UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

ocr o 1 2014 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

BEAD Chemical Profile (BCP) for Registration Review: Clopyralid 

Case (117401, 117403, 117404, and 117423) 

Sunil Ratnayake, Biologist /"\. . \--; St__ 

Biological Analysis Branch L V\\l...cJ \ 

Sepehr 

Science 

Haddad, 

Information 

Environmental 

and Analysis 

Protection 

Branch 

Specialist Jfls ~ 

Stephen Smearman, Economist }..J._ -l,Jt-11~ 

Biological 

Economic Analy~is 

and Economic 

Branch 

Analysis 

~ 

Division (7503P) 

Timothy 

Economic Kiely, Analysis 

Chief 

Branch ~ 1!\fl ~ 

Biological and Economic Analy s Divisi n 503P) 

TO: Steve Snyderman, Chemical Review Manager 

Pesticide Re-evaluation Division (7508P) 

Peer Review Panel date: October 23, 2013 
SUMMARY 

Clopyralid was first registered as a pesticide in the U.S. in 1987 (US EPA, 1995). Clopyralid is a 

systemic herbicide that belongs to the pyridine carboxylic acid family. It is applied as a postemergence herbicide to control broadleaf weed species in many agricultural and non-agricultural 

use sites. It is no longer registered for residential use. Clopyralid acts like a plant- growth 

regulator (PGR) by mimicking natural plant growth hormones (auxins). According to the Weed 

Science Society of America (WSSA) mechanism of action ofherbicides, clopyralid belongs to 

the Group 4 herbicides (synthetic auxins). The herbicides in this group cause uncontrolled cell 

devision leading to the death of susceptible plants. Clopyralid has a long period of residual 

activity and the rotational interval for some crops is extended up to 18 months. 

Based on private market usage data from 1998-2012, usage averaged· approximately 880,000 

pounds acid equivalent (a.e.) applied annually on approximately 10.5 million acres treated. The 

average a.e. rate over this time period was 0.084 pounds a.e./acre. Available non-agricultural 

usage data for clopyralid is limited and dated. The only reported data available are for the years 

2002, 2004 and 2006 for landscaping, lawn care operators, golf courses, institutional turf, 

nursery/greenhouses, and turffarms. 

INTRODUCTION 

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

overview of the pest management roles and quantitative usage information for clopyralid. The 

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

usage data for clopyralid to describe the role of this chemical in pest management. Additional 

information on use is available in the clopyralid PRD Label Data Report in the Public Docket. 

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

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

of this pesticide. 

USE SITES 

Agricultural Use Sites 

Clopyralid registered agricultural use sites include: apples, asparagus, barley, canola, cherries, 

cole crops, Conservation Reserve Program (CRP), com (field, pop, and sweet), cranberries, mint, 

oats, pasture, rangeland, peaches, spinach, strawberries, sugar beets, and wheat. 

Non-agricultural Use Sites 

Clopyralid registered non-agricultural use sites include: cemeteries, farm buildings, fencerows, 

industrial sites, ornamental lawns and turf, ornamentals trees, athletic fields, golf fairways, parks, 

and rights-of-way. · 

Page2 
FORMULATIONS AND APPLICATION METHODS 

Clopyralid formulations include emulsifiable concentrate, soluble concentrate, solution-ready to 

use, wettable powder and water dispersible granules. Application methods include aerial and 

ground. 

HISTORY OF CLOPYRALID AND BEAD PRODUCTS 

Clopyralid is a systemic herbicide registered for use in the U.S. since 1987. A Screening Level 

Usage Analysis (SLUA) (BEAD, 2013) provides percent crop treated for crops for which usage 

data was available. The agricultural sites with the greatest number of pounds used were for 

wheat and com. In terms of the percent crop treated, sugar beets averaged 45 percent crop 

treated followed by barley with 15 percent crop treated, and cabbage with 10 percent crop 

treated. It should be noted that the SLUA timeframe covers the years 2004-2012; however, 

during the most recent timeframe of2008-2012, the use on sugar beets has now dropped to only 

10 percent of crop treated. Percent crop treated for apples, asparagus and peaches were all less 

than 1 percent. 

A search of the BEAD database for previous BEAD products for clopyralid indicates that there 

are no records of prior BEAD benefits assessments or Section 18s requests for clopyralid. 

However, a lack of Section 18 requests assessments does not specifically indicate the relative 

importance of the chemical in registered use sites. 

USAGE 

Agricultural Usage 

Based on private market usage data from 1998-2012, usage averaged approximately 880,000 

pounds active ingredient (a.e.) applied annually on approximately 10.5 million acres treated. 

The average a.e. rate over this time period was 0.084 pounds a.e./acre. Figure 1 presents 

clopyralid usage in pounds a.e. over the 1998-2012 timeframe. Figure 2 presents total area 

treated in acres over the same timeframe (Proprietary Data, 1998-2012). 

Page 3 
FIGURE 1. Clo 

"D 

.~ 

a. 

Q. 

<( 

<( 

Ill 

"D 

c 

:s 

0 

D.. 

199819992000200120022003200420052006200720082009201020112012 

Years 

Source: Proprietary Data, 1998-2012 

FIGURE 2. Clo ralid Total Area Treated in Acres 1998-2012 

Ill 

Gl 

... 

u 

<( 

.5 

"D 

Ill 

1ii 

Ill 

.. 

1-

"' Ill 

.. 

<( 

iii 

~ 

199819992000200120022003200420052006200720082009201020112012 

Years 

Source: Proprietary Data, 1998-2012 

Page4 
Table 1. Comparison of Crops with Highest Use of Clopyralid - Percent of Total Lbs. 

Applied 2003-2007 and 2008-20121 

2003-2007 2008-2012 

Average annual= 763,000 lbs/yr Average annual= 900,000 lbs/yr 

Crop %Lbs Crop %Lbs 

Com 58% Com 48% 

Wheat, Spring 17% Wheat, Spring 35% 

Sugar Beets 14% Barley 6% 

Pasture/Rangeland 7% Wheat, Winter 5% 

Barley 3% Pasture/Rangeland 3% 

Other* 1% Other* 3% 

*Other crops in the 2003-2007 timeframe include canola, winter wheat, and cabbage. Other crops in the 2008-

2012 timeframe include sugar beets, cabbage, and sweet com. 

Source: Proprietary Data, 2003 -2012. 

Table 2. Comparison of States with Highest Use of Clopyralid- Percent of Total Lbs. 

Applied (2003-2007 and 2008-2012) 

2003-2007 2008-2012 

Average annual= 763,000 lbs/yr Average annual=900,000 lbs/yr 

State %Lbs State %Lbs 

North Dakota !"9% North Dakota 34% 

Minnesota 17% Minnesota 12% 

Iowa 13% Iowa 11% 

Wisconsin 10% Nebraska 6% 

Illinois 7% Indiana 6% 

Nebraska 6% Illinois 5% 

Other* 28% Other* 26% 

*Other States in the 2003-2007 timeframe include Michigan, Texas, Indiana, Idaho, South Dakota and Ohio. 

Other States in the 2008-2012 timeframe include Wisconsin, South Dakota, Idaho, Michigan, Montana and 

Texas. 

Source: Proprietary Data, 2003 -2012 

As shown in Table 1, in terms of clopyralid' s use distribution of the total pounds applied to all 

registered agricultural crops, the major agricultural use of clopyralid for the 2003-2007 and 

2008-2012 time frames is on com (58% of total pounds applied in 2003-2007 and while still the 

leading use site, declining to 48% of the total pounds applied in 2008-2012). This is followed 

by spring wheat which increased from 17% to 35% over the same time period. Sugar beets 

accounted for 14% of the total pounds for the time period 2003-2007 has declined significantly 

dropping to less than 3% of the total pounds applied. Barley accounted for 6% ofthe total 

pounds for the 2008-2012 timeframe, an increase of 3% compared to the 2003-2007 timeframe. 

The decrease in use on sugar beets is especially significant as use dropped from approximately 

14 percent of the total pounds during the 2003-2007 timeframe compared to approximately less 

than 3 percent of total pounds during the 2008-2012 timeframe. 

North Dakota, Minnesota and Iowa were the top three states with the highest use of clopyralid in 

both time frames as shown in Table 2, with North Dakota (19%) having the highest percent of 

Page 5 
total pounds applied in both the 2003-2007 timeframe, and (34%) in the 2008-2012 timeframe. 

Usage has increased in North Dakota, while decreasing in Iowa, Minnesota and Wisconsin in the 

most recent time frame of2008-2012. 

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

pastureland at 0.196lbs a.e./acre and the lowest for spring wheat at 0.074lbs a.e./acre as shown 

in Table 3. 

Application Rates 

Table 3. Clopyralid Use on Top Crops: Average A.E. Rate, 2008-2012 

Crop 

Com 

Wheat, Spring 

Barle)'_ 

Wheat, Winter 

Pasture land 

Annual Average 

Pounds 

430,000 

317000 

58,000 

47,200 

25,600 

Annual Average 

Total Acres 

Treated* 

5,380,000 

4,300,000 

740,000 

570,000 

130,000 

A vg. A.E. Rate (lbs 

a.e./acres) 

0.080 

0.074 

0.078 

0.083 

0.196 

*Total Acres Treated sums all acres treated for a crop, mcludmg those acres that rece1ve multiple treatments. 

Source: Proprietary Data, 2008 -2012 

Geographic Distribution ofClopvralid Use 

Figure 3 provides a very broad geographical view of the average annual amount (in pounds) of 

clopyralid applied per 1,000 acres of crop acres grown. These data are included in the maps 

because risk assessors are interested in the amount of a pesticide used across agricultural land. 

The calculated values presented-in the map are not equivalent to an application rate (lb ae/A). 

As shown in the map, North Dakota and New Jersey depict high use intensity of acres treated 

with clopyralid in those states. Please see Appendix I for further information on the map. 

Page 6 
FIGURE 3. Annual Average Agricultural Use Intensity of Clopyralid (2008-2012). 

Pounds Acid Equivalent 

Per 1,000 Crop Acres Grown 

0 No Data 

0 <0.1 

o o.1-1 

1-3 

3-6 

- >6 

Non-Agricultural Usage 

Available· non-agricultural usage data for clopyralid is limited and dated. The only reported data 

for non-agricultural usage and which is available in terms of active ingredient (a.i.) are for the 

years 2002, 2004, 2006 and 2012 for landscaping, lawn care operators, golf courses, institutional 

turf, nursery/greenhouses, and turf farms as shown in Table 4. Total non-agricultural usage 

between 2006 and 2012 appears to have declined significantly. However, there is a gap in the 

data for the years between 2006 and 2012 and more recent data (data for the years between 2006 

and 2012) is not complete and are not available to determine if this is a trend as it appears to be 

or a fluctuation in use that has been recorded in a down use cycle. 

Page7 
Table 4. Clopyralid Non-A2ricultural Usa2e (Pounds A.I. (2002-2012) 

Site 2002 2004 2006 2012 

Golf Courses 8,250 35,900 11,800 15,000 

Institutional Turf 11,250 2,300 4,700 * 

Landscape 5,700 133,400 5,900 - Lawn Care Operators 64,600 18,700 11,150 * 

Nursery/Greenhouse 360 1,150 5 * 

TurfFanns 13,500 50 900 -

TOTAL 103,660 191,500 34,455 N/A 

Source: Proprietary Data 2002, 2004, 2006, and 2012 

• Proprietary data for 2012 reports usage of clopyralid as a post emergent control used in coformulated products. However, it is not possible to disaggregate the number of pounds a.i. from the 

estimate provided. A dash ( - ) indicates that there is no reported usage. It is estimated that the total 

usage is less than or equal to 20,000 pounds ai. N/ A indicates that the total number of pounds 

applied in 2012 is not known. 

BIOLOGICAL ASPECTS RELEVANT TO CLOPYRALID 

Clopyralid is a selective systemic herbicide that belongs to the pyridine carboxylic acid family. 

Aminopyralid, fluroxypyr, and triclopyr are the other herbicides that belong to the pyridine 

carboxylic acid family. 

Clopyralid can be applied as a post-emergence herbicide to control broadleafweed species in 

many agricultural and non-agricultural use sites and there are no residential uses of this 

herbicide. According to the Weed Science Society of America (WSSA) mechanism of action 

classification, clopyralid belongs to the group of synthetic auxins (Group 4) (WSSA, 2013). 

These herbicides act like natural plant growth regulators by mimicking plant growth hormones. 

Clopyralid is absorbed by the plants through foliage and roots (Che~icalWatch Fact Sheet, 

2013). Application of herbicides belonging to group 4 causes uncontrolled cell devision leading 

to the death of susceptible plants. 

According to the available information, more than 50 broadleaf weeds can be controlled by 

application of clopyralid (Stinger product label, 2010). To achieve a broader spectrum of weed 

control, clopyralid can be tank mixed with other synthetic plant growth regulators such as 

MCPA, 2,4-D, and triclopyr. Application rate of clopyralid varies depending on the type of crop 

(barley, canola, leafy vegetables, and field com etc.), type of weeds (annual, perennial), growth 

stage of the weed species, and the type of land (cropping or fallow land. According to the 

International Survey of Herbicide Resistant Weeds, biotypes of 8 weed species have developed 

resistance to the mode of action of Group 4 herbicides in the United States. However, no reports 

could be found on the development of weed resistance, specifically to clopyralid in the United 

States (International Survey ofHerbicide.Resistant Weeds, 2013). 

Clopyralid can persist in soil for a long period depending on the factors such as rainfall and 

organic matter content in the soil (Stinger product label, 201 0). Due to this long period of 

residual activity, the rotational interval for some crops such as cotton, sunflower, potato, lentils, 

and peas is extended up to 18 months depending on the soil and weather conditions of different 

Page 8 
states (Stinger product label, 201 0). Grass clippings from the pasture or hay fields sprayed with 

clopyralid can contaminate the compost and the use of contaminated compost with clopyralid has 

resulted in crop injuries even a year after the initial application (Miltner et al., 2003). 

ROLE OF CLOPYRALID IN PEST MANAGEMENT 

Clopyralid is an herbicide widely used to control common broadleafweeds including invasive 

and noxious weeds on agricultural as well as non-agricultural areas (Clopyralid Fact Sheet, 

2013). Clopyralid is registered for the control of a variety of annual and perennial broadleaf 

weeds, including corn marigold (Chrysanthemum segetum) and especially the invasive weed 

creeping thistle ( Cirsium spp. ), in established grassland, non-crop land and ornamentals 

(Herbicide Handbook, 2003). Clopyralid has a niche use in that and it is used as a post harvest 

treatment in the field to control thistle, especially in sugar beets and small grains. However, 

because clopyralid can persist in the soil, some sensitive crops to clopyralid such as dry beans, 

sunflower, peas, and potatoes, have a long rotational period to avoid potential crop damage 

(Morishita, 2003). With the introduction of Roundup Ready® sugar beets in 2008, growers are 

now able to have successive plantings of other crops without the worry of crop damage that 

could occur due to the residual activity of clopyralid. The increased use of gylphosate may be a 

factor contributed to the declining use of clopyralid in sugar beets from 2008-2012. 

In addition, clopyralid can also be used for turf and golf course management and by landscape, 

nursery/greenhouse and lawn care operators. Based on the timeframe from 2002 to 2006 it 

appears that use on non-agricultural sites has significantly declined over the last 10 years 

although the data are incomplete for the reporting year 2012. 

The overall picture for clopyralid use is mixed. The total pounds of active ingredient applied 

(Figure 1.) over the time period from 2000 to 2012 appears to be increasing after a period of 

decline as the total pounds applied in 2012 near the amounts applied in 2000. Ill addition the 

overall number of acres treated has increased over the last five years indicating that clopyralid 

has found niche uses in field crops such as barley and spring and winter wheat. These are major 

field crops with large numbers of acres grown so small percentage increases in use on these 

crops translates into large increases in the percentages of total acres treated with clopyralid. 

DATA NEEDS 

The Agency currently does not have important information on clopyralid. Obtaining the 

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

use and importance of clopyralid. Information needed includes why after years of decline is 

clopyralid use increasing especially for particular crops, how is it being used, how much is used, 

what is the typical rate for each use site and how it is applied. Additional information is needed 

for the following uses: 

Page 9 
Agricultural Use 

Since BEAD proprietary databases do not contain survey data on registered agricultural 

sites such as mint, lentils, and macadamia nuts, and usage data for all sights such as the 

pounds a. e. applied, application method, percent of the crop treated and application rates 

would be beneficial. 

Non Agricultural Use 

BEAD has very limited recent (post-2006) usage data except for available data from 2012 

for golf courses. Information needed includes the pounds a.i. applied, application rates, 

application method and percent crop treated for the following: institutional turf, 

landscaping, nursery/greenhouses, and turf farms. 

APPENDIX I. 

The map included herein is 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 average annual 

amount (in pounds) of the active ingredient applied per 1 ,000 acres of crop acres grown. These 

data are included in the maps because risk assessors are interested in the amount of a pesticide 

used across agricultural land. The calculated values presented in the map are not equivalent to 

an application rate (lb ae/ A). 

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

should consider the underlying data and the associated limitations carefully. 

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 surveys. 

• 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 states that show no usage may actually have a small amount 

of the active ingredient being used. In some cases the displayed use intensity may be distorted 

because the surveyed crops and the reported pesticide usage may not accurately represent the 

actual pesticide usage on the crops produced in the state. 

The denominator (1 ,000 crop acres grown) was also obtained from the same private market 

survey database. The "Crop Acres Grown" variable represents the total acres grown in a given 

state of all of the surveyed crops. This value is independent of pesticide usage and pesticide 

registration. It is important to note that the surveyed crops (about 60) are sampled from states 

that are major producers of each crop. Therefore, there are cases where the actual crop acreage in 

Page 10 
a state is higher than that reported by crop acres grown in the survey because either that state 

and/or crop was not included in the survey. 

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 as 

the legend bins will likely be different. 

REFERENCES 

BEAD, 2013. Clopyralid Screening Level Usage Analysis. Biological and Economic Analysis 

Division, Office of Pesticide Programs, US Environmental Protection Agency. March 19. 

Britt, C., A. Mole, F. Kirkham and A. Terry. 2003. Herbicide Handbook, Guidance on the use of 

herbicides on nature conservation sites. Publication of English Nature. PO Box 1995, 

Wetherby, West Yorkshire LS 23 7XX. http://www.naturalengland.org.uk/. Access on 

Oct. 25, 2013. 

Clopyralid. 2013. Chemical Watch Fact Sheet. On line Publication. 

http://www.beyondpesticides.org/pesticides/factsheets/clopyralid.pdf. Accessed on Oct. 

29,2013. 

International Survey of Herbicide Resistant Weeds. 2013. 

http://www.weedscience.org/surrunary/MOASummary.asp Accessed on Feb. 25, 2013. 

Proprietary Data, 2002, 2004, 2006 and 2012. (non-agricultural usage data) 

Miltner, E., et al. 2003. Clopyralid and Compost: Formulation and Mowing Effects on Herbicide 

Content of Grass Clippings. Compost Science & Utilization. 11(4): p. 289-299. 

Morishita, D. W. 2003. Herbicides for Weed Control in Sugar Beets. 

http://www.uiweb.uidaho.edu/sugarbeet/weed/Herbicides%20for%20sugar%20beets.pdf 

Accessed on Dec.19, 20 13. 

Nickerson, C., R. Ebel, A. Borchers, and F. Carriazo. 2011. Major Uses of Land in the United 

States, 2007. USDAIERS. Economic Information Bulletin Number 89. 

Proprietary Data. 1998-2012. (pesticide usage data) 

Stinger product label. 2010. Dow AgroSciences LLC. 9330 Zionsville Road, Indianapolis, IN 

48268. 

US Census. 2012. Statistical Abstract of the United States 2012. Table 358. 

Page 11 
USDA. 2006-2010. NASS Crop Reporting Districts (shape file ofCRDs). Available at: 

http://www.ers.usda.gov/briefing/anns/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 0 

uestions/county list.txt 

USDA. 2007. Census of Agriculture. Online: 

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

USDA, 2007. Census of Agriculture. Land in Farms data). Available at: 

http://www .agcensus. usda. gov /Publications/2 007 /index.asp. 

WSSA. 2013. Summary of Herbicide Mechanism of Action According to the Weed Science 

Society of America (WSSA). 

http://wssa.net/wp-content/uploads/WSSA-Mechanism-of-Action.pdf. Accessed on Feb. 25, 

2013. 

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