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Summary

The U.S. Environmental Protection Agency (EPA or the Agency) is proposing to grant an 

unconditional registration under Section 3(c)(5) of the Federal Insecticide, Fungicide, and 

Rodenticide Act (FIFRA) for the new uses of the herbicide dicamba on genetically-modified 

dicamba-tolerant cotton and genetically-modified dicamba-tolerant soybean. The proposed new 

uses will be added to the currently registered herbicide product M1691 (EPA Registration 

Number 524-582), containing 58.1% of the active ingredient dicamba, diglycolamine salt (DGA) 

for pre- and post-emergence (in-crop) applications to dicamba-tolerant cotton and soybean. 

The U.S. Department of Agriculture (USDA) granted deregulation status for dicamba-tolerant 

cotton and soybean on January 15, 2015 under the Plant Protection Act.

I. Chemical Information

Chemical Name: Dicamba (benzoic acid, 3,6-dichloro-2-methoxy-, aka 3,6-dichloro-o-anisic 

acid) 

EPA PC Code: 128931

Chemical Abstract Service (CAS) Number: 104040-79-1

Mode of Action: Dicamba is in the Benzoic Acid family that is used post-emergence for 

selective control of broadleaf weeds. Like the phenoxy herbicides, dicamba mimics auxins, a 

type of plant hormone and causes abnormal cell growth by affecting cell division. 

Registrant: Monsanto Company 

Proposed Product: M1691 Herbicide

Background

On April 28, 2010 and July 30, 2012, respectively, EPA received applications from the 

Monsanto Company (Monsanto) to register new uses of dicamba, as the DGA salt, on 

genetically-modified dicamba -tolerant soybean and cotton.

Dicamba is an active ingredient that is used through acid formulations and a variety of salt 

formulations, and is registered for a variety of food and feed uses. The proposed new uses on 

cotton and soybeans would expand the current timing of dicamba applications to dicambatolerant soybeans and cotton. Dicamba is currently registered for use on preplant and pre-harvest 

soybeans and on preplant and postharvest cotton. The proposed use would add post-emergence 

(over-the-top) applications to dicamba-tolerant cotton and soybean crops. 

Dicamba is a member of the Benzoic acid family of herbicides (Herbicide Resistance Action 

Committee (HRAC) Group 4). Dicamba works by increasing plant growth rate. Once sufficient 

concentration is reached, the plant outgrows its own nutrient supplies and ultimately dies. 

This proposal discusses several Agency considerations of the proposed use for dicamba on 

dicamba-tolerant soybeans and cotton, including discussions of human health and environmental 

risks associated with the proposed uses. Due to the multiple forms of dicamba, EPA considered 

all relevant data associated with the active ingredient when assessing its risks. For example, the 
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assessment for human health considered data associated with the BAPMA salt of dicamba, even 

though this registration action is being proposed for a formulation containing only the DGA salt 

of dicamba. This is because the data on the BAPMA salt was relevant to the analysis and resulted 

in the most conservative risk estimation to be used in each exposure scenario to be protective of 

all exposures of dicamba. On the other hand, assessments focus on effects of the DGA salt when 

product specific considerations are discussed. For example, to determine appropriate spray drift 

buffers, the Agency examined drift potential using studies conducted on the DGA salt 

formulation.

Proposed New Uses

Cotton

On currently registered dicamba products for use on conventional cotton, pre-emergence 

treatment can be made at 8 fluid ounces (0.25 lb a.e. dicamba) per acre per season. The 

maximum single/annual application rate proposed for use on dicamba-tolerant cotton for all 

preplant, at-planting, and pre-emergence applications is 32 fluid ounces (1.0 lb a.e. dicamba) per 

acre per season.

For the proposed new use, for post-emergence (in-crop) application of dicamba for use on 

dicamba-tolerant cotton, the maximum single in-crop application rate is 16 fluid ounces (0.5 lb 

a.e. dicamba) per acre. This rate is also the minimum single application in order to reduce the 

selection for resistant weeds. The maximum annual application rate for post-emergence in 

dicamba-tolerant cotton is 64 fluid ounces (2.0 lb a.e. dicamba) per acre. 

If a preplant application of 32 fluid ounces (1.0 lb a.e. dicamba) per acre is made, then the 

combined total post-emergence (in-crop) annual applications must not exceed 32 fluid ounces 

(1.0 lb a.e. dicamba) per acre for dicamba-tolerant cotton.

The combined total per year for all applications must not exceed 64 fluid ounces (2.0 lb a.e. 

dicamba) per acre. The minimum retreatment interval is 7 days; the pre-harvest retreatment 

interval for cottonseed including the livestock feeding of cotton gin by-products is 7 days.

Soybeans

On currently registered dicamba products, the maximum single and maximum annual application 

rate allowed to both conventional and dicamba-tolerant soybeans for all preplant, at-planting, and 

pre-emergence applications is 32 fluid ounces (1.0 lb a.e. dicamba) per acre per season.

For the proposed new use for post-emergence (in-crop) application of this product to dicambatolerant soybeans, the maximum single in-crop application rate is 16 fluid ounces (0.5 lb a.e. 

dicamba) per acre. This rate is also the minimum single application in order to reduce the 

selection for resistant weeds. The maximum annual application rate for post-emergence in 

soybeans is 32 fluid ounces (1.0 lb a.e. dicamba) per acre. 

The combined total per year for all applications must not exceed 64 fluid ounces (2.0 lb a.e 

dicamba) per acre. The minimum retreatment interval is 7 days; the pre-harvest interval, 

including feeding of soybean hay is 14 days (R1 Growth stage).
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Evaluation 

In evaluating a pesticide registration application, the EPA assesses a wide variety of information 

on the pesticide’s toxicity (i.e., effects on humans and other non-target organisms), exposure 

(i.e., where and how the pesticide is used), and environmental fate (i.e., how the chemical will 

move in the environment) to determine the likelihood of adverse effects (i.e., risk) to human 

health and the environment resulting from the proposed uses. Risk assessments are developed to 

evaluate the environmental fate of the compound as well as how it might affect a wide range of 

non-target organisms including humans, terrestrial and aquatic wildlife and plants. On the basis 

of these assessments, EPA evaluates and approves language for each pesticide label to ensure the 

directions for use and safety measures are appropriate to mitigate any potential risk. The 

pesticide’s label helps to communicate essential limitations and mitigations that are necessary for 

public safely. Once the risks are assessed and mitigation measures have been incorporated, EPA 

balances any remaining potential risks against the benefits of the use of the product. EPA will 

grant an application if it determines that the benefits of the use of the product outweigh its risks.

II. Human Health Risk

A summary of the human health risk assessment, Dicamba and Dicamba BAPMA Salt: HumanHealth Risk Assessment for Proposed Section 3 New Uses on Dicamba-tolerant Cotton and 

Soybean, is provided below.

As stated earlier in this document, the data associated with the BAPMA salt were considered to 

be the most appropriate form to use for assessing the potential for risks to human health. In the 

human health risk assessment for dicamba, risks were assessed in a manner that assures human 

health protection to all forms of the chemical. This is a complex analysis because (1) there are a 

variety of different forms of dicamba in registered or proposed to be registered products that 

must be considered (e.g., dicamba acid, dicamba BAPMA salt, other dicamba salts such as 

DGA), (2) the data showing greater toxicity for a major metabolite in foods (DCSA) relative to 

the parent compound, and (3) the different types of toxicity and potency seen with different 

routes of exposure (specifically, portal of entry effects observed in inhalation toxicity studies for 

BAPMA vs. other forms of dicamba). 

When determining the safety of a pesticide, EPA evaluates the available toxicity data and 

considers its validity, completeness, and reliability, as well as the relationship of the results of 

the studies to human risk. EPA also considers available information concerning the variability of 

the sensitivities of major identifiable sub-groups of consumers, including infants and children. 

Once a pesticide’s toxicological profile is determined, EPA identifies toxicological points of 

departure (POD) and levels of concern (LOC) to use in evaluating the risk posed by human 

exposure to the pesticide. For hazards that have a threshold below which there is no appreciable 

risk, the toxicological POD is used as the basis for derivation of reference values for risk 

assessment. PODs are developed based on a careful analysis of the doses in each toxicological 

study to determine the dose at which no adverse effects are observed (the NOAEL) and the 

lowest dose at which adverse effects of concern are identified (the LOAEL). Uncertainty/safety 

factors are used in conjunction with the POD to calculate a safe exposure level - generally 

referred to as a population-adjusted dose (PAD) or a reference dose (RfD) - and a safe margin of 

exposure (MOE). For non-threshold risks (e.g., cancer), the Agency assumes that any amount of 
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exposure will lead to some degree of risk. Thus, the Agency estimates risk in terms of the 

probability of an occurrence of the adverse effect expected in a lifetime (dicamba has been 

determined to be “not likely” to be carcinogenic and therefore a non-threshold approach does not 

apply in this case). For more information on the general principles EPA uses in risk 

characterization and a complete description of the risk assessment process, 

see http://www.epa.gov/pesticides/factsheets/riskassess.htm.

The following risk assessment endpoints were selected for dicamba to be protective to all forms 

of the chemical.

• For the acute dietary assessment, the most sensitive, single-day toxic effect seen across 

the entire dicamba database was chosen for quantifying risks, i.e., maternal neurotoxic 

effects seen in a developmental toxicity study in which animals were dosed with the 

BAPMA salt. Although dietary exposure could occur from agricultural use of other salts 

of dicamba resulting in lower risk estimates, the assessment quantified risks assuming 

everyone exposed to dicamba would be exposed to the more toxic BAPMA salt to assure 

protection from all forms of the chemical.

• For the chronic dietary assessment, the endpoint was selected from a reproduction study 

in which animals were dosed with the DCSA metabolite (a plant metabolite), a compound 

much more chronically toxic than any of the parent dicamba acid or salts pesticides. 

Although chronic dietary exposure could occur from exposure to various salts of dicamba 

rather than just this metabolite, risks were estimated assuming all residues in foods were 

the more toxic metabolite, thus assuring protection from all forms of the chemical.

• For the inhalation exposure assessment, risks were quantified separately for the BAPMA 

salt vs. other forms of dicamba since the BAPMA salt is (1) only used in agricultural 

settings and residential inhalation exposures would therefore not be expected, and (2) 

more toxic than other forms of dicamba with regard to portal of entry inhalation toxicity. 

• Finally, we assessed the toxicity specific to the counter-ion of the BAPMA salt, i.e., 

BAPMA itself. The potential for increased risk resulting from this chemical was assessed 

and determined to be low relative to the toxicity from the parent compounds and DCSA; 

therefore, protecting for exposures to the parent compounds and DCSA will also protect 

for exposures to BAPMA itself. 

A. Summary of Toxicological Effects

The toxicology database for dicamba is complete and sufficient for assessing the toxicity and 

characterizing the hazard of dicamba. Toxicology studies for dicamba acid, its salts 

[isopropylamine (IPA), diglycolamine (DGA), and N, N-Bis-(3-aminopropyl) methylamine 

(BAPMA)], and the plant metabolites [DCSA (3, 6-dichlorosalicylic acid) and DCGA (3, 6-

dichlorogentisic acid] were all considered for risk assessment of dicamba. In scenarios where 

co-exposure to the various forms could occur, the most protective point of departure (POD) was 

utilized.

Dicamba acid has been classified as having a low acute toxicity via oral, dermal and inhalation 

routes (Acute Toxicity Categories III or IV). It is both an eye and dermal irritant (Toxicity 

Category II), but it is not a skin sensitizer.
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Dicamba is classified as “not likely to be carcinogenic to humans” based upon the lack of 

evidence of carcinogenicity in mice and rats in the acid form when tested at adequate dose levels. 

The Agency determined, based on a reviews of epidemiological data (see Elizabeth Evans and 

Shanna Recore, Dicamba: Tier I (Scoping) Review of Human Incidents and Epidemiology, 

11/10/15), that the existing data did not support a conclusion that links human cancer to dicamba 

exposure.

B. Toxicological Endpoints and Doses Used in the Human Health Risk Assessment

Once a pesticide’s toxicological profile is determined, EPA identifies toxicological Points of 

Departure (POD) and Levels of Concern (LOC) to use in evaluating the risk posed by human 

exposure to the pesticide. For hazards that have a threshold below which there is no appreciable 

risk, the toxicological POD is used as the basis for derivation of reference values for risk 

assessment. PODs are developed based on a careful analysis of the doses in each toxicological 

study to determine the dose at which no adverse effects are observed (the No Observed Adverse 

Effect Level (NOAEL)) and the lowest dose at which adverse effects of concern are identified 

(the Lowest Observed Adverse Effect Level (LOAEL)). Uncertainty factors (UF)/safety factors 

(SF) are used in conjunction with the POD to calculate a safe exposure level – generally referred 

to as a Population-adjusted Dose (PAD) or a Reference Dose (RfD) – and a safe Margin of 

Exposure (MOE). For non-threshold risks, EPA assumes that any amount of exposure will lead 

to some degree of risk. Thus, EPA estimates risk in terms of the probability of an occurrence of 

the adverse effect expected in a lifetime. 

1. Acute Dietary

The acute dietary endpoint was selected from the dicamba BAPMA salt rat developmental 

toxicity study, which represents the most sensitive endpoint in the dicamba toxicology database 

resulting from a single-dose dietary exposure. The NOAEL is 29 mg/kg/day, and the LOAEL is 

86 mg/kg/day based on ataxia, unsteady gait, and convulsions in female rats. This NOAEL POD 

is protective of acute effects of dicamba via the oral route of exposure to the general population, 

including infants and children. A separate acute dietary endpoint for reproductive females ages 

13-49 is not required since no acute developmental toxicity effects were observed in the dicamba 

database. An uncertainly factor of 100X was applied with 10X for interspecies extrapolation 

from animal to human, and 10X for intraspecies variation in sensitivity amongst the human 

population. As discussed in Section C below, the Food Quality and Protection Act (FQPA) safety 

factor was reduced to 1X, resulting in an aRfD/aPAD of 0.29 mg/kg/day.

2. Chronic Dietary

The chronic dietary endpoint was selected from the DCSA plant metabolite reproduction toxicity 

study, which represents the most sensitive endpoint in the toxicology database resulting from 

repeated-dose dietary exposure. The NOAEL is 4 mg/kg/day, and the LOAEL is 37 mg/kg/day 

based on decreased pup weights. The NOAEL POD is protective of chronic effects of dicamba 

via the oral route of exposure to the general population, including infants and children. A 100X 

UF was applied (10X interspecies and 10X intraspecies), and the FQPA SF was reduced to 1X 

resulting in a cRfD/cPAD of 0.04 mg/kg/day. 
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3. Incidental Oral (Short- and Intermediate-Term)

The incidental oral endpoint was selected from the dicamba acid rat multi-generation 

reproductive toxicity study, which represents the most appropriate endpoint in the toxicology 

database for assessing short- (1 to 30 days) and intermediate-term (1 to 6 months) incidental oral 

(hand-to-mouth) exposure. The NOAEL is 136 mg/kg/day, with a LOAEL of 450 mg/kg/day 

based on impaired pup growth. A 100X UF was applied (10X interspecies and 10X intraspecies), 

and the FQPA SF was reduced to 1X resulting in a level of concern of 100.

4. Inhalation (All Durations)

For dicamba acid and the DGA salt inhalation risk assessment for short and intermediate term 

durations, the POD was based on the route-specific dicamba acid inhalation toxicity study in 

Wistar rats with a LOAEL of 0.050 mg/L based on local effects of hyperplasia in the lungs and 

lymph nodes (NOAEL = 0.005 mg/L, non-systemic, pulmonary regional deposited dose ratio 

(RDDR) = 0.590).

The standard interspecies extrapolation UF can be reduced from 10X to 3X for dicamba acid due 

to the calculation of human equivalent concentrations (HECs) accounting for pharmacokinetic 

(not pharmacodynamic) interspecies differences. Therefore, the LOC for dicamba acid inhalation 

exposures is for MOEs less than 30 (3X for interspecies extrapolation, 10X for intraspecies 

variation, and 1X for FQPA SF when applicable). The inhalation HEC/HED results are listed in 

Appendix A.5.

5. Dermal (All Durations)

No dermal endpoint was selected since no adverse effects were observed in the subchronic 

dermal studies for dicamba acid, IPA salt, and DGA salt up to the limit dose. 

6. Cancer

Dicamba is classified as “Not Likely to be Carcinogenic to Humans.” This decision was based on 

the lack of findings in the cancer studies in rats and mice, which were tested at adequate dose 

levels to assess the carcinogenicity of dicamba. Mutagenicity studies generally did not 

demonstrate evidence of mutagenic potential for dicamba and the concern for genotoxicity in the 

acid form is low. Epidemiology studies were also examined and no links were found to dicamba 

exposure and cancer. Additionally, the DCSA metabolite also had a lack of findings in a 

chronic/carcinogenicity study in rats.

C. FQPA Safety Factor

EPA has determined that the 10X FQPA Safety Factor for protection of infants and children, 

mentioned above, can be reduced to 1X for the acute and chronic dietary risk assessment for the 

following reasons and discussed in more detail below: (1) The toxicity database for dicamba is 

complete with respect to the required 870 guideline studies. (2) For dicamba, there is no 
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evidence of increased susceptibility following in utero exposures to rats and rabbits and 

following pre and/or post-natal exposure to rats in a two-generation reproduction study. 

For the dicamba acid and BAPMA salt, no developmental toxicity was seen at the highest doses 

tested in the prenatal developmental studies with rats. (3) Consistent neurotoxic signs (e.g., 

ataxia, decreased motor activity, impaired righting reflex and gait) were observed in multiple 

studies in rats and rabbits.

After considering the available toxicity data, EPA determined that there is no need for a 

developmental neurotoxicity study or additional UFs to account for neurotoxicity due to the 

following: (1) although clinical signs of neurotoxicity were seen in pregnant animals, no 

evidence of developmental anomalies of the fetal nervous system were observed in the prenatal 

developmental toxicity studies, in either rats or rabbits, at maternally toxic doses up to 300 or 

400 mg/kg/day, respectively; (2) there was no evidence of behavioral or neurological effects on 

the offspring in the two-generation reproduction study in rats; (3) the ventricular dilation of the 

brain in the combined chronic toxicity and carcinogenicity study in rats was only observed in 

females at the high dose after two years of exposure at doses of 127 mg/kg/day. The significance 

of this observation is questionable, since no similar histopathological findings were seen in two 

sub-chronic neurotoxicity studies at the limit dose or other chronic studies.

There are no residual uncertainties identified in the exposure databases. The acute dietary food 

exposure assessment was performed using tolerance level residues and 100% crop treated 

assumptions. The chronic dietary food exposure assessment used average residues for crops, 

tolerances levels for livestock commodities, and percent crop treated assumptions for several 

registered uses. Conservative ground and surface water estimates calculated using the latest 

models were used. Similarly, conservative residential Standard Operating Procedure (SOPs) 

were used to assess post-application exposure of children as well as incidental oral exposure of 

toddlers. These assessments will not underestimate the exposure and risks posed by dicamba.

1. Completeness of the Toxicology Database

The toxicity database for dicamba is adequate to characterize the potential for prenatal or 

postnatal risk to infants and children. Acceptable rat and rabbit developmental toxicity studies, 

two rat 2-generation reproduction studies, and acute/subchronic neurotoxicity studies in rats are 

available.

2. Evidence of Neurotoxicity

There is evidence of neurotoxicity resulting from exposure to dicamba throughout the toxicology 

database (i.e., impaired gait, impaired righting reflex, ataxia, decreased motor activity, rigidity 

upon handling, etc). These signs of neurotoxicity were observed in multiple studies in rats and 

rabbits. However, after considering the available toxicity data, the Agency determined that a 

developmental neurotoxicity study (DNT) is not required for the following reasons: (1) although 

clinical signs of neurotoxicity were seen in pregnant animals, no evidence of developmental 

anomalies of the fetal nervous system were observed in the prenatal developmental toxicity 

studies, in either rats or rabbits, at maternally toxic doses up to 300 or 400 mg/kg/day, 

respectively; (2) there was no evidence of behavioral or neurological effects on the offspring in 
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the two-generation reproduction study in rats; (3) the ventricular dilation of the brain in the 

combined chronic toxicity and carcinogenicity study in rats was only observed in females at the 

high dose after two years of exposure at doses of 127 mg/kg/day. The significance of this 

observation is questionable, since no similar histopathological finding was seen in two subchronic neurotoxicity study at the limit dose or other chronic studies.

3. Evidence of Sensitivity/Susceptibility in the Developing or Young Animal

There is no evidence of susceptibility to the young following in utero exposure to dicamba acid, 

dicamba BAPMA or DCSA. Quantitative offspring susceptibility was observed in the 2-

generation reproduction study for the DCSA metabolite based on decreased pup weights, which 

occurred at a dose at which no parental effects were observed. However, the degree of concern 

for the susceptibility is low, because there is a well-established NOAEL for offspring toxicity in 

that study and DCSA has rapid clearance. Additionally, the current points of departure are health 

protective and therefore address the concern for offspring toxicity observed in the reproduction 

studies.

4. Residual Uncertainty in the Exposure Database

The residential exposure assessment assumes maximum label use rate as well as other 

conservative assumptions. The acute dietary exposure assessment is based on an exaggerated 

exposure scenario which assumes that all commodities being consumed retain tolerance level 

residues, and the chronic dietary exposure assessment assumes field trial residues in which the 

crops were treated using the use patterns likely to lead to maximum residues. Additionally, the 

drinking water estimates utilized conservative models. Therefore, the Agency does not believe 

that exposure to dicamba will be underestimated.

D. Cumulative effects

EPA has not made a common mechanism of toxicity finding for dicamba and any other 

substance, and dicamba does not appear to produce a toxic metabolite produced by other 

substances. For the purposes of this Proposed Registration Decision, therefore, EPA has assumed 

that dicamba does not have a common mechanism of toxicity with other substances. For 

information regarding EPA’s efforts to determine which chemicals have a common mechanism 

of toxicity and to evaluate the cumulative effects of such chemicals, see the policy statements 

released by EPA’s Office of Pesticide Programs concerning common mechanism determinations 

and procedures for cumulating effects from substances found to have a common mechanism on 

EPA’s website at https://www.epa.gov/pesticide-science-and-assessing-pesticiderisks/cumulative-assessment-risk-pesticides.

E. Dietary (Food + Drinking Water) Risk

Dicamba is a selective systemic herbicide used to control a variety of broadleaf weeds and 

registered for a variety of food/feed uses. Permanent tolerances for dicamba are established 

under 40 CFR § 180.227 for a wide variety of crops and livestock commodities.
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Acute and chronic aggregate dietary food and drinking water exposure and risk assessments were 

conducted using the Dietary Exposure Evaluation Model software with the Food Commodity 

Intake Database (DEEM-FCID) Version 3.16. This software uses 2003-2008 food consumption 

data from the U.S. Department of Agriculture’s (USDA’s) National Health and Nutrition 

Examination Survey, What We Eat in America, (NHANES/WWEIA).

1. Acute Dietary Risk

For acute exposure assessments, individual one-day food consumption data are used on an 

individual-by-individual basis. The reported consumption amounts of each food item are 

multiplied by a residue point estimate and summed to obtain a total daily pesticide exposure for a 

deterministic exposure assessment, or “matched” in multiple random pairings with residue values 

and then summed in a probabilistic assessment. The resulting distribution of exposures is 

expressed as a percentage of the aPAD on both a user basis (i.e., only those who reported eating 

relevant commodities/food forms) and a per-capita basis (i.e., those who reported eating the 

relevant commodities as well as those who did not). In accordance with EPA policy, per capita 

exposure and risk are reported for analyses.

Risks are considered to be of no concern when they are less than 100% of the aPAD or cPAD, a 

value determined by dividing the point of departure for the most sensitive and pertinent 

toxicological effect for each exposure scenario by required uncertainty factors. The acute 

analysis was an unrefined determination which used tolerance level residues and assumed 100 

percent crop treated (%CT) for all existing and proposed uses. The dietary exposure analyses that 

were performed result in acute dietary risk estimates that are below the Agency’s LOC for both 

food and water. For the U.S. population the exposure was 0.042760 mg/kg/day, which utilized 

15% of the acute population adjusted dose (aPAD) at the 95th percentile. The highest exposure 

and risk estimates were for all infants (<1 year old). At the 95th percentile, the exposure for all 

infants (<1 year old) was 0.089 mg/kg/day, which utilized 31% of the aPAD.

2. Chronic Dietary Risk

For chronic dietary exposure assessment, an estimate of the residue level in each food or foodform (e.g., orange or orange juice) on the food commodity residue list is multiplied by the 

average daily consumption estimate for that food/food form to produce a residue intake estimate. 

The resulting residue intake estimate for each food/food form is summed with the residue intake 

estimates for all other food/food forms on the commodity residue list to arrive at the total 

average estimated exposure. Exposure is expressed in mg/kg body weight/day and as a percent of 

the cPAD. This procedure is performed for each population subgroup.

The chronic analysis was a partially refined determination which used average residues based on 

field trial studies for crops, tolerance levels for livestock commodities, and relevant % crop 

treated (CT) data for several existing uses. The chronic risk estimates for dicamba are below the 

Agency’s LOC for the general U.S. population and all population subgroups. The highest 

exposure and risk estimates were for the population subgroup of children ages 1-2 with a risk 

estimate for dicamba for food and water of 42% of the cPAD. 
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F. Residential (Non-Occupational) Exposure/Risk Characterization

There are no residential uses being proposed for dicamba with this current registration; however, 

there are existing residential uses of dicamba that have been reassessed in this document to 

reflect updates to HED’s 2012 Residential SOPs along with policy changes for body weight 

assumptions. The revision of residential exposures will impact the human health aggregate risk 

assessment for dicamba. Registered uses of dicamba include solid and liquid products in 

concentrates or ready-to-use sprays for use as spot and broadcast treatments on turf.

1. Residential Handler Exposure

Based on the currently registered uses, residential handlers may receive exposure to dicamba 

when mixing, loading and applying the pesticide to lawns and turf. Since there was no dermal 

hazard identified for dicamba, only inhalation risk estimates were quantitatively assessed. The 

inhalation risk estimates were based on the following application scenarios:

• Mix/Load/Apply Liquid with Hand-held Equipment

• Apply Ready-To-Use Sprays with Hand-held Equipment

• Load/Apply Granules with Hand-held Equipment

The MOEs for the exposure scenarios assessed range from 190 to 220,000. Since there is 

potential risk concern only when inhalation MOEs are less than a LOC of 30, residential handler 

exposures are not a concern.

2. Post-application Exposure

There is the potential for post-application exposure for individuals exposed as a result of being in 

an environment that has been previously treated with dicamba. Since no dermal hazard was 

identified for dicamba, the quantitative exposure/risk assessment for residential post-application 

exposures is based on the following scenarios:

• Children (1 to < 2 years old) incidental oral exposure to treated turf.

• Children (1 to < 2 years old) episodic granular ingestion exposure.

The assessment of post-application exposure to liquid formulations is protective of exposure to 

solid formulations, except for the episodic granular ingestion scenario which was quantitatively 

assessed. The life stages selected for assessment are health protective for the exposures and risk 

estimates for any other potentially exposed life stages.

The post-application assessment for turf includes only the incidental oral routes of exposure. The 

series of assumptions and exposure factors that served as the basis for completing the residential 

post-application risk assessment are detailed in the 2012 Residential SOPs 

(https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/standard-operatingprocedures-residential-pesticide). In addition, chemical-specific residue data were used in the 

assessment. The residential post-application risk estimates are not of concern for dicamba since 

all MOEs are greater than the LOC of 100 (the lowest MOE = 6600 for use of liquids on lawns).
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3. Residential Bystander Post-application inhalation exposure

The potential exposure to bystanders from vapor phase dicamba residues emitted from treated 

fields has been evaluated for the proposed uses of dicamba on dicamba-tolerant corn and 

soybean. Bystander exposure to dicamba emitted from treated fields depends on two main 

factors: 1) the rate at which these chemicals volatilize from a treated field (described as the offgassing, emission or flux), and 2) how those vapors are dispersed in the air over and around the 

treated field. Volatilization can occur during the application process or thereafter. It can result 

from aerosols evaporating during application, while deposited sprays are still drying (possibly 

via co-distillation), or after as dried deposited residues volatilize. 

Volatilization modeling for a single day was completed using the Probabilistic Exposure and 

Risk model for Fumigants (PERFUM). There are a variety of factors that potentially affect the 

emission rates of dicamba and subsequent offsite transport including: field condition (bare soil, 

growing or mature crop canopy), field parameters (soil type, moisture, etc.), formulation type, 

meteorological conditions, and application scenario (rate, method). 

A chemical-specific flux study was used to estimate a flux rate of 0.0004 ug/m2

/s for dicamba. 

This flux rate, along with an assumption of a single 40 acre field, and using Bradenton, FL 

meteorological data from Bradenton, FL were used with PERFUM to estimate risk.

The field volatility study suggests that volatilization of dicamba from treated crops does occur, 

which could result in bystander exposure. Results of PERFUM modeling, however, indicate that 

airborne concentrations are negligible, and even at the edge of the treated fields risk estimates are 

not of concern.

4. Spray Drift

Spray drift is always a potential source of exposure to residents nearby to spraying operations. 

Off-target movement of pesticides can occur via many types of pathways and it is governed by a 

variety of factors. Sprays that are released and do not deposit in the application area end up offtarget and can lead to exposures to those it may directly contact. They can also deposit on 

surfaces where contact with residues can eventually lead to indirect exposures (e.g., children 

playing on lawns where residues have deposited next to treated fields). The potential risk 

estimates from these residues are calculated using drift modeling coupled with methods 

employed for residential risk assessments for turf products.

The approach to be used for quantitatively incorporating spray drift into risk assessments is 

based on a premise of compliant applications which, by definition, should not result in direct 

exposures to individuals because of existing label language and other regulatory requirements 

intended to prevent them. Direct exposures would include inhalation of the spray plume or being 

sprayed directly. Rather, the exposures addressed here occur indirectly through contact with 

impacted areas, such as residential lawns, when compliant applications are conducted. Given this 

premise, exposures for children (1 to 2 years old) and adults who have contact with turf where 

residues are assumed to have deposited via spray drift thus resulting in an indirect exposure are 

the focus of this analysis, analogous to how exposures to turf products are considered in risk 

assessment.
13

Several dicamba products have existing labels for use on turf, thus it was considered whether the 

risk assessment for that use would be considered protective of any type of exposure that would 

be associated with spray drift. Because the registered residential uses on turf result in exposure 

greater than potential exposure from spray drift, no new residential assessment needs to be 

completed. If the maximum application rate on crops adjusted by the amount of drift expected is

less than or equal to existing turf application rates, the existing turf assessment is considered 

protective of spray drift exposure. The proposed maximum single application rate of dicamba is 

1 lb ae/A. The highest degree of spray drift noted for any application method immediately 

adjacent to a treated field (Tier 1 output from the aerial application using fine to medium spray 

quality) results in a deposition fraction of 0.26 of the application rate. For the purposes of the 

proposed uses on dicamba, this is considered a screening level assumption since the proposed 

use is for groundboom applications only. A quantitative spray drift assessment for dicamba is not 

required because the maximum application rate to a crop/target site multiplied by the adjustment

factor for drift of 0.26 is less than the maximum direct spray residential turf application rate 1 lb 

ae/A for any dicamba products. The turf post-application MOEs have been previously assessed, 

are based on the revised SOPs for Residential Exposure Assessment, and were not found to be of 

concern, as noted above.

5. Aggregate Risk Assessment

In accordance with the FFDCA, HED must consider and aggregate (add) pesticide exposures and 

risks from three major sources: food, drinking water, and residential exposures. In an aggregate 

assessment, exposures from relevant sources are added together and compared to quantitative 

estimates of hazard, or the risks themselves can be aggregated. When aggregating exposures and 

risks from various sources, HED considers both the route and duration of exposure. Since 

residential exposure is expected, aggregate exposure consists of exposure from residential, food 

and drinking water sources.

Acute and chronic aggregate risks include only dietary exposure from food and drinking water 

sources. Since there are residential uses, short-term aggregate risks were assessed which include 

contributions from food, drinking water, and residential exposure. Intermediate-term aggregate 

risks were not considered as residential exposure is not expected to occur for more than 30 days. 

Cancer aggregate risk was not quantified since dicamba is not a carcinogen. A common 

toxicological endpoint of concern was not identified for short-, intermediate- and long-term 

durations via the oral, dermal, and inhalation routes. Therefore, the aggregate exposure risk 

assessment should include exposure across the oral routes only, as appropriate for the 

populations of concern (i.e., food and water for adults; and food, water and incidental oral for 

children).

a. Acute Aggregate Risk

The acute aggregate risk assessment includes only food and water exposure; therefore, the acute 

dietary (food and drinking water) assessment represents acute aggregate risk. The acute dietary 

exposure assessment was conducted using tolerance-level residues, DEEM default processing 

factors and 100% crop-treated information for all registered and proposed use sites. Drinking 

water values were incorporated directly into the assessment. 
14

The most highly exposed population subgroup is all infants (<1 year old; 31% of the aPAD). The 

acute dietary exposure estimates are not of concern for the general U.S. population or any 

population subgroup.

b. Short-term aggregate risk

The short-term aggregate risk assessment includes food, water and residential exposure. The 

resulting short-term aggregate risks are not of concern for children (MOEs > LOC 100). For 

adults, since there was no dermal hazard identified in the route-specific dermal studies and the 

inhalation effects were not systemic, the chronic dietary assessment is protective for short term 

aggregate risks.

6. Long-term aggregate risk

The chronic (long-term) aggregate risk assessment includes only food and water exposure. The 

chronic dietary analysis was a partially refined determination which used average residues based 

on field trial studies for crops, tolerance levels for livestock commodities, and relevant % crop 

treated (CT) data for several existing uses. The chronic risk estimates for dicamba are below the 

Agency’s LOC for the general U.S. population and all population subgroups. The highest 

exposure and risk estimates were for the population subgroup of children ages 1-2 with a risk 

estimate for dicamba for food and water of 42% of the cPAD.

7. Occupational Risk Assessment 

a. Short- and Intermediate-term handler Risk

EPA uses the term occupational handler to describe people who mix, load and/or apply 

pesticides professionally (e.g., farmers, professional pesticide applicators). Based on the 

anticipated use patterns and current labeling, types of equipment and techniques that can 

potentially be used (e.g., mixing/loading liquids for ground boom application, and applying 

sprays by ground boom equipment), occupational handler exposure is expected from the new 

uses. 

The occupational handler risk estimates are not of concern (i.e., MOEs > LOC of 30) for all of 

the scenarios for the use of dicamba on genetically -modified cotton and soybean. At baseline 

personal protective equipment (PPE) (i.e., no respirator), the occupational handler inhalation 

MOEs are 380 for mixer/loaders and 250 for applicators using ground boom equipment. 

b. Short and Intermediate term Post-application Risk

EPA uses the term post-application to describe exposures that occur when individuals are present 

in an environment that has been previously treated with a pesticide (also referred to as reentry 

exposure). Such exposures may occur when workers enter previously treated areas to perform 

job functions, including activities related to crop production, such as scouting for pests or 

harvesting. Post-application exposure levels vary over time and depend on such things as the 

type of activity, the nature of the crop or target that was treated, the type of pesticide application, 

and the chemical’s degradation properties. In addition, the timing of pesticide applications, 

relative to harvest activities, can greatly reduce the potential for post-application exposure.
15

i. Dermal Post-application Risk

There is no potential hazard via the dermal route for dicamba; therefore, a quantitative 

occupational post-application dermal risk assessment was not completed.

ii. Inhalation post application Risk

There are multiple potential sources of post-application inhalation exposure to individuals 

performing post-application activities in previously treated fields. These potential sources 

include volatilization of pesticides and resuspension of dusts and/or particulates that contain 

pesticides. The Agency sought expert advice and input on issues related to volatilization of 

pesticides from its Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel 

(SAP) in December 2009, and received the SAP’s final report on March 2, 2010 

(http://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2009-0687-0037. The Agency 

has evaluated the SAP report and has developed a Volatilization Screening Tool and a 

subsequent Volatilization Screening Analysis 

(https://www.regulations.gov/#!documentDetail;D=EPA-HQ-OPP-2014-0219-0002). During 

Registration Review, the Agency will utilize this analysis to determine if additional data (i.e., 

flux studies, route-specific inhalation toxicological studies) or further analysis is required for the 

active ingredient dicamba, generically.

In addition, the Agency is continuing to evaluate the available post-application inhalation 

exposure data generated by the Agricultural Reentry Task Force. Given these two efforts, the 

Agency will continue to identify the need for and, subsequently, the way to incorporate 

occupational post-application inhalation exposure into the Agency's risk assessments. 

III. Environmental Risk

A summary of the environmental fate and ecological effects, and potential environmental risks 

from the use of dicamba on dicamba-tolerant soybean and cotton is provided below. More 

detailed discussions can be found in the Agency documents titled, Ecological Risk Assessment 

for Dicamba and its Degradate, 3,6-dichlorosalicylic acid (DCSA), for the Proposed New Use 

on Dicamba-Tolerant Soybean (MON87708) and Ecological Risk Assessment for Dicamba DGA 

Salt and its Degradate, 3,6-dichlorosalicylic acid (DCSA), for the Proposed Post-Emergence 

New Use on Dicamba-Tolerant Cotton (MON 87701), and its addendums entitled, Addendum to 

the Environmental Fate and Ecological Risk Assessment for the Section 3 New Use of on 

Dicamba-Tolerant Soybean and Dicamba DGA; Second Addendum to the Environmental Fate 

and Ecological Risk Assessment for Dicamba DGA salt and its Degradate, 3,6-dichlorosalicylic 

acid (DCSA) for the Section 3 New Use on Dicamba-Tolerant Soybean. These documents are in 

the docket. A fuller description of how these potential risks are assessed can be found 

at: https://www.epa.gov/pesticide-science-and-assessing-pesticide-risks/ecological-riskassessment-pesticides-technical.

A. Environmental Fate

1. Degradation

Dicamba is generally stable to abiotic processes, and is more persistent under anaerobic 

conditions. It is stable to abiotic hydrolysis at all pH levels and photodegrades slowly in water 
16

and soil. Under anaerobic soil conditions, the dicamba parent molecule has a half-life of 141 

days. It is not persistent under aerobic conditions; aerobic soil metabolism is the main 

degradative process for dicamba, with a half-life of 6 days. Dicamba was found in two 

acceptable field dissipation studies in soil segments deeper than 10 cm with half-lives ranging 

from 4.4 to 19.8 days. In aquatic systems, dicamba degrades more rapidly when sediment is 

present and has an aerobic soil metabolism half-life in sediment-water system of ~24 days. 

The major degradate of dicamba is 3,6-dichlorosalicylic acid (DCSA). It is persistent when 

formed under anaerobic conditions, comprising more than 60% of the applied dose after 365 

days of anaerobic incubation in sediment-pond water system. DCSA is not persistent when 

formed under aerobic conditions and degrades roughly at the same rate as the parent dicamba

with a half-life of 8.2 days. Like the parent molecule, DCSA is mobile and was also found in the 

two acceptable field studies in soil segments deeper than 10 cm. If it were to reach anaerobic 

groundwater, it would likely persist; however, EPA does not expect DCSA to reach groundwater 

at levels that would be of concern. DCSA is formed in aerobic soil under laboratory conditions at 

the maximum of 17.4 % of the applied parent dose. Other minor dicamba degradates of concern 

are DCGA and 5-OH-dicamba, and both are less toxic than the parent molecule and DCSA. The 

formation of DCGA in the laboratory studies did not exceed 3.64%, and the formation of 5-OH 

dicamba did not exceed 1.9 % in soil-water system during anaerobic aquatic degradation of 

dicamba under laboratory conditions. DCSA was also a major metabolite in plant metabolism 

and magnitude of residue studies for dicamba-tolerant soybean and cotton, comprising 

approximately 80% and 20%, respectively, of dicamba-related residues in plant tissues for these 

crops.

2. Mobility

Dicamba is very soluble and mobile. It may reach surface water via field/site runoff, spray drift 

during application, and by vapor drift from volatilization. It is not expected to bioaccumulate in 

aquatic organisms as it is an anion at environmental pHs. Since dicamba is not persistent under 

aerobic conditions, very little dicamba is expected to reach groundwater. The major degradage of 

dicamba, DCSA, is persistent under anaerobic conditions; however EPA does not expect DCSA 

to reach groundwater at levels that would be of concern. The major route of exposure to nontarget organisms is likely spray drift and runoff. Also, multiple literature studies show that there 

is a high vapor drift from soybean fields resulting in non-target plant injury. The assessments 

related to these routes of exposure are described in the sections below. 

3. Runoff

The Agency has considered the potential effects due to runoff, and has developed proposed 

mitigation to limit off-site runoff. A component of the model used to assess terrestrial risk 

assumes that the mass of pesticide running off the treated field is directly related to the 

pesticide’s solubility in water. In the case of dicamba DGA salt, the dissociated salt yields 

highly soluble dicamba acid. The model assumes that the high solubility of the acid results in a 

runoff mass of 5 percent of the field-applied mass, which is considered to be a highly 

conservative estimate because the model does not account for loss of chemical from degradation, 

partitioning, or the temporal aspects of runoff (e.g., a rain event following application that 

exceeds soil’s field capacity). 
17

4. Spray Drift 

The Agency considers spray drift exposure to be the principal risk issue associated with the 

proposed label use of dicamba DGA salt, owing to a variety of lines of evidence, including past 

experience with other dicamba formulations. In addition, visual observations of off-field plant 

damage have been reported following dicamba applications, likely the result of subsequent spray 

drift and/or volatilization of dicamba residues.

The Agency used a weight of evidence approach incorporating spray drift modeling, a spray drift 

droplet deposition study, and raw data from field trials to determine an appropriate in-field buffer 

to avoid dicamba exposure to non-target organisms (e.g., endangered plants). EPA has also 

determined that the label must specify that nozzles must be used that produce extra-course and 

ultra-course droplet spectra for application to reduce the potential for spray drift. Based on the 

weight of evidence approach, EPA determined that labels must include language to maintain an 

in-field buffer (to the edge of the field in all directions) of 100 feet when applying at the 0.5 lb 

a.e./A application rate and 220 feet when applying at the 1.0 lb a.e./A application rate in order to 

restrict the movement of residues to the field. Using these buffers, expected residues at the field's 

edge from spray drift would be below apical endpoints for the most sensitive tested species (i.e.

NOAEC for soybean plant height).

5. Volatilization

After reviewing submitted data relating to the volatility of dicamba, the Agency had concerns 

regarding the volatility of dicamba, and possible post-application, vapor-phase off-site transport 

that might damage non-target plants. Monsanto responded to these concerns with a submission 

that acknowledged the long-recognized volatility of dicamba acid and described measurements 

of the volatilization in the different formulations.

Though the Agency found the information helpful, the submission did not include enough detail 

to verify the measurements in the studies. Therefore, in order to be protective of potential effects 

to non-target plants from volatilization, labels must include language to maintain an in-field 

buffer (to the edge of the field in all directions) of 100 feet when applying at the 0.5 lb a.e./A 

application rate and 220 feet when applying at the 1.0 lb a.e./A application rate. Although the 

Agency is not requiring additional data to be submitted at this time, if EPA receives volatility 

data under varied conditions of temperature and relative humidity, as these factors play a strong 

role in volatility under field conditions, it may reconsider whether this mitigation requirement is 

necessary.

EPA is aware that for use of dicamba in Arkansas, the Arkansas Plant Board has an in-field 

buffer that is greater than what is being proposed by EPA (400 feet as opposed to 110 to 220 

feet). EPA has reviewed the information associated with the larger buffer in Arkansas to assess 

why these differences exist. EPA’s buffer is determined by evaluation of plant toxicity data 

required under FIFRA and conducted under GLP conditions where apical endpoints, plant 

height, and yield, are used as measures of plant growth and reproduction. Once the no observed 

adverse effect concentration (NOAEC) was determined for the most sensitive endpoint (i.e.,

plant height) for the most sensitive plant species tested (i.e., soybeans), EPA uses field studies 

and modeling to determine the distance from site of application to where the NOEC is not 

expected to be exceeded. It is further noted that the labels for the proposed uses will specify a 

spray nozzle and pressure combination that is expected to reduce drift of the herbicide, which are 
18

drift reduction measures not on the previously registered dicamba formulations and could also 

influence the size of a protective buffer. In telephone conversations between EPA and the 

Arkansas Plant Board, it was reported that Arkansas’ buffer distance of 400 feet was not 

computed as a result of submitted data, but as a precautionary measure that was based on 

information and observations from extension specialists from Arkansas and neighboring states, 

discussions with Monsanto, and historical information involving qualitative visual observations 

of damage in the field with products not containing the specific nozzle and pressure requirements 

contained on the proposed label. The Arkansas Plant Board felt that a 400 foot buffer should 

exceed what would be necessary to protect neighboring crop fields that are directly adjacent to 

fields receiving dicamba treatment. The Arkansas Plant Board also reports that their buffer 

requirement may be revisited and/or removed after a period of initial use (if registered) once 

additional observations are made. 

B. Ecological Risk

Ecological risk characterization integrates the results of the exposure and ecotoxicity data to 

evaluate the likelihood of adverse ecological effects. The process of integrating the results of 

exposure with the ecotoxicity data is called the risk quotient method. For this method, risk 

quotients (RQs) are calculated by dividing exposure estimates by ecotoxicity values, both acute 

and chronic (RQ = Exposure / Toxicity). RQs are then compared to EPA’s levels of concern 

(LOCs). The LOCs are criteria used by the Agency to indicate potential risk to non-target 

organisms. The criteria indicate whether a pesticide, when used as directed, has the potential to 

cause adverse effects to non-target organisms.

For terrestrial animals, the Agency’s acute risk LOCs are set at 0.5 for non-listed species and 0.1 

for listed species. For aquatic animals, acute risk LOCs are also set at 0.5 for non-listed species 

but for listed species, they are set at 0.05. The chronic risk LOC is set at 1.0 for both terrestrial 

and aquatic animals. For plants, acute risk LOCs are set at 1 for both non-listed and listed 

species. The potential difference in sensitivity for listed plant species compared to non-listed 

plant species is addressed through the use of different toxicity endpoints in the RQ equation [the 

concentration causing effects to 25% of the test population (EC25) for non-listed plants vs the 

NOEC or concentration causing effects to 5% of the test population (EC05) for listed species]. 

Chronic risk is not assessed for plants.

Dicamba is currently registered for use on several food and non-food use sites, including cotton 

and soybean. The proposed uses on dicamba-tolerant soybeans and cotton would expand the 

timing of applications from pre-emergence and pre-harvest only for soybeans and pre-emergence 

and post-harvest only for cotton to allowing post-emergence over-the-top applications. The 

maximum yearly application rates would remain 2.0 lb a.e./acre for both cotton and soybeans. 

However, as detailed in section I of this document, the applicator could now split the 2.0 lb 

a.e./acre between pre-emergence and post-emergence applications.

EPA has a specific process based on sound science that it follows when assessing risks to listed 

species for pesticides like dicamba that will be used on seeds that have been genetically modified 

to be tolerant to the pesticide. The Agency begins with a screening level assessment that includes

a basic ecological risk assessment based on its 2004 Overview of the Ecological Risk 

Assessment Process document. [USEPA, 2004, available at 

http://www.epa.gov/oppfead1/endanger/litstatus/riskasses.htm]. That assessment uses broad 
19

default assumptions to establish estimated environmental concentrations of particular pesticides. 

If the screening level assessment results in a determination that no levels of concern are 

exceeded, EPA concludes its analysis. On the other hand, where the screening level assessment 

does not rule out potential effects (exceedances of the level of concern) based on the broad 

default assumptions, EPA then uses increasingly specific methods and exposure models to refine 

its estimated environmental concentrations. 

The results of the screening level risk assessments indicate that the RQs do not exceed the 

Agency’s LOC for terrestrial invertebrates (including pollinators), freshwater fish, aquatic-phase 

amphibians, estuarine/marine fish, freshwater invertebrates, or estuarine/marine invertebrates for 

either acute or chronic exposures. Acute RQs for aquatic plants and mammals, and chronic RQs 

for birds, reptiles, and terrestrial-phase amphibians also do not exceed the Agency’s LOC. The 

screening level assessment uses broad default assumptions to establish estimated environmental 

concentrations of particular pesticides. It does not make effects determinations related to any 

particular listed species. Instead, species-specific assessments are conducted for effects 

determinations. A more detailed description can be found in Section IV below.

For both cotton and soybeans, based on the proposed maximum application rates, the screening

level analysis indicates that risks for acute exposure to listed and non-listed birds, and listed and 

non-listed terrestrial dicot plant species, result in RQs that exceed the Agency’s LOCs. For 

soybeans, there is also a potential for direct adverse effects to birds and mammals from chronic 

exposure to the dicamba degradate DCSA. Though the rates are similar to those in currently 

registered dicamba pesticide products, there is potential for ecological concerns related to a 

potential increase in acres treated with dicamba products, resulting in additional acres with 

residues of DCSA in dicamba-tolerant soybeans. Before considering mitigation measures, EPA 

also found a potential for increased susceptibility of direct adverse effects to late season plants 

from spray drift.

While concern levels are exceeded in the screening level assessment, further refinement, as 

discussed below, suggest that risks are lower.

1. Risk to Birds

For birds, the screening level assessment indicated that the RQs exceeded the Agency’s LOCs on 

an acute basis for both soybean and cotton. More specifically, the screening level assessment 

found that the acute LOCs are exceeded for listed and non-listed birds, with a maximum acute 

dose-based RQ of 2.21 for small birds consuming short grass. Chronic LOCs were also exceeded 

for birds feeding on DCSA residues in dicamba-tolerant soybeans, with a maximum chronic 

dietary RQ of 1.7 for small birds consuming soybean forage/hay. 

The Agency’s screening level assessment employed residue estimates based on reasonable upper 

bound modeling assumptions for dicamba DGA residues on food items consumed by birds. 

These residue estimates have been developed for a variety of wildlife food items, and are based 

on measured residues from a large number of field trials on many pesticides. The Agency’s 

assessment also used the maximum labeled rate of the pesticide and the empirical maximum 

measured concentrations for DCSA residues in dicamba-tolerant soybeans and cotton plants to 

determine the RQ values. To represent a maximum, or “worst-case” estimate of risk, these highend exposure estimates for a variety of food items were compared, across a variety of body 

weights and sizes, to the most sensitive oral dose toxicity endpoint in order to generate RQs. 
20

Some of these RQs exceeded the LOC. While the LOCs were exceeded, further consideration of 

all lines of evidence shows that risks under more realistic use scenarios are expected to be lower.

For example, high-end dicamba residues compared to endpoints from toxicity studies using 

chemicals incorporated in the animal’s diet do not trigger concerns, suggesting that dicamba 

consumed in the diet may possibly be less available than assumed using dose-based 

exposures. Further, more frequently expected residues levels, such as mean or median estimates 

of exposure, would be lower by a factor of two or more, suggesting that residues are often not 

likely to trigger concerns for many food items. In addition, estimates of exposure in screening

level assessments are the maximum levels expected, and represent residues at the actual point of 

application, right on the field. The exposure analysis in this screening level risk assessment 

indicates that the transport of dicamba off-field by spray drift decreases with distance, suggesting 

that exposures to dicamba, and therefore associated risks, can be substantially lower for 

organisms with territories established at distance from the field. With this last line of evidence in 

mind, the draft pesticide label requires an in-field 110 to 220-foot buffer to further reduce off-site 

exposure for birds (buffer is discussed in more detail in the “Risk to Plants” section, below). 

Exposures to DCSA residues are only expected for birds feeding on dicamba-tolerant plants on 

the field, and are not expected off the field, regardless of spray drift of parent dicamba residues.

2. Risk to Mammals

For parent dicamba, none of the RQs for mammals exceed any of the Agency’s LOCs. Acute 

RQs range from <0.01 to 0.04 and chronic RQs range from 0.01 to 0.84. However, the screening 

level assessment using the maximum exposure values from empirical datasets for DCSA residues 

in dicamba-tolerant soybean resulted in exceedances of the chronic LOC for all size classes of 

mammals consuming soybean forage and hay, or consuming insects that had consumed soybean 

tissues with DCSA residues. These RQs range from 1.1 to 3.3. A screening level assessment 

using the maximum exposure values from empirical data for DCSA residues in dicamba-tolerant 

cotton did not result in exceedances of the chronic LOC for any mammal (chronic RQs ranged 

from <0.01 to 0.34).

The Agency’s screening level assessment employed residue estimates based on reasonable upper

bound modeling assumptions for dicamba residues, the maximum labeled rate of the pesticide, 

and the empirical maximum measured concentrations for DCSA residues in dicamba-tolerant 

soybeans and cotton plants to determine the RQ values. EPA further considered more realistic 

residue estimates and other lines of evidence, such as food preferences and foraging ranges 

relative to distance from the site of application. This analysis showed reduced concerns for 

adverse effects because larger mammals have more varied diets and larger home ranges where 

feeding is more likely to occur well away from treatment areas. 

Consideration of these lines of evidence also produces reduced risk estimates for small 

herbivorous mammals, due to reduced exposure, but does not reduce risk estimates for these 

organisms to the point that concern levels are not exceeded. As in the case for birds, the draft 

pesticide label requires an on-field 110 to 220-foot buffer in all directions to further reduce offsite exposure for mammals (buffer is discussed in more detail in the “Risk to Plants” section, 

below). Exposures to DCSA residues are only expected for mammals feeding on dicambatolerant plants on the field, and are not expected off the field, regardless of spray drift of parent 

dicamba residues.
21

3. Risk to Plants

For aquatic plants, the only RQ that would exceed an Agency LOC of 1.0 is for any listed nonvascular aquatic plants for the parent dicamba, with an RQ of 8.5. However, there are currently 

no listed non-vascular aquatic plants.

Dicamba exposure to terrestrial and semi-aquatic plants was estimated through modeling for 

plants residing near a use area that may be exposed via runoff and/or spray drift. Only a single 

application at the maximum rate for a particular use and compound-specific solubility 

information is considered, because it is assumed that for plants, toxic effects are likely to 

manifest shortly after the initial exposure, and that subsequent exposures do not contribute to the 

response. Hence, estimates are based on application rate, the solubility factor, and default 

assumptions of drift.

For a single application of dicamba at the maximum label rate for the proposed uses, the RQs 

exceeded the LOC (1.0) for terrestrial dicots due to spray drift, and for dicots in semi-aquatic 

areas due to runoff and spray drift. The RQs for dicots in semi-aquatic areas were 4.15 for nonlisted species and 7.58 for listed species. The RQs for spray drift were 19.49 for non-listed 

species of dicots and 38.31 for listed species of dicots. The RQs for dicots in dry areas were 0.49 

for non-listed species and 0.89 for listed species which are both less than the LOC for plants of 

1.0. 

Although the RQ analysis indicated there may be risks to plants from runoff and spray drift, 

studies conducted on the dicamba DGA formulation demonstrates that labeling restrictions will 

help to reduce spray drift off field. The registrant submitted additional studies for a refined spray 

drift analysis using the specific Tee Jet® TT11004 nozzles and the formulation in its application 

for registration. The analysis indicates that the dicamba product applied through the specific Tee 

Jet® TT11004 nozzle is protective of plants from exposures of the M1691 herbicide when an 

adequate buffer is incorporated between the application equipment and the edges of the treated 

field.

Additionally, to further mitigate against potential risks to plants from spray drift, the product 

labeling requires the use of 110-220 foot (depending on application rate) buffer between the last 

treated row and the closest edge of the field to be treated (in all directions). The Agency 

considered exposure to spray drift to be the principal risk issue associated with the proposed 

labeled use for all taxa. EPA considered a variety of lines of evidence, including past experience 

with other dicamba formulations and associated spray drift incident reporting. 

4. Synergism

EPA is aware that a common agricultural practice involves tank mixing of pesticides, resulting in 

the co-occurrence of chemical stressors to non-target plants including endangered species. This 

phenomenon has been described in academic research as well as patent application filings where 

the combined mixture is sometimes claimed to have enhanced activity or synergistic effects. In 

EPA’s risk assessments, the Agency uses GLP guideline studies to determine potential toxicity to 

plants, involving apical endpoints such as biomass and reproductive health. EPA believes this 

approach is very reliable for these purposes. However, at this time, the topic of synergy and 

multiple stressors is an uncertainty in assessing risk to non-target plants including endangered 
22

species. Therefore, EPA is proposing a tank mix prohibition on the M1691 label to address this 

uncertainty.

IV. Endangered Species for Dicamba Diglycolamine Salt (DGA)

Below is a summary of the endangered species assessments for dicamba (DGA). More detailed 

discussions can be found in the EPA documents titled, Addendum to Dicamba Diglycolamine 

Salt (DGA) Section 3 Risk Assessment: Refined Endangered Species Assessment for Proposed 

New Uses on Herbicide-Tolerant Soybean and Cotton in 16 states (Arkansas, Illinois, Iowa, 

Indiana, Kansas, Louisiana, Minnesota, Mississippi, Missouri, Nebraska, North Dakota, Ohio, 

Oklahoma, South Dakota, Tennessee, and Wisconsin); Addendum to Dicamba Diglycolamine 

(DGA) Salt Section 3 Risk Assessment: Endangered Species Effects Determinations for Dicamba 

DGA on Herbicide-Tolerant Cotton and Soybean in 7 U.S. States: AL, GA, KY, MI, NC, SC, and 

TX; and Addendum to Dicamba Diglycolamine (DGA) Salt Section 3 Risk Assessment: 

Endangered Species Effects Determinations for Dicamba DGA on Herbicide-Tolerant Cotton 

and Soy in 11 U.S. States: AZ, CO, DE, FL, MD, NM, NJ, NY, PA, VA and WV. These documents 

are in the docket for this proposed decision.

In the screening level risk assessment performed for the new application timing of dicamba 

(DGA) on genetically modified cotton and soybean to be tolerant to dicamba, EPA determined 

that direct concerns were unlikely (i.e. levels of concern were not exceeded) for mammals 

(acute) and (chronic- for cotton use only), birds, reptiles, and terrestrial-phase amphibians 

(chronic from parent dicamba or DCSA degradate from use on cotton), terrestrial insects, 

freshwater fish, aquatic-phase amphibians (acute and chronic), estuarine/marine fish (acute and 

chronic), freshwater invertebrates (acute and chronic), estuarine/marine invertebrates (acute and 

chronic), and aquatic plants (vascular and non-vascular). However, potential indirect effect risk 

concerns were identified for any species that have dependencies (e.g., food, shelter, and habitat) 

on mammals, birds, reptiles, terrestrial-phase amphibians, or terrestrial plants that are directly 

affected.

EPA has a specific process based on sound science that it follows when assessing risks to listed 

species for pesticides like dicamba that will be used on seeds that have been genetically modified 

to be tolerant to the pesticide. The Agency begins with a screening level assessment that 

includes a basic ecological risk assessment consistent with its 2004 Overview of the Ecological 

Risk Assessment Process document. [USEPA, 2004, available athttps://www.epa.gov/endangeredspecies/ecological-risk-assessment-process-under-endangered-species-act]. That assessment uses broad 

default assumptions to establish estimated environmental concentrations of particular pesticides. 

If the screening level assessment results in a determination that no levels of concern are 

exceeded EPA concludes its analysis. On the other hand, where the screening level assessment 

does not rule out potential effects (exceedances of the level of concern) based on the broad 

default assumptions, EPA then uses increasingly specific methods and exposure models to refine 

its estimated environmental exposures. At each step, EPA compares the more refined exposures 

to the toxicity of the pesticide active ingredient to determine whether the pesticide exceeds levels 

of concern established for listed aquatic and terrestrial species. EPA determines that there is “no 

effect” on listed species if, at any step in the screening level assessment, no levels of concern are 

exceeded. If, after performing all of the steps in the screening level assessment, a pesticide still 
23

exceeds the Agency’s levels of concern for listed species, EPA then conducts a species-specific 

refined assessment to make effects determinations for individual listed species. The refined 

assessment, unlike the screening level assessment, takes account of species’ habitats and 

behaviors to determine whether any listed species may be affected by use of the pesticide. 

The screening level ecological risk assessment generates a series of taxonomic (e.g., mammals, 

birds, fish, etc.) risk quotients (RQs) that are the ratio of estimated exposures to acute and 

chronic effects endpoints. These RQs are then compared to EPA established levels of concern 

(LOCs) to determine if risks to any taxonomic group are of concern. The LOCs address risks for 

both acute and chronic effects. Acute effects LOCs range from 0.05 for aquatic animals that are 

Federally-listed threatened or endangered species (listed species) to 0.5 for aquatic non-listed 

animal species and 0.1 to 0.5 for terrestrial animals for listed and non-listed species. The LOC 

for chronic effects for all animal taxa (listed and non-listed) is 1. Plant risks are handled in a 

similar manner, but with different toxicity thresholds (NOAEC/EC05 and EC25, respectively) 

used in RQ calculation for listed and non-listed species and an LOC of 1 used to interpret the 

RQ. As described above, if the screening level assessment shows that an RQ exceeds either the 

acute or chronic LOC, a concern for direct toxic effects is identified for that particular taxon and 

a species-specific assessment is necessary to make an effects determination. On the other hand, if 

RQs fall below the LOC, a no effect determination is identified for the corresponding taxon.

This registration for dicamba is being proposed for registration for use in the states of Alabama, 

Arkansas, Arizona, Colorado, Delaware, Florida, Georgia, Illinois, Indiana, Kansas, Kentucky, 

Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New Mexico, New 

Jersey, New York, North Carolina, North Dakota, Ohio, Oklahoma, Pennsylvania, South 

Carolina, South Dakota, Tennessee, Texas, Virginia, West Virginia, and Wisconsin. Additional 

states may be added to the labeling once an assessment of listed species is completed for any 

such state. 

Based on EPA’s LOCATES v.2.4.0 database and information from the U.S. Fish and Wildlife 

Service (USFWS), EPA identified the listed species that are inside the “action area” (area of 

concern where use of pesticide may result in exposure to endangered species) associated with the 

new cotton and soybean uses within a total of 30 states. 

The following criteria were used to assess listed species in the action area:

• For listed individuals inside the action area but not part of an affected taxa nor relying on 

the affected taxa for services involving food, shelter, biological mediated resources 

necessary for survival and reproduction, use of a pesticide would be determined to have 

“no effect.”

• For listed individuals outside the action area, use of a pesticide would be determined to 

have “no effect.” 

• Listed individuals inside the action area may either fall into the “no effect” or “may 

effect” categories depending upon their specific biological needs and circumstances of 

exposure. 
24

• Those that fall under the “may effect” category are found to be either “likely” or “not 

likely to be adversely affected.” This determination is made in consultation with the 

Services

• A “likely” or “not likely to adversely affect” determination is made using criteria that 

categorizes the effect as insignificant, highly uncertain, or wholly beneficial. 

Spray drift mitigation language including a 360 degree infield buffer (to varying length, 

depending on application rate) on the label is intended to limit off site transport of dicamba DGA 

through spray drift, as well as volatilization. Therefore, EPA expects that exposure will remain 

confined to the dicamba (DGA) treated field. Consequently, EPA concluded a no effect 

determination for all but 24 species originally identified as potentially at-risk (in the screening 

level assessment) because they are not expected to occur on cotton and soybean fields. 

The 24 remaining listed species that were not ruled out because their range contains areas that 

include treated fields were considered in more depth in EPA’s refined endangered species 

assessments. Species-specific biological information along with dicamba (DGA) use patterns 

were also considered. After utilizing processes such as refined modeling incorporating speciesspecific information and migration habits, EPA made a determination that exposure occurring on 

the field would have “may affects” (either "unlikely to adversely affect" or “likely to adversely 

affect” on 2 species (the Spring Creek Bladderpod and the Audubon Crested Caracara) in 2 

counties (Wilson county, TN and Palm Beach county, FL, respectively) within the States covered 

by this proposed decision. Furthermore, the Agency has concluded that the 2 species in question 

will not be of concern as the registrant has agreed to include on the final labeling a prohibition on 

application in both counties, thus mitigating any possible chance of exposure.

Additionally, the Agency considered the potential effects attributed to runoff. As refined 

modeling predictions indicate that expected exposures from runoff (sheet flow) are below the 

most sensitive toxicological endpoint thresholds, EPA’s analysis supports a “no effects” 

determination for runoff exposure for off-field listed plants for the proposed labeled use of 

dicamba DGA. Additionally, EPA is proposing to require rainfast mitigation on the label (“Do 

not irrigate treated fields for at least 24 hours after application of this product. Do not make 

application of this product if rain is expected in the next 24 hours.”) to protect against the risk of 

exposure to listed species off the treated field. 

V. Resistance Management

The emergence of herbicide resistant weeds is an increasing problem that has become a

significant issue to growers. This has led to a concern that the use of dicamba on geneticallymodified crops may result in over-reliance on dicamba and result in a larger number of resistant 

weeds. Currently, in certain areas of the United States there are populations of Kochia and 

prickly lettuce known to be resistant to dicamba. Kochia infests millions of acres of soybean and 

cotton and, in addition, glyphosate-resistant biotypes have been identified in Kansas and 

Nebraska.

In an effort to address these issues, EPA is proposing, as a term of registration, that Monsanto 

develop an Herbicide Resistance Management (HRM) plan that will promote herbicide 

resistance management efforts by growers, the registrant, and others. The plan mandates that 

Monsanto must investigate any reports of lack of performance. Dicamba users who experience a 
25

lack of performance can communicate directly with Monsanto by a toll free telephone number 

that is identified on the label to get advice on how to resolve any uncontrolled weeds. 

“Lack of performance” refers to inadequate weed control with various possible causes, including, 

but not limited to: application rate, stage of weed growth, environmental conditions, herbicide 

resistance, plugged nozzle, boom shut off, tank dilution, post-application weed flush, unexpected 

rainfall event, weed misidentification, etc. It can be challenging to distinguish emerging weed 

resistance from other causes at an early stage. Therefore, EPA has identified criteria that should 

be used to evaluate instances of “lack of performance” to determine if they do in fact constitute 

“likely herbicide resistance.” These “likely herbicide resistance” criteria are: (1) failure to 

control a weed species normally controlled by the herbicide at the dose applied, especially if 

control is achieved on adjacent weeds; or (2) a spreading patch of uncontrolled plants of a 

particular weed species; or (3) surviving plants mixed with controlled individuals of the same 

species (Norsworthy, et al., 2012). The identification of any of these criteria in the field indicates 

that “likely herbicide resistance” is present. The responsibilities of the registrant if “likely 

herbicide resistance” is found are discussed below. 

Researchers, extension specialists, growers, USDA, and other leaders involved with pest 

management all acknowledge the importance of scouting (e.g., monitoring the fields) in 

herbicide resistance management. For the proposed uses, the labeling states that fields should be 

scouted before application of dicamba to identify the weed species present as well as their stage 

of growth. Fields also should be scouted after each application to identify lack of performance 

that may be the early signs of resistance. Additionally, the labeling states that in the event that a 

user encounters lack of performance they should report this to Monsanto or its representative 

using the toll-free number identified on the label. The registrant must then evaluate the situation 

to determine if lack of performance is caused by resistance or likely resistance.

When a lack of performance is identified and reported to the registrant, Monsanto or its 

representative must investigate and conduct a site visit if needed to evaluate the lack of 

performance using decision criteria identified by leading weed science experts in order to 

determine if “likely herbicide resistance” is present (also termed “possible resistance” by 

Norsworthy[i], et al., 2012). A report of lack of herbicide performance to Monsanto will be the 

trigger to start this investigation.

When Monsanto or its representative applies the Norsworthy, et al., criteria cited above, and 

likely herbicide resistance is identified, Monsanto must proactively engage with the grower to 

control and contain likely resistant weeds in the infested area. This may be accomplished by retreating with an herbicide or using mechanical control methods. After implementing these 

measures, Monsanto must follow-up with the growers, with the growers’ permission, to 

determine if the likely resistant weeds have been controlled. Monsanto must also annually report 

to EPA findings of likely herbicide resistance. In addition, prior to implementing control 

measures, Monsanto must make best efforts to obtain samples of the likely herbicide resistant 

weeds and/or seeds, and as soon as practicable, laboratory or greenhouse testing must be initiated 

in order to confirm whether resistance is the reason for the lack of herbicide efficacy.

Beginning January 15th, 2018, on or before January 15th of each year, Monsanto must submit 

annual summary reports to EPA. These reports must include a summary of the number of 

instances of likely and confirmed resistance by weed species, crop, county and state. These 

reports will also summarize the status of laboratory or greenhouse testing for resistance. The 
26

annual reports will also address the disposition of incidents of likely or confirmed resistance 

reported in previous years.

Monsanto must report annually any inability to control likely resistant weeds to relevant 

stakeholders. To accomplish this, Monsanto must establish a website to facilitate delivery of 

resistance information to users.

Several best management practices that are designed to help users avoid initial occurrences of 

weed resistance appear on the proposed dicamba product label listed under the Herbicide 

Resistance Management heading of the label. These practices are discussed in Section VIII.B.3 

of this document.

Refer to Section VIII.C below for EPA’s terms of registration to address the issue of weed 

resistance.

VI. Response to Comments

The Agency received 11 comments in response to the Notice of Receipt (Docket Number: EPAHQ-OPP-2010-0496) for the application to register the use of dicamba on genetically-modified 

soybeans and no comments in response to the Notice of Receipt (Docket Number: EPA-HQOPP-2012-0841) for the application to register the use of dicamba on genetically-modified 

cotton. The majority of comments expressed concern (e.g., spray drift and volatilization) and 

requested that the Agency deny the proposed registration. The EPA welcomes input from the 

public during the decision process when registering pesticides, and is committed to thoroughly 

evaluating and mitigating any potential risks from registered pesticides, consistent with 

applicable statutory standards. EPA considered the public comments received in this regulatory 

decision.

The commenters focused on spray drift and volatilization concerns affecting non-target 

plants. The Agency has evaluated the risks regarding the potential drift of pesticides to sensitive 

crops and other non-target plants that may be adjacent to treatment areas. Specific label 

directions and restrictions have been proposed to protect from off-target movement of this 

pesticide product. Specifically, the proposed registration decision requires a 110-220 foot buffer 

between the treated area and edge of the field in all directions. These buffers are expected to 

keep spray drift from moving beyond the edge of the crop field to be treated as well as reduce the 

concern for volatility. In addition, the label will specify a spray nozzle and pressure combination 

that is expected to reduce drift of the herbicide to distances within these buffers. The proposed 

regulatory decision also specifies that this product cannot be applied when the wind speed is over 

15 mph, and no aerial application is permitted. Label language regarding spray volume, 

equipment ground speed, and spray boom height is intended to further protect against off-target 

drift. More details on EPA’s and Monsanto’s efforts to minimize effects to non-target plant 

species can be found in Section VIII.B.4 of this document.

Commenters also expressed concerns that weeds resistant to dicamba will become more 

prevalent as a result of this proposed use. Weed resistance is an increasing problem that has 

become a significant economic issue to growers. In an effort to address this concern and to 

prevent new weed resistance from happening, while giving growers another essential tool in their 

integrated pest management programs, Monsanto must put into place a stewardship program to 

promote responsible use of the proposed product in order to minimize the potential for increased 
27

levels of weed resistance. This plan is discussed in detail in Section V and Section VIII.B.3 of 

this document.

VII. Benefits

Growers throughout the United States have experienced yield and economic losses due to weeds 

developing resistance to the herbicide glyphosate and other heavily used herbicides. The need for 

additional tools to manage these resistant weeds has become important as resistance to both 

glyphosate and other herbicides has become a significant financial, production and pest 

managment issue for many cotton and soybean growers. Weeds such as marestail, giant ragweed, 

common waterhemp, and Palmer amaranth can be difficult to control during the crop growing 

season. urrent registered uses of dicamba only allow for pre-plant application and post-harvest 

application in cotton for conventional or conservation tillage systems. Similarly, the currently 

registered use of dicamba on soybeans only allows for preplant application along with a preharvest broadcast or spot treatment application. New postemergence uses of dicamba would 

expand weed management options on genetically-modified cotton and soybeans by providing an 

additional mechanism of action during the growing season. Dicamba used during the season 

would target new flushes of weeds, thereby reducing populations of these weeds and particularly 

would help reduce seed banks. Postemergence use of dicamba will expand options for weed 

control in cotton and soybeans and enable control of broadleaf weeds, including glyphosateresistant biotypes.

VIII. Proposed Registration Decision 

In accordance with FIFRA, EPA only registers a pesticide when it can ensure that it will not 

cause unreasonable adverse effects on man or the environment, taking into account the 

economic, social, and environmental costs and benefits of the use of the pesticide. Under FIFRA, 

EPA is charged with balancing the uncertainties and risks posed by a pesticide against its 

benefits. EPA must determine if the benefits in light of its use outweigh the risks in order for the 

Agency to register a pesticide.

In the case for the proposed use of dicamba on dicamba-tolerant soybeans and cotton, and in 

consideration of all best available data and assessment methods, EPA believes this proposed 

decision to register these uses meets the requirements of FIFRA. The database submitted to 

support the assessment of human health risk is sufficient for a full hazard evaluation and is 

considered adequate to evaluate risks to infants and children. The Agency has not identified any 

risks of concern in regards to human health, including all population subgroups, or for 

occupational handlers. 

In terms of ecological risk, some levels of concern were exceeded for certain birds and mammals 

that may be in the fields that would be treated. The Agency notes that these are very conservative 

risk estimates using screening level (worst case) assumptions, and that they most likely do not 

apply to the majority of the birds and mammals that are outside of the treatment area. For 

example, it is assumed that animals would forage for food exclusively in the treated area 

consuming only the treated crop, neither of which is likely to be true. Additionally, the 

protections afforded by the labeling, such as the requirement of infield buffers, would reduce the 

likelihood of spray drift and volatilization that could affect organisms located beyond the treated 
28

field. Because of these additional restrictions, EPA expects the proposed uses to have less 

environmental impact than other currently registered products that do not require the same 

buffers. It is also noted that, if further refinements that included more realistic exposure scenarios 

were conducted, these risks would likely fall below the Agency’s levels of concern.

On the benefits side of the analysis, use of dicamba on dicamba-tolerant soybeans and cotton is 

expected become an important part of a resistance management strategy for these crops. 

Soybeans and cotton are extremely important agricultural commodities in the United States and 

the world. According to the USDA’s National Agricultural Statistics Service, soybeans are 

grown on approximately 85 million acres and cotton is grown on approximately 9 million acres. 

USDA’s Economic Research Service describes soybeans as the world's largest source of animal 

protein feed and the second largest source of vegetable oil, and describes cotton as one of the 

most important textile fibers in the world, accounting for around 35 percent of total world fiber 

use. The United States is the world’s leading soybean producer and exporter, and together with 

China and India provide two-thirds of the world's cotton. USDA estimates the gross value of 

soybean production at approximately 48 billion dollars in the United States, and soybean is 

grown throughout the United States with more than 80 percent of U.S. soybean acreage

concentrated in the upper Midwest. The gross cotton production is estimated by USDA at over 6 

billion dollars in the United States, and is grown in 17 states stretching across the southern half 

of the United States. However, resistance to glyphosate, the current market leader in soybeans 

and cotton, is having severe economic consequences in soybean and cotton production. The 

Weed Science Society of America and other weed control experts warn that the problem of 

glyphosate resistance is increasing, and that significant economic consequences will continue to 

increase without effective alternatives for weed control.

Consequentially, use of dicamba on dicamba-tolerant soybeans and cotton would be beneficial as 

it provides an effective tool to treat especially noxious weeds such as marestail, giant ragweed, 

common waterhemp, and Palmer amaranth, including glyphosate-resistant biotypes that threaten 

soybean and cotton production today. By adding an effective tool to combat glyphosate-resistant 

weeds, dicamba could help reduce this difficult weed pressure and aid significantly in 

production, reducing economic losses to soybean and cotton growers. In addition, effective 

treatment of glyphosate-resistant weeds can help control the spread of resistance. And, as stated 

previously, using dicamba for these uses according to the proposed labeling restrictions will 

include protections such as in-field buffers, best practice requirements for drift management and 

application techniques, and active resistance management stewardship of weed populations.

After weighing all the risks of concern against the benefits of the proposed uses, EPA finds that 

when the proposed mitigation measures are applied, the risks that may remain are minimal, if 

they exist at all, while the benefits are potentially great. Therefore, the benefits outweigh the 

risks and registering these uses will not generally cause unreasonable adverse effects on human 

health or the environment during the 5-year time limited registration being proposed (a 5-year 

registration is proposed so that any unexpected weed resistance issues that may result from the 

proposed uses can be addressed before granting an extension or EPA can allow the registration to 

terminate if necessary). EPA believes that the available data and scientific assessments as well as 

the overall considerations for benefits for weed management in these important crops support a 

FIFRA Section 3(c)(5) registration finding for the proposed uses.
29

A. Data Requirements

There are no outstanding data requirements required to support the registration of this action.

However, data may be required in connection with registration review activities for dicamba. 

Those requirements would be generic to dicamba uses and products in general and would be 

handled in accordance with the registration review process.

B. Labeling Requirements

The following labeling is included in the proposed supplemental labels unless otherwise noted 

below.

1. Worker Protection (Although the following Worker Protection labeling applies to the 

proposed new uses, it is not included in the proposed supplemental labeling. This 

labeling can be found in the previously accepted master labeling that was accepted by the 

Agency on September 18, 2013 for this product.)

Do not apply this product in a way that will contact workers or other persons, either 

directly or through drift. Only protected handlers may be in the area during application. 

For any requirements specific to your state or tribe, consult the agency responsible for 

pesticide regulation. 

Do not enter or allow worker entry into treated areas during the restricted entry interval 

(REI) of 24 hours.

PPE required for mixers, loaders, applicators and other handlers is: 

• Long-sleeved shirt and long pants 

• Chemical-resistant gloves

• Shoes plus socks 

PPE required for early entry to treated areas that is permitted under the Worker Protection 

Standard and that involves contact with anything that has been treated, such as plants, soil, 

or water, is: 

• Coveralls worn over short sleeved shirt and short pants

• Chemical-resistant footwear plus socks

• Chemical-resistant gloves made of any waterproof material

• Chemical-resistant headgear for overhead exposure

• Protective eyewear

2. Environmental Hazards (Although the following Environmental Hazards labeling 

applies to the proposed new uses, it is not included in the proposed supplemental labeling. 

This labeling can be found in the previously accepted master labeling that was accepted 

by the Agency on September 18, 2013 for this product.)
30

Do not apply directly to water, to areas where surface water is present, or to intertidal areas 

below the mean high water mark. Do not contaminate water when disposing of equipment 

washwaters or rinsate. Apply this product only as directed on the label.

This chemical is known to leach through soil into ground water under certain conditions as 

a result of agricultural use. Use of this chemical in areas where soils are permeable, 

particularly where the water table is shallow, may result in ground water contamination.

3. Resistance Management

To aid in the prevention of developing weeds resistant to this product, the following steps 

should be followed: 

• Scout fields before application to ensure herbicides and rates will be appropriate for the 

weed species and weed sizes present.

• Apply full rates of M1691TM for the most difficult to control weed in the field at the 

specified time (correct weed size) to minimize weed escapes.

• Scout fields after application to detect weed escapes or shifts in weed species.

• Report any incidence of non-performance of this product against a particular weed 

species to your Monsanto retailer, representative or call XXXXXXX.

• If resistance is suspected, treat weed escapes with an herbicide having a mode of action 

other than Group 4 and/or use non-chemical methods to remove escapes, as practical, 

with the goal of preventing further seed production.

Additionally, users should follow as many of the following herbicide resistance 

management practices as practicable:

• Use a broad spectrum soil-applied herbicide with other modes of action as a foundation 

in a weed control program.

• Utilize sequential applications of herbicides with alternative modes of action.

• Rotate the use of this product with non-Group 4 herbicides.

• Incorporate non-chemical weed control practices, such as mechanical cultivation, crop 

rotation, cover crops and weed-free crop seeds, as part of an integrated weed control 

program.

• Thoroughly clean plant residues from equipment before leaving fields suspected to 

contain resistant weeds.

• Avoid using more than two applications of dicamba and any other Group 4 herbicides 

within a single growing season unless in conjunction with another mode of action 

herbicide with overlapping spectrum.

• Manage weeds in and around fields, during and after harvest to reduce weed seed 

production.
31

4. Spray Drift Management

Nozzle type:

Use the Tee Jet® TTI11004 nozzle with a maximum operating pressure of 63 psi when 

applying M1691 Herbicide. Do not use any other nozzle and pressure combination not 

specifically allowed by this label.

Spray Volume:

Apply this product in a minimum of 10 gallons of spray solution per acre. Use a higher 

spray volume when treating dense vegetation. 

Equipment Ground Speed:

Select a ground speed that will deliver the desired spray volume while maintaining the 

desired spray pressure, but do not exceed a ground speed of 15 miles per hour. Slower 

speeds generally result in better spray coverage and deposition on the target area.

Spray boom Height: 

Spray at the appropriate boom height based on nozzle selection and nozzle spacing, but 

do not exceed a boom height of 24 inches above target pest or crop canopy. Set boom to 

lowest effective height over the target pest or crop canopy based on equipment 

manufacturer’s directions. Automated boom height controllers are recommended with 

large booms to better maintain optimum nozzle to canopy height. 

Temperature and Humidity:

When making applications in low relative humidity, set up equipment to produce larger

droplets to compensate for evaporation. Larger droplets have a lower surface to volume 

ratio and are impacted less by temperature and humidity. Droplet evaporation is most 

severe when conditions are both hot and dry.

Temperature Inversions:

Applications should not occur during a local, low level temperature inversion because 

drift potential is high. Temperature inversions restrict vertical air mixing, which causes 

small suspended droplets to remain in a concentrated cloud. This cloud can move in 

unpredictable directions due to the light variable winds common during 

inversions. Temperature inversions are characterized by increasing temperatures with 

altitude and are common on nights with limited cloud cover and light to no wind. They 

begin to form as the sun sets and often continue into the morning. Their presence can be 

indicated by ground fog; however, if fog is not present, inversions can also be identified 

by the movement of the smoke from a ground source generator. Smoke that layers and 

moves laterally in a concentrated cloud (under low wind conditions) indicates an 

inversion, while smoke that moves upward and rapidly dissipates indicates good vertical 
32

air mixing. The inversion will dissipate with increased winds (above 3 MPH) or at 

sunrise when the surface air begins to warm (generally 3°F from morning low).

Wind Speed:

Drift potential is lowest between wind speeds of 3 to 10 miles per hour. Do not apply at 

wind speeds greater than 15 mph. A chart is included in the product label that lists the 

appropriate wind speeds and application conditions and restrictions. 

5. Protection of Sensitive Areas:

a. Buffer

Maintain a 110-foot buffer (when applying 16 fl oz of this product per acre), or a 220-

foot buffer (when applying 32 fl oz of this product per acre) between the treated area and 

the edge of the field in all directions.

b. Susceptible Plants:

Do not apply under circumstances where spray drift may occur to food, forage, or other 

plantings that might be damaged or the crops thereof rendered unfit for sale, use or 

consumption. Do not allow contact of herbicide with foliage, green stems, exposed nonwoody roots of crops, and desirable plants, including beans, cotton, flowers, fruit trees, 

grapes, ornamentals, peas, potato, soybean, sunflower, tobacco, tomato, and other 

broadleaf plants, because severe injury or destruction may result, including plants in a 

greenhouse. Small amounts of spray drift that may not be visible may injure susceptible 

broadleaf plants. 

Applicators are required to ensure that they are aware of the proximity to sensitive areas, 

and to avoid potential adverse effects from off-target movement of M1691 Herbicide. 

Before making an application, the applicator must survey the application site for 

neighboring sensitive areas prior to application. The applicator should also consult 

sensitive crop registries for locating sensitive areas where available.

Failure to follow the requirements in this label could result in severe injury or destruction 

to desirable sensitive broadleaf crops and trees when contacting their roots, stems or 

foliage.

Specifically, commercially grown tomatoes and other fruiting vegetables (EPA crop 

group 8), cucurbits (EPA crop group 9), and grapes are sensitive to dicamba. In order to 

prevent unintended damage from any drift of this product, do not apply this product when 

the wind is blowing towards adjacent commercially grown sensitive crops. 

6. Application Restrictions: 

• Do not apply this product aerially. 

• Do not tank mix any other herbicides with M1691 Herbicide.

• Do not make an application of the product if rain is expected in the next 24 hours.
33

• The maximum combined quantity of this product that may be applied for all preplant, 

at-planting, and preemergence applications is 32 fluid ounces (1.0 lb a.e. dicamba) per 

acre per season for both cotton and soybeans. 

• The maximum application rate for a single, preplant, at-planting, or preemergence 

application must not exceed 32 fluid ounces (1.0 lb a.e. dicamba) per acre for both 

cotton and soybeans. 

• The combined total application rate from crop emergence up to R1 must not exceed 32 

fluid ounces (1.0 lb a.e. dicamba) per acre for soybeans.

• The combined total application rate from crop emergence up to 7 days pre-harvest must 

not exceed 64 fluid ounce (2.0lb a.e dicamba) per acre for cotton.

• All applications for both cotton and soybeans must not exceed 64 fluid ounces (2.0 lb 

a.e dicamba) per acre.

C. Registration Terms

EPA has determined that certain registration terms are needed to ensure that likely weed 

resistance as discussed in section V will be adequately addressed. EPA believes that it is 

important to address likely weed resistance and not wait until confirmation that resistance has 

been found. EPA is basing the proposed registration terms on a list of criteria, presented in 

the peer-reviewed publication, Norsworthy, et al., “Reducing the Risks of Herbicide 

Resistance: Best Management Practices and Recommendations,” Weed Science 2012 Special 

Issue: 31–62 (Norsworthy criteria). 

1. Herbicide Resistance Management (HRM) Plan 

Monsanto must have an Herbicide Resistance Management (HRM) Plan for M1691 

Herbicide developed and approved by EPA before a final registration can be issued. The 

HRM Plan must focus on educating growers on the appropriate use of the M1691 

Herbicide and the associated dicamba-tolerant seeds. EPA is requiring that the HRM 

Plan include the following measures that will reduce the potential for the development 

of weed resistance.

a. Investigation

Monsanto or its representative must investigate reports of lack of herbicide efficacy as 

reported by users following “scouting.” When investigating any reports of lack of 

herbicide efficacy, Monsanto or its representative must make an effort to evaluate the 

field for “likely resistance” by applying the “Norsworthy criteria.”

b. Remediation

If “likely resistance” is found, Monsanto must engage with the grower to control and 

prevent the spread of likely resistant weeds in the affected area. Additionally, Monsanto 

must collect material, if possible, for further testing. Monsanto must provide the grower 

with specific information and recommendations to control and contain likely resistant 

weeds, including retreatment and/or other nonchemical controls, as appropriate, and if 
34

requested by the grower, Monsanto will assist the grower in implementing those 

additional weed control measures.

c. Annual Reporting of Herbicide Resistance to EPA

Monsanto must submit annual summary reports to EPA that include a summary of the 

number of instances of likely and confirmed weed resistance by weed species, crop, 

county and state. The annual reports must include summaries of the status of laboratory 

or greenhouse testing for resistance. The annual reports will also address the disposition 

of incidents of likely or confirmed resistance reported in previous years. These reports 

will not replace or supplement adverse effects reporting required under FIFRA § 

6(a)(2).

d. Reporting of Likely Resistance to other Interested Parties

Monsanto must inform growers and other stakeholders of cases of likely resistance that 

are not resolved by the application of additional weed control measures. 

e. Education

Monsanto must develop an education program that will provide growers with the best 

available information on herbicide resistance management.

 2. EPA’s Continued Control over the Registration 

Because the issue of weed resistance is an extremely important issue to keep under control 

and can be very fast moving, this registration will expire 5 years from the date of the 

registration issuance, unless this term is removed or modified by EPA. At the end of 5 

years, EPA can work to address any unexpected weed resistance issues that may result 

from the proposed uses before granting an extension or allow the registration to terminate 

if necessary.

 3. Geographic Limitation on Use of Dicamba M1691 Herbicide

EPA is proposing to issue this registration only to be sold and used in Alabama, Arizona, 

Arkansas, Colorado, Delaware, Florida, Georgia, Illinois, Iowa, Indiana, Kansas, 

Kentucky, Louisiana, Maryland, Michigan, Minnesota, Mississippi, Missouri, Nebraska, 

New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, 

Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Virginia, West Virginia, 

and Wisconsin.

[i] Norsworthy, J. K., Ward, S. M., Shaw, D. R., Llewellyn, R. S., Nichols, R. L., Webster, T. M., Bradley, K. W., Frisvold, 

G., Powles, S. B., Burgos, N. R., Witt, W. W., Barrett, M. 2012. Reducing the risks of herbicide resistance: Best 

Managment Practices and Recommendations. Weed Science Special Issue: 31-62. 

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