance to evolve. However, this risk 

will be greatly mitigated by the fact that dicamba is used in diversified weed management 

systems today, in current markets, and will likewise be used in diversified weed management 

systems when dicamba is approved for use in DT soybean and DGT cotton. Monsanto, BASF, 

                                                           

13 http://www.monsanto.com/weedmanagement/Pages/field-management-guidelines.aspx
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 20 of 53 

the Weed Science Society of America (WSSA), academics and extension service agents have 

made significant progress in changing grower behavior to adopt diversified weed management 

practices. On-going and planned educational efforts will continue to stress the importance of 

using dicamba in a diversified program, therefore adoption of diversified weed management 

practices is expected to continue. Moreover, in many instances weeds that are targeted by a 

dicamba application (i.e., Amaranthus sp. such as Palmer amaranth and waterhemp) require the 

use of multiple weed control practices in order to meet grower weed control expectations, this 

provides additional assurances that dicamba will be used in a diversified program. 

When a herbicide is used in a diversified weed management system that includes other 

herbicides with overlapping spectrum of control and different modes-of-action, it can be used 

repeatedly within a cropping season and across multiple seasons without significantly impacting 

the risk of resistance (Beckie and Reboud 2009). Therefore, the potential for development of 

dicamba resistance can be significantly mitigated when dicamba-tolerant crops are rotated with 

each other and/or with crops where dicamba is currently approved. There is strong scientific 

justification for this conclusion, as indicated by theories of resistance evolution and management 

supported by field and resistance modeling studies (Beckie and Reboud 2009; Neve, et al. 2011) 

and the weed science academic community.14,15,16

However, the possibility of gradual evolution of resistance (through selection) to any herbicide 

cannot be completely eliminated if the benefits of the use are to be realized. Therefore, an 

understanding of the impact of this potential resistance and ways to mitigate the impact are an 

important part of weed resistance risk assessment. In this case, options for managing key 

dicamba targeted weeds in each of the major crops and farming systems where dicamba is used 

today was evaluated. This analysis supports that the availability of multiple herbicide options 

with different modes of action will mitigate any potential future impacts of dicamba resistance. 

Likewise, there are multiple options to manage dicamba resistant populations of kochia should 

this become an issue in some of the western soybean and cotton growing regions where DT 

soybeans and DGT cotton may be grown. In addition, the potential for development of 

additional dicamba resistant populations will be mitigated through the use of diversified weed 

management programs, which include the use of multiple herbicides, in DT soybeans and DGT 

cotton. The availability of options to manage dicamba resistant populations, plus the indications 

that resistant biotypes are not as competitive as non-resistant biotypes, both point to low impact 

of resistant populations on farming operations and the environment. 

                                                           

14 APHIS-2013-0043-0019, available at http://www.regulations.gov/#!documentDetail;D=APHIS-2013-0043-0019

15 APHIS-2013-0043-0027, available at http://www.regulations.gov/#!documentDetail;D=APHIS-2013-0043-0027

16 APHIS-2013-0043-0054 available at http://www.regulations.gov/#!documentDetail;D=APHIS-2013-0043-0054
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 21 of 53 

Lastly, leading experts on resistance to auxinic herbicides, and in particular dicamba and 2,4-D, 

are clear in their judgment that the evolution of resistance to dicamba is not likely to result in 

cross-resistance to herbicides with other modes of action and therefore the risk of dicamba 

resistance is no greater than the risk of resistance to most other herbicides. In fact, evidence to 

date indicates that resistance to dicamba and auxins is a lower probability than many other 

herbicides. The main reasons for this judgment are that definitive mechanisms for resistance to 

auxinic herbicides have yet to be defined; there is no evidence of cross-resistance to other 

herbicide modes of action after more than 50 years of use of any auxinic herbicide and where 

resistance mechanisms for dicamba have been studied, there is little to no evidence for the type 

of mechanism that would suggest the possibility for cross-resistance to other herbicides modes of 

action. 

In closing, the keys to minimizing the impact of resistance to any herbicide are first to mitigate 

the risk of resistance evolving, and second, to have economical and practical options for 

managing resistance should it evolve. In the case of the proposed new uses of dicamba in DT 

soybean and DGT cotton, there is ample evidence that the impact of dicamba resistance is 

minimal and manageable and does not rise to a level of concern that would adversely impact the 

environment nor be of a significant economic burden to producers. In the unlikely case that 

broadleaf weeds were to evolve or develop resistance to dicamba over time, existing cultivation 

and alternative herbicide tools (see Section II.B.2.d in the November 2013 Environmental Report 

(Monsanto 2013a)) for a description of alternative herbicides) would remain potential options to 

provide effective control. Additionally, any potential risks are far outweighed by the benefits 

that can be derived from dicamba use to mitigate resistance to other herbicides in an economical 

fashion. 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 6. Dicamba Weed Targets 1

Midwest Region Crop 

Dicamba Treated Acres 

Total Crop Acres 

Dicamba Treated as % of Total Dicamba Weed Targets (listed in order of treated acr

Corn 3,403,861 56,350,032 6% lambsquarters giant ragweed velvetleaf red pigweed waterhemp cocklebur raCotton 210,863 375,002 56% marestail red pigweed chickweed henbit Palmer 

amaranth 

Pastureland 48,788 19,222,408 0% musk thistle bull thistle ragweed Canada thistle Soybeans 85,474 43,690,011 0% marestail waterhemp sweet 

clover 

Wheat, Spring 

10,000 1,400,016 1% red pigweed wild mustard 

Wheat, Winter 

33,543 3,225,000 1% chickweed velvetleaf giant 

ragweed 

Total for Region 3,792,529 124,262,469 3% Southeast Region Corn 324,511 1,795,003 18% morningglory red pigweed giant ragweed marestail lambs- quarter bur- cucumber cCotton 73,815 2,469,994 3% marestail evening 

primrose 

Pastureland 121,618 6,734,886 2% wild carrot Canada thistle bitter sneezeweed red pigweed dandelion dog fennel Soybeans 52,800 2,610,001 2% marestail smartweed Total for Region 572,744 4% 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 6 (continued). Dicamba Weed Targets 1

Delta (Midsouth) Region Crop 

Dicamba Treated Acres 

Total Crop Acres 

Dicamba Treated as % of Total Dicamba Weed Targets (listed in order of treated acr

Cotton 670,995 1,769,995 38% marestail red pigweed curly dock ragwort evening 

primrose 

hebit 

Soybeans 670,148 7,732,424 9% marestail dock ragweed redroot 

pig 

Morningglory sicklepod P

a

Corn 452,712 2,861,058 16% marestail Palmer 

amaranth 

redroot pig morningglory hebit dock 

Sugarcane 186,911 425,003 44% morningglory redroot pigweed clover Pastureland 175,758 10,065,529 2% thistle red pigweed blue vervain marigold dogfennel croton C

th

Wheat, Winter 

64,992 888,010 7% 

Sorghum (Milo) 

22,578 269,999 8% 

Fallow 630 91,858 1% Total for Region 

2,244,724 24,103,876 9% 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 6 (continued). Dicamba Weed Targets 1Plains Region Crop 

Dicamba Treated Acres 

Total Crop Acres 

Dicamba Treated as % of Total Dicamba Weed Targets (listed in order of treated ac

Barley 12,199 1,174,988 1% Corn 6,234,992 26,270,008 24% kochia redroot 

pigweed 

waterhemp Russian 

thistle 

lambsquarters Palmer amaranth 

Cotton 499,636 7,197,966 7% marestail Russian 

thistle 

wild mustard ironweed kochia henbit 

Fallow 3,391,068 6,798,789 50% kochia Russian 

thistle 

redroot pigweed 

field bindweed 

puncture vine 

wild buckwheat 

Pastureland 2,539,862 32,306,093 8% ragweed broomweed marshelder St. 

johnswort 

milkweed sunflower 

Sorghum (Milo) 

1,556,474 5,404,998 29% kochia redroot 

pigweed 

Russian thistle 

filed bindweed 

mild mustard 

tumple pigweed 

Soybeans 244,253 18,309,988 1% marestail kochia red pigweed henbit waterhemp pennycress Wheat, Spring 

1,127,246 8,108,004 14% kochia Canada 

thistle 

buckwheat field 

bindweed 

Russian thistle 

ragweed 

Wheat, Winter 

2,688,190 24,299,994 11% kochia redroot 

pigweed 

Russian thistle 

yellow mustard 

wild mustard field 

bindweed 

Total for Region 18,293,920 129,870,828 14% 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 25 of 53 

Table 7. Timing of Dicamba Applications for Current Crop Uses1

Crop and Application Timing 

Sum of Total 

Area Treated 

Weed Spectrum of primary 

application timing 

Corn 

At Planting 104,159 

Before Crop Emergence 638,605 

Early Post (Herbicides) 672,194 

Last Fall 446,739 

Late Post (Herbicides) 7,986,902 warm season 

Prior to Planting 2,071,242 cool season 

Corn Total* 11,919,841 

Cotton 

Last Fall 161,528 

Prior to Planting 1,293,784 warm and cool season 

Cotton Tota*l 1,455,312 

Soybean 

Last Fall 70,909 

Late Post (Herbicides) 

Prior to Planting 985,017 warm and cool season 

Soybeans Total* 1,055,926 

Sorghum (Milo) 

At Planting 37,631 

Before Crop Emergence 113,617 

Early Post (Herbicides) 22,094 

Last Fall 593,529 warm season 

Late Post (Herbicides) 148,849 

Prior to Planting 767,866 warm season 

Sorghum (Milo) Total* 1,683,586 

Sugarcane 

At Planting 1,116 

Before Crop Emergence 

Early Post (Herbicides) 7,958 

Last Fall 8,658 

Late Post (Herbicides) 94,344 warm season 

Prior to Planting 78,241 warm season 

Sugarcane Total* 190,317 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 26 of 53 

Table 7 (continued). Timing of Dicamba Applications for Current Crop Uses1

Crop and Application Timing 

Sum of Total 

Area Treated 

Weed Spectrum of primary 

application timing 

Barley 

Before Crop Emergence 239 

Early Post (Herbicides) 

Last Fall 4,764 

Late Post (Herbicides) 19,055 warm season 

Prior to Planting 23,086 cool season 

Barley Total* 47,144 

Wheat, Spring 

At Planting 26,401 

Before Crop Emergence 55,983 

Early Post (Herbicides) 2,499 

Last Fall 448,317 cool season 

Late Post (Herbicides) 631,465 warm season 

Prior to Planting 640,076 cool season 

Wheat, Spring Total* 1,804,741 

Wheat, Winter 

At Planting 6,838 

Before Crop Emergence 12,127 

Early Post (Herbicides) 

Last Fall 1,176,545 warm and cool season 

Late Post (Herbicides) 2,426,595 warm season 

Wheat, Winter Total* 3,622,105 

Fallow 

Last Fall 855,875 

This Year (Pasture, Fallow) 5,809,262 warm and cool season 

Fallow Total* 6,665,137 

Pastureland 

Last Fall 72,524 

This Year (Pasture, Fallow) 3,148,858 warm and cool season 

Pastureland Total* 3,221,382 

1 2012 BASF Market Research Data 

* Individual crop totals vary slightly from the total dicamba values shown in Table 2 due to rounding of the 

individual values for each application timing prior to summing all application timing acres for each crop.
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 8. Herbicide Options to Control Primary Weed Targets in Midwest Region (IA, IL, IN, OH, MN, WI, MO, M

Cotton 

Marestail3 Pigweed, 

redroot3

Chickweed3 Henbit3 Palmer 

amaranth3

 glufosinate diuron glyphosate glyphosate diuron  prometryn fluometuron paraquat oxyflurorfen fluometuron  metolachlor glufosinate paraquat metolachlor  fomesafen prometryn prometryn fomesafen 

Number herbicide MOA available 

2 4 4 4 3 

Corn 

Lambsquarters

1

Giant ragweed1

Velvetleaf1 Pigweed, 

redroot1

Waterhemp1 Cocklebur1 Ragweed, 

common1

 acetochlor atrazine atrazine acetochlor acetochlor atrazine acetolchlor  atrazine mesotrione isoxaflutole atrazine atrazine mesotrione Atrazine  mesotrione saflufenacil bentazon isoxaflutole isoxflutole saflufenacil saflufenacil  saflufenacil tembotrione halosulfuron mesotrione mesotrione tembotrione tembotrione  tembotrione mesotrione tembotrione tembotrione bentazon bentazon Number herbicide MOA available 

4 3 5 4 4 4 5 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 8 (continued). Herbicide Options to Control Primary Weed Targets in Midwest Region (IA, IL, IN, OH, MN, WI, MO, Soybean 

Marestail1 Waterhemp1

Sweet clover2

 saflufenacil + 

glufosinate 

metolachlor saflufenacil + 

glyphosate 

 metribuzin + 

glufosinate 

sulfentrazone saflufenacil 

 chlorimuron + 

glyphosate 

flumioxazin glyphosate + 

fumioxazin 

 fomesafen  lactofen Number herbicide MOA available 

5 2 2 

Spring Wheat  Pigweed, 

redroot1

Wild mustard1

carfentrazone prosulfuron sulfosulfuron sulfosulfuron florasulam florasulam prosulfuron pyroxsulam 

Number herbicide MOA available 

2 1 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 8 (continued). Herbicide Options to Control Primary Weed Targets in Midwest Region (IA, IL, IN, OH, MN, WI, MO, Winter Wheat  Chickweed1 Velvetleaf4 Giant ragweed1

propoxycarbazone carfentrazone prosulfuron florasulam prosulfuron florasulam prosulfuron pyroxsulam 

Number herbicide MOA available 

1 2 1 

Pastureland 

Thistle, musk5 Thistle, bull3,5 Ragweed6 Thistle, canada5metsulfuron metsulfuron5 metsulfuron metsulfuron  chlorsulfuron3

metsulfuron + chlorsulfuron 

Number herbicide MOA available 

1 1 1 1 

*Source for weed targets was Monsanto proprietary grower survey data from 2012. Weeds listed in descending order according to acreAlternative herbicides actives were rated 7-8 and above (good) for control of targeted weed.1 Loux, et al. 2013 2 University of Nebraska-Lincoln 2013 3 Mississippi State University 2013 4 University of Missouri 2013 5 University of Arkansas 2013 6 Penn State University 2013 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 9. Herbicide Options to Control Primary Weed Targets in Southeast Region (NC, SC, GA, AL)* 

Cotton 

Marestail5,6 Evening 

primrose5

 paraquat + diuron5 tribenuron + 

thifensulfuron 

 glufosinate6 paraquat  prometryn6 prometryn  glufosinate 

Number herbicide MOA available 

4 4 

Corn  Morningglory1 Pigweed, 

redroot1 

Giant ragweed2 Marestail3 Lambsquarters1 Burcucumber 1 

 atrazine acetochlor atazine mesotrione + 

atrazine 

atrazine atrazine 

 flumetsulam atrazine mesotrione glufosinate flumetsulam primsulfuron  mesotrione flumetsulam saflufenacil tembotrione + 

atrazine 

mesotrione paraquat 

 foramsulfuron mesotrione tembotrione topramezone + 

atrazine 

carfentrazone foramsulfuron 

Number herbicide MOA available 

4 4 4 3 4 4 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 9 (continued). Herbicide Options to Control Primary Weed Targets in Southeast Region (NC, SC, GA, AL)*

Soybean  Marestail4 Smartweed4 paraquat + 

metribuzin 

metribuzin 

 glufosinate clomazone  bentazon  lactofen Number herbicide MOA available 

3 4 

Pastureland 

Wild carrot Thistle, 

canada7

Bitter sneezeweed7

Thistles7 Pigweed, 

redroot7

Dandelion7 Dogfennel7 

 metsulfuron + 

chlorsulfuron 

metsulfuron metsulfuron + 

chlorsulfuron 

flumioxazin flumioxazin metsulfuron 

+ chlorsulfuron 

 metribuzin tebuthiuron metribuzin metsulfuron metsulfuron tebuthiuron  hexazinone metsulfuron + 

chlorsulfuron 

hexazinone metribuzin tebuthiuron 

 hexazinone hexazinone 

Number herbicide MOA available 

 2 2 2 3 4 2 

*Source for weed targets was Monsanto proprietary grower survey data from 2012. Weeds listed in descending order according to acre1 University of Georgia 2013c 2 Loux et al. 2013 3 University of Tennessee 2013 4 University of Georgia 2013a 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

5 University of Georgia 2013b 6 Mississippi State University 2013 7 McCullough 2008 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 10. Herbicide Options to Control Primary Weed Targets in Delta Region (MS, AR, LA, TN)* 

Cotton 

Marestail1 Pigweed, 

redroot1

Dock, curly1 Ragwort, tansy Evening 

primrose1

Henbit1

 glufosinate diuron tribenuron + 

thifensulfuron 

 tribenuron + 

thifensulfuron 

tribenuron + thifensulfuron 

 prometryn fluometuron oxyflurorfen paraquat glyphosate  metolachlor paraquat prometryn paraquat  glufosinate prometryn glufosinate prometryn  pendimethalin Number herbicide MOA available 

2 4 4 4 4 

Corn 

Marestail2 Palmer 

amaranth1

Pigweed, redroot1

Morningglory1 Henbit3 Dock3

 mesotrione + 

atrazine 

atrazine atrazine atrazine glyphosate glyphosate 

 glufosinate acetochlor acetochlor simazine paraquat glyphosate + 

flumioxazin 

 tembotirone + 

atrazine 

saflufenacil saflufenacil pyroxasulfone glyphosate + 

flumioxazin 

 topramezone + 

atrazine 

mesotrione mesotrione mesotrione 

 glyphosate Number herbicide MOA available 

3 4 4 4 3 2 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 10 (continued). Herbicide Options to Control Primary Weed Targets in Delta Region (MS, AR, LA, TN)* Soybean  Marestail3 Dock, sour1,3 Ragweed1 Pigweed, 

redroot1

Morningglory1 Sicklepod1 

 metribuzin + 

chlorimuron 

tribenuron + thifensulfuron1

metribuzin dimethenamid imazaquin fumioxazin 

 flumioxazin glyphosate + 

oxyflurorfen1

paraquat fomesafen fumioxazin metribuzin 

 metribuzin glyphosate + 

fumioxazin3

fomesafen metribuzin chlorimuron chlorimuron 

 chloransulam fumioxazin pendimethalin metribuzin fomesafen  chlorimuron chlorimuron glyphosate chloransulam Number herbicide MOA available 

3 3 4 5 4 3 

Sugarcane  Morningglory5,6 Pigweed, 

redroot5,6

Clover5

atrazine atrazine atrazine flumioxazin flumioxazin flumioxazin sulfentrazone sulfentrazone sulfentrazone metribuzin metribuzin metribuzin 

Number herbicide MOA available 

2 2 2 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 10 (continued). Herbicide Options to Control Primary Weed Targets in Delta Region (MS, AR, LA, TN)* 

Pastureland  Thistle3 Pigweed, 

redroot3

Ragweed3 Vervain, blue Marigold, dwarf Dogfennel3

metsulfuron + chlorsulfuron 

metsulfuron + chlorsulfuron 

metsulfuron + chlorsulfuron 

 metsulfuron 

chlorsulfur

chlorsulfuron chlorsulfuron metsulfuron tebuthiruro nicosulfuron + 

metsulfuron 

Number herbicide MOA available 

1 1 1 2 

*Source for weed targets was Monsanto proprietary grower survey data from 2012. Weeds listed in descending order according to acreAlternative herbicides actives were rated 7-8 and above (good) for control of targeted weed. 1 Mississippi State University 2013 2 University of Tennessee 20133 University of Arkansas 2014 4 University of Georgia 2013a 5 Louisiana State University 2013 6 Product Labels on CDMS website [http://www.cdms.net/LabelsMsds/LMDefault.aspx?t=]
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 11. Herbicide Options to Control Primary Weed Targets in Plains Region (ND, SD, NE, KS, OK, TX)* 

Cotton 

Marestail Thistle, Russian Mustard, wild Ironweed Kochia Henbit 

       

Number herbicide MOA available 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 11 (continued). Herbicide Options to Control Primary Weed Targets in Plains Region (ND, SD, NE, KS, OK

Corn  Kochia1 Pigweed, 

redroot1

Waterhemp1 Thistle, 

Russian1

Lambsquarters

1

Palmer amaranth1 

Buckwheat, wild2 

atrazine atrazine atrazine atrazine atrazine atrazine atrazine isoxaflutole isoxaflutole isoxaflutole isoxaflutole isoxaflutole isoxaflutole saflufenacil mesotrione mesotrione mesotrione mesotrione mesotrione mesotrione glyphosate saflufenacil saflufenacil saflufenacil saflufenacil saflufenacil saflufenacil glufosinate primsulfuron tembotrione tembotrione tembotrione acetochlor tembotrione bentazon 

 acetochlor acetochlor glyphosate carfentrazone acetochlor thiencarbazone 

+ tembotrione 

 tembotrione  glyphosate 

Number herbicide MOA available 

5 5 5 5 6 5 6 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 11 (continued). Herbicide Options to Control Primary Weed Targets in Plains Region (ND, SD, NE, KS, OK

Soybean  Marestail1 Kochia1 Pigweed, 

redroot1

Henbit1 Waterhemp1 Pennycress1 Mustard, wild3

paraquat pendimethalin metolachlor glyphosate metolachlor glyphosate carfentrazone saflufenacil clomazone metribuzin paraquat metribuzin paraquat metribuzin 

 flumioxazin/

glyphosate cloransulam flumioxazin imazethapyr flumioxazin imazethapyr bentazon 

 metribuzin/ 

chlorimuron metribuzin cloransulam imazaquin pendimethalin imazaquin acifluorfen cloransulam flumioxazin 

Pendimethalin saflufenacil fluthiacet saflufenacil chlorimuron 

 fluthiacet fluthiacet acifluorfen fomesafen 

Number herbicide MOA available 

5 5 5 4 4 4 4 

Spring Wheat  Kochia1,5 Thistles5 Buckwheat5 Bindweed, 

field 

 Thistle, russian1

Ragweed Moneywort M

W

Carfentrazone5 triasulfuron** Carfentra- zone no products found metsulfuron** trSaflufenacil

5 metsulfuron** triasulfuron triasulfuron** m

Imazamethabenz** chlorsansulam + metsulfuron metsulfuron prosulfuron** fltriasulfuron1 prosulfuron florasulam pr prosulfuron 

Number herbicide MOA available 

2 1 2 1 1 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 11 (continued). Herbicide Options to Control Primary Weed Targets in Plains Region (ND, SD, NE, KS, OK

Winter Wheat  Kochia1,5 Pigweed, 

redroot1

 Thistle, russian1

Mustard, yellow5 

Mustard, wild5

Bindweed, field 

Buckwheat, wild5 

carfentrazone metsulfuron metsulfuron** triasulfuron triasulfuron no products 

found 

carfentrazone 

saflufenacil triasulfuron triasulfuron** metsulfuron metsulfuron triasulfuron Imazamethabenz prosulfuron prosulfuron** florasulam florasulam metsulfuron triasulfuron1 prosulfuron prosulfuron florasulam  prosulfuron 

Number herbicide MOA available 

2 1 1 1 1 2 

Sorghum  Kochia1 Pigweed, 

redroot1

 Thistle, russian1

Bindweed, field6

Mustard, wild 

Pigweed, tumble1 

Palmer amaranth1

dimethenamid/atr 

atrazine atrazine quinclorac + 

atrazine 

 atrazine atrazine 

atrazine acetochlor/ 

atrazine 

acetochlor/ atrazine 

Carfenterazone* acetochlor + atrazine acetochlor+ atrazine 

saflufenacil carfentrazone saflufenacil carfentrazon

e 

carfentrazone 

 halosulfuron halosulfuron halosulfuron  saflufenacil saflufenacil saflufenacil 

Number herbicide MOA available 

3 4 3 1 4 4 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 

Table 11 (continued). Herbicide Options to Control Primary Weed Targets in Plains Region (ND, SD, NE, KS, OK

Pastureland  Ragweed4 Broomweed4 Marshelder St. Johnswort Milkweed Sunflower

metsulfuron metsulfuron metsulfurometsulfuron + chlorsulfuron 

metsulfuron + chlorsulfuron 

metsulfurochlorsulfu

mowing mowing 

Number herbicide MOA available 

1 1 1 

 Mustard, wild Cocklebur, 

spiny4

Thistle4

 metsulfuron metsulfuron 

metsulfuron + chlorsulfuron 

metsulfuron + chlorsulfuron 

 mowing mowing 

Number herbicide MOA available 

 1 1 

*Source for weed targets was Monsanto proprietary grower survey data from 2012. Weeds listed in descending order according to acreAlternative herbicides actives were rated 7-8 and above (good) for control of targeted weed except where identified with ** which inclu

control.

1 University of Nebraska-Lincoln 2013 

2 Moechnig, et al. 2011 3 Moechnig, et al. 2012a 4 Kansas State University 2014 5 Moechnig, et al. 2012b 6 Moechnig, et al. 2010 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 41 of 53 

Appendix A

Comments submitted by Dr. C. Hall and Dr. M. Jugulam to DT soybean MON 87708 and DGT 

Cotton MON 88701 Notice of Intent scoping comment period
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 42 of 53 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 43 of 53 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 44 of 53 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 45 of 53 

Appendix B

Common weeds in soybean and cotton production. 

This appendix contains information on the common weeds in soybean and cotton by region from 

the November 2013 Petitioner’s Environmental Report for DT Soybean MON 87708 and DGT 

Cotton MON 88701. 

Common Weeds in Soybean Production: Midwest Region 

Foxtail spp. (12)1 Ragweed, giant (3) Dandelion (1) 

Pigweed spp. (11) Shattercane (3) Johnson grass (1) 

Velvetleaf (11) Quackgrass (3) Milkweed, honeyvine (1) 

Lambsquarters (10) Buckwheat, wild (2) Nightshade, hairy (1) 

Cocklebur (9) Crabgrass spp. (2) Oats, wild (1) 

Ragweed, common (7) Kochia (2) Pokeweed, common (1) 

Smartweed spp. (6) Mustard, wild (2) Prickly sida (1) 

Morningglory spp. (5) Nightshade, Eastern black (2) Proso millet, wild (1) 

Sunflower, spp. (5) Palmer amaranth (2) Sandbur, field (1) 

Waterhemp spp. (5) Canada thistle (1) Venice mallow (1) 

Horseweed (marestail) (3) Chickweed (1) Volunteer cereal (1) 

Panicum, fall (3) Cupgrass, woolly (1) Volunteer corn (1) 

Dicamba is effective on weeds highlighted in bold. 1 Number provided in parenthesis is the number of states out of the thirteen total states in the Midwest 

region reporting each weed as a common weed. 

Sources: 

IL: University of Illinois (2002) and Aaron Hager, Extension Weed Specialist, University of Illinois - 

Personal Communication (2006). 

IN: 2003-2005 Statewide Purdue Horseweed Weed Survey, Special database query and personal 

communication (2006), Bill Johnson, Extension Weed Specialist, Purdue University. 

IA, MN, OH, WI: (WSSA 1992). 

KS: Dallas Petersen, Extension Weed Specialist, Kansas State - Personal communication (2006). 

KY, MO: (Webster, et al. 2005). 

MI: (Davis, et al. 2005). 

NE: Alex Martin, Extension Weed Specialist, University of Nebraska – Personal communication (2006).

ND: (Zollinger and Lym 2000). 

SD: Michael Moechnig, Extension Weed Specialist, South Dakota State University – Personal 

communication (2006). 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 46 of 53 

Common Weeds in Soybean Production: Southeast Region 

Morningglory spp. (8)1 Goosegrass (3) Cutleaf evening-primrose (1)

Crabgrass spp. (6) Johnsongrass (3) Groundcherry (1)

Prickly sida (6) Ragweed, common (3) Henbit (1)

Nutsedge spp. (6) Cocklebur (2) Lambsquarters (1)

Sicklepod (5) Florida beggarweed (2) Ragweed, giant (1)

Signalgrass, broadleaf (5) Hemp sesbania (2) Smartweed (1)

Palmer amaranth (4) Horseweed (marestail) (2) Spurge, nodding/hyssop (1)

Pigweed spp. (4) Texas millet (2) Spurge, Prostrate (1)

Barnyard grass (3) Browntop millet (1) Tropic croton (1)

Florida pusely (3) Copperleaf, hophorn (1)

Dicamba is effective on weeds highlighted in bold. 1 Number provided in parenthesis is the number of states out of the eight total states in the Southeast region 

reporting each weed as a common weed. 

Sources: 

AL, AR, GA, LA, NC, SC: (Webster, et al. 2009). 

MS, TN: (Webster et al. 2005). 

Common Weeds in Soybean Production: Eastern Coastal Region 

Foxtail spp. (6)1 Morningglory spp. (4) Dandelion (1)

Ragweed, common (6) Panicum, fall (4) Goosegrass (1)

Velvetleaf (6) Crabgrass spp. (3) Johnson grass (1)

Lambsquarters (5) Nutsedge spp. (3) Nightshade, Eastern black (1)

Pigweed spp. (5) Quackgrass (2) Prickly sida (1)

Cocklebur (4) Canada thistle (1) Shattercane (1)

Jimson weed (4) Burcucumber (1) Smartweed spp. (1)

Dicamba is effective on weeds highlighted in bold. 1 Number provided in parenthesis is the number of states out of the six total states in the Eastern Coastal 

region reporting each weed as a common weed. Data were not available for DE in soybean. 

Sources: 

DE, MD, NJ, PA: (WSSA 1992). 

NY: Russell Hahn, Extension Weed Specialist, Cornell University – Personal Communication (2006). 

VA: (Webster et al. 2009).
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 47 of 53 

Common Weeds In Cotton Production

Common weeds in Cotton Production in the Southeast Region of the U.S.1,2

Crabgrass spp. (6) 

Morningglory spp (6) 

Prickly sida (5) 

Florida pusley (4) 

Nutsedge spp. (4) 

Sicklepod (4) 

Broadleaf 

signalgrass (3) 

Goosegrass (3) 

Pigweed spp (3) 

Common cocklebur (2) 

Common lambsquarters (2) 

Common ragweed (2) 

Florida beggarweed (2) 

Palmer amaranth (2)

Texas millet (2) 

Bermudagrass (1) 

Crowfootgrass (1) 

Horseweed (marestail) (1) 

Jimsonweed (1) 

Johnsongrass (1) 

Smartweed spp. (1) 

Spurge spp (1) 

Volunteer peanut (1) 

Dicamba is effective on weeds highlighted in bold. 1

Source: (Webster et al. 2009). 

2

Number provided in parenthesis is the number of states out of the six total states (AL, FL, GA, NC, SC, & 

VA) in the Southeast Region reporting each weed as one of the ten most common weeds. 

Common weeds in Cotton Production in the Midsouth Region of the U.S.1,2

Morningglory spp (5) 

Broadleaf 

signalgrass (4) 

Crabgrass spp (4) 

Nutsedge spp (4) 

Prickly sida (4) 

Spurge spp (4) 

Pigweed spp (3)

Velvetleaf (3)

Barnyardgrass (2) 

Horseweed 

(marestail) (2) 

Johnsongrass (2) 

Palmer amaranth (2) 

Bermudagrass (1) 

Browntop millet (1) 

Common cockleburr (1) 

Cutleaf eveningprimrose (1) 

Goosegrass (1) 

Hemp sesbania (1) 

Henbit (1) 

Spurred anoda (1) 

Dicamba is effective on weeds highlighted in bold. 1

Source: (Webster et al. 2005; Webster et al. 2009) Webster et al., 2005 (MS & TN); Webster et al., 2009 

(AR, LA, & MO).

2

Number provided in parenthesis is the number of states out of the five total states (AR, LA, MS, MO, & 

TN) in the Midsouth Region reporting each weed as one of the ten most common weeds. 
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 48 of 53 

Common weeds in Cotton Production in the Southwest Region of the U.S.1,2

Johnsongrass (4) 

Nutsedge spp (4) 

Common 

cockleburr (3) 

Palmer amaranth (3) 

Silverleaf 

Nightshade (3) 

Common 

lambsquarters (2) 

Large Crabgrass (2) 

Devil's claw (2) 

Morningglory spp (2) 

Mustard spp (2) 

Pigweed spp (2) 

Russian thistle (2) 

Barnyardgrass (1) 

Bermudagrass (1) 

Bindweed, field (1) 

Foxtail spp (1) 

Groundcherry spp (1) 

Kochia (1) 

Horseweed 

(marestail) (1) 

Shepardspurse (1) 

Smartweed (1) 

Smellmelon (1) 

Spurred anoda (1) 

Red Sprangletop (1) 

Sunflower (1) 

Texas blueweed (1) 

Texas millet (2) 

Velvetleaf (1) 

Woolyleaf bursage (1) 

Dicamba is effective on weeds highlighted in bold. 1 Source: OK - (Webster et al. 2009); KS – Dr. Stewart Duncan, Kansas State University – Personal 

Communication 11/4/2010; NM – Dr. Jamshid Ashigh, New Mexico State University – Personal 

Communications 11/12/2010; TX – Dr. Wayne Keeling and Dr. Gaylon Morgan, Texas A&M University - 

Personal communications 11/4/2010. 

2 Number provided in parenthesis is the number of states out of the four total states (KS, OK, TX, & NM) 

in the Southwest Region reporting each weed as one of the ten most common weeds. 

Common weeds in Cotton Production in the West Region of the U.S.1,2

Barnyardgrass (2) 

Morningglory spp (2) 

Sprangletop (2) 

Bermudagrass (1) 

Field Bindweed (1) 

Cupgrass, 

southwestern (1) 

Groundcherry spp (1) 

Common 

lambsquarters (1) 

Johnsongrass (1) 

Junglerice (1) 

Nutsedge spp (1) 

Pigweed spp (1) 

Black Nightshade (1) 

Hairy Nightshade (1) 

Silverleaf 

Nightshade (1) 

Palmer amaranth (1) 

Common Purslane (1) 

Horse Purslane (1) 

Volunteer corn (1) 

Dicamba is effective on weeds highlighted in bold. 1 Source: AZ – Bill McCloskey, University of Arizona – Personal Communication 11/5/2010; CA – 

Steven Wright, University of California - Personal Communication 11/16/2010.

2 Number provided in parenthesis is the number of states out of the two total states (AZ & CA) in the 

West Region reporting each weed as one of the ten most common weed
Monsanto Company Petitions 10-188-01p/12-185-01p_a1 Page 49 of 53 

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