UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MAR 21 2014 OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENT ION 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

BEAD Chemical Profile (BCP) for Registration Review: Aminopyralid Case 

Level Composed of Aminopyralid (0051 00), Aminopyralid, Potassium Salt 

(005219) and Triisopropanolamine Salt of Aminopyralid (005209) 

S~nil ~atnayake, ~iologist r-l . ~ £ 

Biological Analysis Branch \._, '"'-A.... "'-~1tA../"""---

Rafael A. Prieto, Environmental Protection Special~st ,J7/ h-t-J 1: -f?vjJ{o Science Information and Analysis Branch ·. · f t- -

Stephen Smearman, Economist 

Economic 

Biological 

Analysis 

and Economic 

Branch 

Analxsis Division (7503P) 

~ 

Arnet Jones, Chief 

Biological Analysis Br 

Diann Sims, Chief 

Science Information and Analysis Branch 

Timothy Kiely, Chief /l10t~W~ I~ Economic Analysis Branch 

Biological and Economic Analysis Division (7503P) 

TO: Veronica Dutch, Chemical Review Manager 

Risk Management and Implementation Branch 5 

Pesticide Re-evaluation Division (7508P) 

Peer Review Panel date: March 19, 2013 
SUMMARY 

Aminopyralid was registered in the U.S. in 2005 and is a systemic herbicide used for the control 

of broadleaf weeds in forage and grass crops and agricultural and non-agricultural lands. 

Registered agricultural use sites for this case include corn (silage/field), wheat, hay and pasture 

crops and forest plantings. It is also used on fallow and on Conservation Reserve Program (CRP) 

lands. The registered non-agricultural use sites include airports/landing fields, industrial and 

construction areas. 

Aminopyralid controls many annual, biennial, and perennial broadleaf weeds in pasture lands 

including invasive weed species (SDSU, 2013). More than 98 percent of aminopyralid's 

reported use is on pasture, with about 40 percent of this use reported for Texas .. Aminopyralid is 

an important component of integrated vegetation management programs to renovate or restore 

desired plant communities. It has long residual activity which can reduce weed re-infestation and 

the need for re-treatment. Depending on the environmental conditions, an interval of at least two 

years is required before re-planting of a broadleaf crop. 

Aminopyralid belongs to the pyridine carboxylic acid family. It can be applied as pre-emergence 

or post-emergence treatments using aerial and ground application methods. According to the 

Weed Science Society of America (WSSA) classification of herbicides, aminopyralid belongs to 

Group 4 (synthetic auxins). Group 4 herbicides mimic natural plant growth hormones (auxins) 

and cause uncontrolled cell devision which leads to the death of susceptible plants. 

INTRODUCTION 

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

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

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

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

Additional information on use is available in the aminopyralid PRD Label Data Report. 

Information provided in this BEAD Chemical Profile (BCP) may be used by stakeholders (e.g., 

users and registrants), OPP risk assessors, and OPP risk managers, and the general public during 

the Registration Review process of this pesticide. 

Aminopyralid was registered in the U.S. in 2005 (EPA, 2013). This pesticide belongs to the 

pyridine carboxylic acid family and used as a pre-emergence as well as a post-emergence 

herbicide to control broadleafweed species in many agricultural and non-agricultural use sites 

described below. It is a systemic herbicide which provides a broad-spectrum control of number 

of noxious and invasive annual, biennial and perennial weed species. Depending on application 

rate and target weeds, arninopyralid provides residual control which helps avoid weed reinfestations and minimizes the need for re-treatment. 

Page 2 
USE SITES 

Registered agricultural use sites for aminopyralid include wheat, hay and pasture crops. 

Registered use sites for aminopyralid potassium salt are forestry plantings, wheat, hay, and 

pasture crops. It is also used on Conservation Reserve Program (CRP) lands, rights-of-way, 

fallow and non-agricultural uncultivated areas including seasonally flooded wetland areas when 

dry. 

Registered use sites for aminopyralid triisopropanolamine salt include forestry plantings, wheat, 

corn (field/silage), hay and pasture crops. Its other uses include CRP areas, airports/landing 

fields, industrial and construction areas, fallow and non-agricultural uncultivated areas, including 

seasonally flooded wetland areas when dry. 

FORMULATIONS AND APPLICATION METHODS 

Aminopyralid is formulated as an emulsifiable concentrate. Aminopyralid potassium salt is 

formulated as a dry flowable and emulsifiable concentrate. Aminopyralid triisopropanolamine 

salt is formulated as ·emulsifiable concentrate, liquid soluble concentrate, and flowable 

concentrate. Aminopyralid can be applied pre-emergence or post-emergence using aerial and 

ground application methods. 

HISTORY OF AMINOPYRALID and BEAD PRODUCTS 

Aminopyralid is a selective systemic herbicide registered for use in the U.S. in 2005 for control 

of certain woody plants and broadleaf weeds such as thistles. A Screening Level Usage Analysis 

(SLUA) was prepared by BEAD for this chemical in 2014 that provides percent crop treated for 

fallow, winter and spring wheat and pastureland for which usage data was available. The highest 

number of pounds of acid equivalent used over the SLUA timeframe (2004-2012) was on 

pasture land which accounted for over 98 percent of the aminopyralid usage, which accounts for 

approximately 2.5 percent crop treated for pastureland. This was followed by winter wheat and 

spring wheat with approximately one half of one percent each of the usage. The relatively low 

percent crop treated for pastureland may not be an indication of a lack of overall benefit to 

growers as pasture is a very low input site. 

There are no records of prior BEAD assessments relevant to the benefits of aminopyralid. 

USAGE 

Usage Trends 

Use in terms of both pounds a. e. and total area treated increased steadily following this 

chemical's registration in 2005, leveling out after 2009 (Proprietary data, 2006-2012). Since 

2009, aminopyralid annual agricultural usage averaged 142,000 pounds a.e. treating an average 

of 2.1 million acres, for an overall average application rate of 0.07 pounds a.e. per acre. 

Page 3 
Figure 1 presents aminopyralid's usage in pounds a.e. over the 2006-2012 timeframe. Figure 2 

presents total area treated in acres over the same timeframe. 

Fi ure 1. Amino ralid Total Pounds A.E. 2006-2012 

180,000 

2006 2007 2008 2009 2010 2011 2012 

Year 

Source: Proprietary Data, 2006-2012. 

Fi ure 2. Amino ralid Total Area Treated in Acres 

2,500,000 

2006 2007 2008 2009 2010 2011 2012 

Year 

Source: Proprietary Data, 2006-2012. 

As shown in Table 1> pastureland is the highest use site for aminopyralid, both in terms of 

pounds a. e. and in total area treated. More than 98 percent of aminopyralid's use is on 

pastureland, with about 40 percent of the use aminopyralid in Texas as shown in Table 2. The 

highest average application rate is on pastureland with 0.07lb a.e./acre as shown in Table 3. 

Page4 
Table 1. Crops with Highest Use of Aminopyralid- Percentage of Total Lbs. A.E. Applied 

on Pastureland. 

2006-2012 

Crop %LB 

Pastureland 98.7 

Source: Proprietary Data, 2006-2012 

Table 2. States with Highest Use of Aminopyralid-% of Total Lbs. Applied (2006-2012) 

2006-2012 

State %Lbs 

Texas 42 

Oklahoma 6 

Georgia 5.2 

Minnesota 5.1 

Virginia 5 

Source: Proprietary Data, 2006-2012. 

Application Rates 

T a e bl 3 A . mmopyra . rd 1 u se on c rops: A vera~e AE . . R ate, 2006 -2012 on p asture I an d 

Crop Average Pounds Average Total Acres Avg. AI Rate 

Treated* (lbs a.e.lacres) 

Pasture land 92,000 1,307,000 0.069 

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

Source: EPA Proprietary Data, 2006-2012 

Page 5 
Geographic Distribution of Aminopyralid Use 

Another measure of usage is the use intensity. In this analysis, the use intensity is expressed as 

the average annual amount (in pounds) of the acid equivalent applied per 1,000 acres of crop 

acres grown, including pasture. This differs from the application rate, which is expressed as the 

pounds a.e. applied per treated area. Figure 3 spatially represents propargite use intensity in the 

U.S. Use is widespread, but at very low level; in most states, use is less than one pound a.e. per 

1,000 acres in crops. Use is relatively more intense in areas ofthe southeast, from Texas through 

Georgia and South Carolina. Compared to western states, where livestock are grazed 

extensively, pastures in the southeast are more intensively managed. 

Pounds Acid Equivalent 

Per 1,000 Crop Acres Grown 

D No Data 

c:J <0.1 

. 0.1· 0.5 

. 0.5 · 1 

- >1 

Figure 3. Annual Average Agricultural Use Intensity of Aminopyralid (2008-2012). 

(Source: Proprietary Data) 

For more information about the methodology used to create this map, see Appendix A. 

Non-Agricultural Usage 

No usage data is available for non-agricultural uses of these chemicals. There is some 

indication that there is use for industrial and institutional vegetation management, but BEAD 

does not have any usage data available for these sites. 

Page 6 
BIOLOGICAL ASPECTS RELEVANT TO AMINOPYRALID 

Aminopyralid is a selective systemic herbicide used for the control of broadleaf weeds in many 

agricultural and non-agricultural sites. It can provide broad-spectrum control of number of 

noxious and invasive annual, biennial and perennial weed species. Aminopyralid can be applied 

as post-emergence treatments to control the emerged weeds and pre-emergence treatments to 

control germinating seeds or emerging seedlings of susceptible broadleaf weeds. Aminopyralid 

is absorbed by the plants through foliage and roots and translocated throughout the plant 

(Herbicide Handbook, 2007). According to the Weed Science Society of America (WSSA) 

mechanism of action of herbicides, aminopyralid belongs to the Group 4 herbicides (synthetic 

auxins). Herbicides in this group acts like a plant growth regulator by mimicking natural plant 

growth hormones (auxins) and cause uncontrolled cell devision leading to the death of 

susceptible plants (WSSA, Undated). Herbicide injuries to non-target broadleafplants have been 

reported due to the use of compost, manure, or urine from animals consuming grass or hay 

treated with this pesticide. 

ROLE OF AMINOPYRALID IN PEST MANAGEMENT 

Aminopyralid is a herbicide used to manage broadleaf weeds including invasive and noxious 

weeds on rangeland, grass pastures, conservation reserve lands, and non-crop land areas such as 

roadsides, non - irrigation ditch banks, recreation areas, and campgrounds (USEPA, 2005; 

SDSU, 2010, SDSU, 2013). Aminopyralid is an important component of integrated vegetation 

management programs to renovate or restore desired plant communities. More than 98 percent of 

aminopyralid use is for weed control in pasturelands (Table 1). Aminopyralid controls many 

annual, biennial, and perennial broadleaf weeds in pasturelands including invasive weed species 

(SDSU, 2013). Canada thistle (Cirsium arvense), perennial showthistle (Sonchus arvensis), 

tansy ragwort (Senecio jacobaea), absinth wormwood (Artemisia absinthium), Russian 

knapweed (Acroptilon repens), spotted knapweed (Centaurea stoebe) are some of the weed 

species that can be controlled by applications of aminopyralid in pasturelands (SDSU, 2013). In 

wheat, aminopyralid can be applied for control of key broadleaf weeds, including wild 

buckwheat (Polygonum convolvulus), prostrate knotweed (Polygonum aviculare), milk thistle 

(Silybum marianum), and com marigold (Chrysanthemum segetum) (Herbicide Hand Book, 

2007). 

Aminopyralid can provide long residual weed control of some of these weeds such as knap 

weeds (Centaurea diffusa) and thistle species (Cirsium arvense; Carduus nutans) (BASF, 2012; 

Endres & Kline, 2011). Use ofaminopyralid can avoid weed re-infestations and minimize the 

need for re-applications. This is a particular benefit for use in pasture, but can complicate crop 

rotations between grain crops and crops such as beans and oilseeds. 

The spectrum of weeds controlled by aminopyralid can be maximized by tank mixing 

aminopyralid with other herbicides such as 2, 4-D, and triclopyr (SDSU, 201 0; Dow Agro 

Sciences, Undated). According to the International Survey of Herbicide Resistant Weeds, 

biotypes of eight weed species have developed resistance to the Group 4 herbicides. However, 

weed resistance specifically to aminopyralid has not been reported (Heap, Undated). 

Page 7 
DATA NEEDS 

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

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

use and importance of aminopyralid. 

Data on aquatic uses (usage on sites that may be seasonally flooded or tidal. Wetlands, 

marshes, swamps, bogs, river and stream channels etc.). 

Agricultural Use 

BEAD proprietary databases contains some survey data on registered agricultural sites 

such as wheat, hay, and pasture but quantifiable usage data such as pounds a.e. applied 

and application rate information would be useful if available. BEAD does not have 

detailed agricultural usage information on sites such as rangeland. Usage data such as 

pounds a.e. applied and application rates would be useful for all sites that have 

tolerances. 

Non Agricultural Use 

BEAD does not have detailed non-agricultural usage on the following sites: rangeland, 

conservation reserve lands, and non-crop land areas such as roadsides, non - irrigation 

ditch banks, recreation areas, and campgrounds. Usage data such as pounds a.e. applied 

and application rates would be useful if available. BEAD needs actual usage data so that 

we can improve our assessments. 

REFERENCES 

BASF. 2012. Invasive Plant Management with Milestone® and Other Herbicides. Guide for 

Natural Area Managers. 20 I2. Online Publication. Available at: 

http://rnsdssearch.dow.com/PublishedLiteratureDAS/dh 0898/0901 b803808981 dd.pdf?fi 

lepath=ivm/pdfs/noreg/0 I 0-50904.pdf&fromPage=GetDoc. Accessed on March II, 

20I4. 

Dow Agro Sciences. Undated. Range and Pasture. Online Publication. Available at: 

http://www.dowagro.com/range/resource/milestone faq.htrn#faq4 . Accessed on 

March18, 2014. 

Endres, G, and E. Kline. 20II. Perennial Weed Control with Aminopyralid and 

Aminocyclopyrachlor, Sheridan County. Publication of North Dakota State University. 

Online Publication. Available at: 

http://www .ag.ndsu.edu/carringtonREC/documents/agronornyrd/docs20 1112011 %20Pere 

nnial%20Weed%20Control%20with%20Arninopyralid%20and%20Aminocyclopyrachlor 

-%20Sheridan%20County.pdf/view . Accessed on March 11,2014. 

Heap, I. (Undated). The International Survey of Herbicide Resistant Weeds. Online Publication. 

Available at: www.weedscience.org. Accessed on Feb 12, 2014. 

Page 8 
Herbicide Handbook. 2007. 91

h edition. Weed Science Society of America. Aminopyralid. Pp 

331-332. 810 E. 10ih Street, Lawrence, KS 66044-8897. 

Proprietary Data. 2006-2011. (pesticide usage data). 

South Dakota State University (SDSU). 2010. Pasture and Range. Online Publication. 

Available at: http://www .sdstate.edu/ps/extension/weed-mgmt/upload/FS525P .pdf. 

Accessed on March 18, 2014. 

South Dakota State University (SDSU). 2013. Pasture and Range. Online Publication. 

Available at: 

https:/ /www. google.com/ search ?g=20 13+weed+control+SDS U+extension+south+dakota 

&rls=com.microsoft%3Aen-us%3AIE-SearchBox&oe=UTF8&rlz= 1 17RNTN enUS323&safe=on&hl=en&sa= X&as q=&nfpr=&spell= 1 &ei=H Qq 

U5HFL4-wOAG7gYHwAQ&ved=OCBg0vwU Accessed on March 18,2014. 

United States Environmental Protection Agency (USEPA). 2005. Pesticide Fact Sheet. 

Aminopyralid. 

http://www .epa.gov/oppOOOO 1 /chem search/reg actions/registration/fs PC-0051 00 1 OAug-05.pdf. Accessed on Aug. 28, 2013. 

USEPA, 2013. OPPIN database. 

Weed Science Society of America (WSSA). Undated. Summary of Herbicide Mechanism of 

Action. Online Publication. Available at: 

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

28,2013. 

Page9 
APPENDIX A 

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 amount (in 

pounds) of the acid equivalent 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 of the definition of Land in Farms, as discussed below, the calculated 

values presented in the map are not equivalent to an application rate (lbs a.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, 2007-2011). 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 acid equivalent 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 CRDs that show no usage may actually have a small 

amount of the acid equivalent 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 

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

Agriculture as being made up of four components: 

• Total cropland 

• Permanent pasture 

• Total woodland 

• Land in farmsteads, 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 ofthe land being 

managed for agricultural purposes. 

Page 10 
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. 

Page 11