UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

APR J 9 2014 

MEMORANDUM 

OFFICE OF CHEMICAL SAFETY 

AND POUliTION PREVENTION 

SUBJECT: BEAD Chemical Profile (BCP) for Registration Review: Diclofop-methyl 

(110902) 

FROM: Bill Phillips, Ph.D., Agronomis~ Biological Analysis Branch ~ . / 

THRU: 

TO: 

Jihad Alsadek, Ph.D., Economist 7:/t.uJ 1ft "' ~~ 

Science Information and Analysis Branch 

Michelle Ranville, Economist { H rrYJ 

Economic Analysis Branch V "--'t......AJ 

Biological and Economic Analysis Division (7503P) 

Arnet Jones, Chief 

Biological Analysis Branch 

Diann Sims, Chief Af~ ~ r /}.~,...,.J/ Science Information and An9)alys1s Branch:Q 

Timothy Kiely, Chief \}A L 

Economic Analysis Branch \ 

Biological and Economic An y s Division (7 3P) 

Steven Snyderman, Chemical Review Manager 

Risk Management and Implementation Branch 3 

Pesticide Re-evaluation Division (7508P) 

Peer Review Panel date: Apri116, 2014 

SUMMARY 

Diclofop-methyl was first registered as an herbicide in the U.S. in 1982 (USEPA, 2000) to 

control annual grasses in wheat and barley as well as in turfgrass. This herbicide is in the Weed 

Science Society of America group one, a member of the aryloxyphenoxy propionate herbicide 

family, and is applied both preemergence and postemergence. During the period covering 2008 
to 2012, 91% of the total pounds of diclofop-methyl was applied in winter wheat. However, 

based on current weed resistance issues as well as the decline in overall usage, BEAD is unable 

to determine whether diclofop-methyl plays an important role in pest management for winter 

wheat production. 

Based on private market usage data from 1998-2012, usage averaged approximately 144,000 

pounds active ingredient (a.i.) applied annually on approximately 236,000 acres treated. The 

average a.i. rate over this time period was 0.610 pounds a.i. /acre. Available non-agricultural 

usage data for diclofop-methyl is limited and dated. 

INTRODUCTION 

The Biological and Economic Analysis Division (BEAD) Chemical Profile (BCP) provides an 

overview of the pest management roles and quantitative usage information for diclofop-methyl. 

The BCP includes summaries of previous BEAD products and available public and/or private 

use and usage data for diclofop-methyl to describe the role of this chemical in pest management. 

Information provided in this BCP may be used by stakeholders (e.g., users and registrants), OPP 

risk assessors, OPP risk manag_ers, and the general public during the Registration Review process 

of this chemical. 

USE SITES 

Agricultural Use Sites 

Diclofop-methyl registered agricultural use sites are barley and wheat. 

Non-agricultural Use Sites 

Diclofop-methyl registered non-agricultural use sites are golf courses and roadsides. 

FORMULATIONS AND APPLICATION METHODS 

Diclofop-methyl formulations include emulsifiable concentrate and liquid. Diclofop-methyl is 

applied by commercial sprayer spot treatment and via broadcast application with hose end 

sprayer. 

HISTORY OF DICLOFOP-METHYL and BEAD PRODUCTS 

Diclofop-methyl is an herbicide registered for use in the U.S. since 1982. A Screening Level 

Usage Analysis (SLUA) was prepared by BEAD for this chemical in 2014 that provides national 

level poundage applied by active ingredient (a.i.) and percent crop treated (PCT) data for barley 

and wheat. Both crops have less than one percent crop treated (PCT) with diclofop-methyl 

2 
(EPA, 2014). The relatively low PCT on barley and wheat indicate a low level of reliance on 

diclofop-methyl to control weeds in these crops. 

A search of the BEAD data base for previous BEAD products for diclofop-methyl indicates that 

there have not been any benefits assessments or Section 18 analyses prepared for this chemical. 

A search ofthe OPP Section 18 database indicates there have been no requests for emergency 

exemptions to use diclofop-methyl. The absence of these assessments and requests, however, 

does not indicate that the chemical has no benefits to users. 

USAGE 

Agricultural Usage 

Based on private market usage data from 1998-2012, usage averaged approximately144, 000 

pounds active ingredient (a.i.) applied annually on approximately 236,000 acres treated. The 

average a.i. rate over this time period was 0.610 pounds a.i. /acre. Figure 1 presents diclofopmethyl usage in pounds a.i. over the 1998-2012 time frame. Figure 2 presents total area treated 

in acres over the same time frame (Proprietary Data, 1998-2012). 

800,000 

0 0'1 0 0'1 0 0'1 0 .-< N 

..... 

0 

0 

N 

N 

8 

N 

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0 

0 

N 

g 

0 

N 

Lll 

~ 

Year 

0.0 

0 

0 

N 

f' 

0 

0 

N 

co 

8 

N 

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N 

~ 0 

N 

FIGURE 1. Diclofop-methyl Usage in Pounds Active Ingredient, 1998-2012 

Source: Proprietary Data, 1998-2012 

N 

..... 

0 

N 

3 
1,300,000 

0 00 0'1 0 .... N m -t 11'1 1.0 r-- 00 0'1 0'1 0 0 0 0 0 0 0 0 0 0'1 0'1 0 0 0 0 0 0 0 0 0 .... .... N N N N N N N N N 

Year 

FIGURE 2. Diclofop-methyl Total Area Treated in Acres, 1998-2012 

Source: Proprietary Data, 1998-2012 

0'1 0 .... N 0 .... .... .... 0 0 0 0 N N N N 

--- -

Table 1. Crops with Highest :Use of Diclofop-methyl in Two Time Periods, Percent of Total 

Lbs. Applied {2003-2007 and 2008-2012) 

2003-2007 2008-2012 

Average Annual = 236,000 lbs/yr Average Annual= 27,000 lbs/yr 

Crop %Lbs Crop %Lbs 

Winter Wheat 93% Winter Wheat 91% 

Spring Wheat 4% Spring Wheat 7% 

Barley 3% Barley 2% 

Source: Proprietary Data, 1998 -2012. 

Table 2. States with Highest Use of Diclofop-methyl in Two Time Periods, Percent of Total 

Lbs. Applied (2003-2007 and 2008-2012) 

2003-2007 2008-2012 

Average Annual= 236,000 lbs/yr Average Annual= 27,000 lbs/yr 

State %Lbs State %Lbs 

North Carolina 31% North Carolina 61% 

Arkansas 14% Arkansas 20% 

Tennessee 13% North Dakota 7% 

Oregon 11 Tennessee 5% 

Source: Proprietary Data, 1998 -2012 

The major agricultural use of diclofop-methyl in both the 2003-2007 and 2008-2012 time frames 

was on winter wheat (93% of total pounds applied in 2003-2007 and 91% of total pounds applied 

in 2008-2012) followed by spring wheat (4%) and barley (3%) in 2003-2007, and (7% for spring 

4 
wheat and 2% for barley) during the 2008-2012 time frame. Usage has decreased on winter 

wheat and barley and increased on spring wheat in the most recent 2008-2012 time frame. 

Application Rates 

The average a.i. rate for the top crops in terms of pounds a.i. applied was the highest for spring 

wheat at 0.566lbs a.i./acre and the lowest for winter wheat at 0.499lbs a.i./acre as shown in 

Table 3. 

T a e bl 3 . n· IC I o fi op-met hI tyl U se on T C op rops: A verage A I . . Ra te, 2008 -2012 

Crop Average Annual Average Annual A vg. Annual A.I. 

Pounds Applied Total Acres Treated* Rate Obs a.iJacres) 

Winter Wheat 73,925 147,972 0.499 

Spring Wheat 5,524 9,757 0.566 

Barley 1,434 2,550 0.562 

*Total Acres Treated sums all acres treated for a crop, mcludmg those acres that receive multiple treatments. 

Source: Proprietary Data, 2008 -2012 

Non-Agricultural Usage 

There was minimal use of diclofop-methyl on turf and ornamentals in the most recent year that 

data was available, less than ten pounds active ingredient (Proprietary Data, 2012). 

Geographic Distribution ofDiclofop-methyl Use 

Figure 3 displays the average usage intensity of diclofop-methyl for the years 2008-2012. The 

highest usage intensity occurred in North Carolina and Arkansas followed by Virginia and North 

Carolina. 

5 
Pounds Active Ingredient 

per 1,000 Crop Acres Grown 

c:::JNoOata 

c:::J <OD9 

o o.09-0.17 

. 0.18-0.33 

- >0.33 

FIGURE 3. Diclofop-methyl Usage Intensity by State, 2008-2012 

Source: Proprietary Data, 2008-2012 

BIOLOGICAL ASPECTS RELEVANT TO DICLOFOP-METHYL 

Diclofop-methyl is an herbicide in the Weed Science Society of America group one and is a 

member of the aryloxyphenoxy propionate herbicide family. This herbicide has the mechanism 

of action of inhibiting the acetyl CoA carboxylase (ACCase) enzyme. Diclofop-methyl is used 

both preemergence and postemergence to control annual grasses in agronomic crops such as 

barley and wheat. In addition, this herbicide can be used to control some grass weeds in 

turf grass. 

ROLE OF DICLOFOP-METHYL IN PEST MANAGEMENT 

Overall, the use of diclofop-methyl has been decreasing since 1998. Based on the total amount 

of the herbicide that was applied between the years of 2008 and 2012, nearly all of the diclofop 

applied was in winter wheat (91% ), with most of the herbicide applied in Arkansas (20%) and 

North Carolina (61 %). 

When applied in winter wheat, diclofop-methyl is used primarily to control ryegrass weed 

species. Research focused on the efficacy of diclofop-methyl in North Carolina found that this 

herbicide provides excellent control ofryegrass (NCSCE, 2013). However, ryegrass populations 

resistant to diclofop are becoming more widespread. The increase in the resistant ryegrass 

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population over the years, may explain some of the decrease in diclofop-methyl use. Based on 

the resistance issue and the decline in usage, BEAD is unable to determine whether diclofopmethyl plays an important role in pest management for winter wheat production. 

DATA NEEDS 

The Agency currently does not have important information on diclofop-methyl. Obtaining the 

following information may improve future assessments conducted by the Agency related to the 

use and importance of diclofop-methyl: 

Usage information (e.g., acres treated, lbs applied, application rates, target pests) for nonagricultural uses 

Information regarding the importance of diclofop-methyl for pest management in any of 

the registered uses. 

REFERENCES 

EPA. 2000. Reregistration Eligibility Decision (RED) Diclofop-methyl. Available at: 

http://www.epa.gov/oppOOOO l/chem search/reg actions/reregistration/red PC110902 1-Sep-OO.pdf · 

EPA. 2014. Diclofop-methyl (110902) Screening Level Usage Analysis (SLUA). Biological and 

Economic Analysis Division. March 24,2014. 

Proprietary Data. 1998-2012. 

North Carolina State Cooperative Extension (NCSCE). 2013. Herbicide Efficacy on Most 

Common Weeds in North Carolina Winter Wheat. Available at: 

http:/ /www.ces.ncsu.edu/wp-content/uploads/20 13/ 12/Herbicide-Efficacy-. pdf. Accessed 

April2014. 

USDA, 2006-2010. NASS Crop Reporting Districts (shape file ofCRDs). Available at: 

http://www .ers. usda. gov /briefing/arms/resourceregions/resourceregions.htm#nass. 

USDA, 2006-2010. NASS Crop Reporting Districts. Online: 

http://www.nass.usda.gov/Data and Statistics/County Data Files/Frequently Asked Q 

uestions/county list.txt 

USDA, 2007. Census of Agriculture. Online: 

http://www .agcensus. usda. gov /Publications/2007 /index.asp. 

7 
APPENDIX A 

The map included herein primarily for the use of the risk assessors in the Environmental Fate and · 

Effects Division. The map provides a very broad geographical view of the amount (in pounds) 

ofthe active ingredient applied per 1,000 acres of"land in farms." These data are included in the 

maps because risk assessors are interested in the amount of a pesticide used across farmland. 

Because ofthe definition of Land in Farms, as discussed below, the calculated values presented 

in the map are not equivalent t~ an application rate (lbs a.i. I A). 

The data used to make these maps have many limitations. Any interpretation of the maps should 

consider the underlying data and the associated limitations carefully. 

The smallest areas shown on the maps within each state are Crop Reporting Districts (CRD). 

CRDs are defined by USDA and each consists of multiple counties that have similar soils, 

growing conditions, and farming practices. The CRDs within many states have roughly the same 

area. Because it is not feasible-to conduct an agricultural survey that samples every county in the 

United States, the use of CRDs allow for a sample to be collected that represent a much larger 

area with relatively homogeneous agricultural characteristics. 

The numerator (annual average pounds applied) is based on private market surveys of pesticide 

use in agriculture averaged over the last five years (Proprietary Data, 2008-2012). These surveys 

cover about 60 crops and are targeted in states that produce the majority of the crop. Although 

the surveys capture most of the use of a particular active ingredient in agriculture, there are 

several limitations to these su.rVeys. 

• States with minor production of a surveyed crop are not sampled 

• Not all types of pesticides are surveyed in every crop in every year 

• Many specialty crops with very small acreages are not included in the survey 

The result of these limitations is that CRDs that show no usage may actually have a small 

amount of the active ingredient being used. 

The denominator (1,000 Acres ofland in farms) was selected from the Census of Agriculture 

(USDA, 2007) to represent agricultural acreage that is actively managed and includes most of the 

8 
areas treated with pesticides. The category "Land in Fanns" is defined by the Census of 

Agriculture as being made up of four components: 

• Total cropland 

• Permanent pasture 

• Total woodland 

• Land in fannsteads, buildings, livestock facilities, ponds, roads, wasteland, etc. 

This category includes land in the various USDA conservation programs. It should be noted that 

the Census of Agriculture does not include grazing land rented (on a per-animal basis) from the 

Bureau of Land Management or Forest Service, thus it is an underestimate of the land being 

managed for agricultural purposes. 

The reader should pay particular attention to the figure legends and realize that a map prepared 

for a particular chemical is not directly comparable to a map prepared for a different chemical. 

Scale and units of measurement do matter and may be different between maps. 

9