UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

JJUl l 0 2014 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

BEAD Chemical Profile for Registration Review: Imazapic (129041) and 

Imazapic-ammonium ( 12894?Yir 3) 

Sunil Ratnayake, Biologist 

Biological Analysis Branch 

Cynthia Doucoure, Environmental Protection Specialist 

Science Information and Analysis Branch 

Elizabeth Hill, Economist 

Economic Analysis Branch 

Biological and Economic Analysis Division (750 

Arnet Jones, Chief 

Biological Analysis Bra h 

Science 

Diann Sims

Information 

, Chief ~ and An~alysis Branch~ 

Timothy Kiely, Chief 

Economic Analysis Branch \AA 

Biological and Economic An Division ( 0 P) 

Ricardo Jones, Chemical Review Manager 

Risk Management and Implementation Branch V 

Pesticide Re-evaluation Division (7508P) 

Product Review Panel date: June 11, 2014 

Page 1 ofll 
SUMMARY 

Imazapic (imazapic and imazapic ammonium) is a systemic herbicide used for the control of 

certain annual and perennial grasses and broadleaf weeds in non-crop lands. This includes utility 

plant sites, airports, and turf areas (industrial lands, golf courses, recreation and non-residential). 

Imazapic and imazapic-arnmonium are also registered for weed management in peanuts, lands 

under conservation reserve programs, pasture and rangeland. 

The predominant agricultural use of imazapic is on peanuts. Based on available data from 2004-

2012, over half of the peanut crop in the U.S. was treated with imazapic- 55 percent crop treated 

(PCT). Available data also shows that recently (2008-2012) over 98% of the total imazapic 

pounds a.i. applied was on peanuts, primarily in the states of Georgia, Alabama, and Florida, 

which represents nearly a slight increase in comparison to use from 2003-2007. Use of imazapic 

on pastureland rose sharply early on, peaking in 2002, but declined steadily afterwards. 

Recently, less than one percent of the site is treated with imazapic. As for use of imazapic in the 

non-agricultural market, available proprietary data show reported use by consumers, but the 

exact figures are not available. 

INTRODUCTION 

The purpose of this document is to convey usage information and a broad overview of the pest 

management roles of pesticides that are beginning to undergo registration review. The 

anticipated audience consists of the team of EPA staff currently evaluating the registration status 

of imazapic, and eventually the general public. This document builds upon the data. BEAD 

provides in the Label Use Information System (LUIS) reports and the Screening Level Usage 

Analysis (SLUA) to Registration Review teams. The document is based on information and data 

available to BEAD as of April2014. 

HISTORY OF BEAD ASSESSMENTS FOR IMAZAPIC 

Imazapic was registered in 1994. BEAD prepared a Screening Level Usage Analysis (SLUA) in 

April 2014 based on available data from 2004 to 2012 that showed that imazapic is used on over 

half of the peanut crop in the U.S. (55% PCT) and only a small percentage ofpastureland (<1% 

PCT). The average annual pounds a.i. applied on peanuts was 40,000 and on pastureland was 

1,000. 

BEAD has not conducted any reviews of requests for Section 18 Emergency Exemptions for the 

use of imazapic in the past ten years. This should not be interpreted as a lack of benefits derived 

from imazapic. 

COMMON FORMULATIONS AND APPLICATION METHODS 

Imazapic products are formulated as granules, water dispersible granules (dry flowable ), soluble 

concentrates, as well as ready-to-use solutions. 

Page 2 ofll 
USE SITES 

Agricultural Use Sites: 

Imazapic is registered for use peanuts, pastureland/rangeland, and land under conservation 

reserve programs. 

Non-Agricultural Use Sites: 

Imazapic is registered for use on non-crop areas including rights-of-way, non-residential turf, 

and wildlife habitat management. 

IMAZAPIC USAGE 

Agricultural Usage Trend 

According to proprietary market research surveys, imazapic is reported to be used predominantly 

on peanuts and pastureland during the 1998-2012 time period. Reported use ofimazapic on 

peanuts was variable throughout these years resulting in an indiscernible trend; pastureland use 

spiked in 2002 and decreased afterwards. Similar trends were found for the total area treated 

with imazapic as shown in Figure 2. During this period, the overall average annual pounds a.i. 

applied on peanuts was 38,000 lbs. used to treat an average of 680,000 acres at an overall 

application rate of0.06lb a.i. per acre. Recently, however, as shown in Table 1, the average 

annual pounds a.i. applied increased to 42,600. The maximum labeled application rate for 

peanuts is 0.063 lb a.i. per acre. On pastureland during this period, an average of3,800 pounds 

a.i. were applied annually on 47,000 acres at an overall application rate of 0.08 lb a.i. per acre. 

Recently, however, as shown in Table 1, the average annual pounds a.i. applied decreased 

significantly to 600. The maximum labeled application rate for pastureland is 0.199 lb a.i. per 

acre. 

Page 3 ofll 
Figure 1. Imazapic Usage on Peanuts and Pastureland: Pounds AI Applied, 1998-2012 

"C 

.!!:! 

0.. 

a. 

<( 

<i. 

"C "' 

c: 

:J 

0 

~ 

60000 

0 

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 

Year 

- Pastureland - Peanuts 

Source: EPA Proprietary Data, 1998-2012 

Figure 2: Imazapic Usage on Peanuts and Pastureland: Total Area Treated, 1998-2012 

"C 

<II 

-ro 

<II 

... 

1-

ro 

<II 

... 

<( 

ro 

~ 

1200000 

0 

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 

Year 

- Pastureland - Peanuts 

Source: EPA Proprietary Data, 1998-2012 

Page 4 ofll 
Agricultural Usage: Top Crops 

Imazapic is used primarily on peanuts and accounts for over 98% of the total pounds a.i. applied 

in recent years (2008-2012), which represents a slight increase in comparison to use between 

2003-2007. Imazapic use on pastureland has decreased by over 80% in recent years. The 

average a.i. rate of application increased slightly on pastureland but remained the same on 

peanuts during both periods while the number of applications for all sites remained the same as 

shown in Table 1. 

Table 1. Imazapic: Comparison of Usage on Crops between 2003-2007 and 2008-2012 

Timeframes. 

2003-2007 ,J 2008-2012 

Avg Annual Lbs A.I. Applied, Avg Annual Lbs A.l. Applied: 

Peanuts - 42,000 Peanuts- 42,600 

Pastureland- 3,600 Pastureland - 600 

Crop Avg. A.I. #of Crop Avg. A.I. 

Proportion Rate of Apps Proportion Rate of 

of Total Application of Total Application 

Lbs A.l. of (lb Lbs A.I. of (lb 

Applied a. i./acre) Applied a.i./acre) 

Peanuts 92% 0.06 1.0 Peanuts 98.6% 0.06 

Pasture land 8% 0.09 1.0 Pastureland 1.4% 0.14 

Source: Propnetary Data, 2003-2012 

Agricultural Usage: Top States 

#of 

Apps 

1.0 

1.0 

Imazapic is used primarily in Georgia on peanuts during the 2003-2012 time period where in 

recent years over 50% of total pounds a.i. were applied. Alabama and Florida follow, each with 

15% of the total pounds a.i. applied. In the earlier period, the proportion of total pounds a.i. 

applied in Texas was significant at 11% but decreased in more recent years to less than 5%. This 

is attributed to no reported use on pastureland and decreased use on peanuts. Usage of imazapic 

in South Carolina picked up slightly in more recent years, accounting for 7% of the pounds a.i. 

applied. 

Page 5 ofll 
Table 1. Imazapic: Comparison of Usage in States between 2003-2007 and 2008-2012 

Timeframes. 

2oo3-2oo1 1 2008-2012 

A vg Annual Lbs A .I. Appliedt A vg Annual Lbs A. I. Applied: 

Peanuts- 42,000 Peanuts - 42,600 

Pastur:eland- 3,600 Pastureland - 600 

State Avg. A.I. #of Crop Avg. A.I. 

Proportion Rate of Apps Proportion Rate of 

of Total Application of Total Application 

Lbs A.I. of (lb Lbs A.I. of (lb 

Applied a. i./acre) Applied a.i./acre) 

Georgia 49% 0.05 1.0 Georgia 53% 0.06 

Alabama 13% 0.05 1.0 Alabama 15% 0.05 

Florida 12% 0.05 1.0 Florida 15% 0.06 

Texas 11% 0.07 1.0 South 7% 0.06 

Carolina 

Other* 15% 0.02-0.17 1.0 Other 10% 0.04-0.19 

#of 

Apps 

1.0 

1.0 

1.0 

1.0 

1.0 

Other states include AR, ID, KS, MT, NE, Other states include ID, KS, MS, MT, NE, 

NM, NC, ND, OK, SC, SD, UT, VA, and WY NC, ND, OK, SD, TX, VA, and WY 

Source: Propnetary Data, 2003-2012 

Agricultural Use Intensity oflmazapic Use in the U.S. 

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 active ingredient applied per 1,000 acres of crop 

acres grown. This differs from the application rate, which is expressed as the pounds a.i. applied 

per treated area. Figure 3 spatially represents imazapic's use intensity in the U.S. in the Southeast 

states of Georgia, Florida, Alabama, and South Carolina on peanuts. For more information about 

this map, see Appendix A. 

Page 6 ofll 
Figure 3. Annual Average Agricultural Use Intensity of Imazapic (2008-2012). 

Pounds Active Ingredient 

per 1. 000 Crop Acres Grown 

CJ No Oata 

CJ <ODG 

. 0.06 · 0.27 

. 0.28 ·1 .65 

- >1 .65 

(Source: Proprietary Data, 2008-2012) 

Non-Agricultural Usage 

BEAD reviewed available data and found that there is reported use of imazapic by consumers 

but the data are not quantified and exact figures were not available (Proprietary Data, 2010, 

2012). 

Page 7 ofll 
BIOLOGICAL ASPECTS RELEVANT TO IMAZAPIC 

Imazapic belongs to the imidazolinone family of herbicides. It is a systemic herbicide registered 

for the control of certain annual and perennial grasses and broadleaf weeds. Imazapic can be 

applied as pre-and post-emergence treatments and is active at low rates. For example, for 

roadside vegetation management the typical application rate used was 0.09 lbs a.i. per acre per 

year (Washington State Dept. of Transportation (Undated). The maximum labeled application 

rate for non-crop areas including roadsides is 0.19 lbs a.i. per acre (Washington State Dept. of 

Transportation (Undated). 

According to the Weed Science Society of America (WSSA) classification of mechanism of 

action of herbicides, imazapic is classified as a Group 2 herbicide (ALS inhibitors) (WSSA, 

2013). The mechanism of action of Group 2 herbicides is inhibition of the enzyme acetolactate 

synthase (ALS), which is also called the acetohydroxy acid synthase (AHAS). It is an enzyme 

involved with the biosynthesis of branched chain amino acids such as leucine, isoleucine, and 

valine (WSSA, Undated). 

Imazapic is absorbed by roots and foliage of weed species and rapidly translocated to the 

growing points. Growth of susceptible weeds is inhibited within a few hours after the 

application of imazapic and injury symptoms appear 1 to 2 weeks after the application. Major 

injury symptoms include chlorotic meristematic areas followed by general foliar chlorosis and 

necrosis (Herbicide Handbook, 2007). The availability of soil moisture is important for the 

activity of imazapic. When adequate soil moisture is available, imazapic provides residual 

activity on susceptible germinating weeds (Herbicide Handbook, 2007). 

Depending on the application rates, rotational restrictions are applied on certain crops up to 48 

months after the application of imazapic. For example, if imazapic is applied at a rate of 9 to 12 

ounces of product per acre for weed control in Conservation Reserve Program (CRP) lands, for 

crops such as canola, potatoes, or sugar beets a minimum plant back interval of 48 months is 

recommended (Imazapic 2SL, Product Label, Undated). The long rotational intervals of imazapic 

may interfere with some crop rotations. 

ROLE OF IMAZAPIC IN PEST MANAGEMENT 

Imazapic is applied for the control of annual and perennial grasses and broadleaf weeds in noncrop lands, pasture and range lands, and conservation reserve programs. 

Imazapic is registered for the control of certain annual and perennial grasses and broadleaf weeds 

in non-agricultural lands which include: lands in CRP, pasture and range lands, utility plant sites, 

airports, and turf areas (industrial lands, golf courses, recreation and non-residential). Also, 

imazapic is registered for weed management in peanuts. In pasture and rangelands, annual weeds 

are effectively controlled with pre-emergence applications of imazapic up to small, actively 

growing plants (Prather, 2013 ). 

Page 8 ofll 
From 2003 to 2012, over 90% ofimazapic (lbs a.i.) was applied on peanuts (Table 1). When 

applied as early post-emergence treatments for weed control in peanuts, imazapic provides 

excellent control of many broadleaf and grass weeds, including both purple and yellow nutsedge 

(Marshall, 20 12). This observation, plus the relatively high usage in peanuts, suggests that 

imazapic is important in peanut weed control. 

Imazapic is used for vegetation management of roadsides. It is used to control selected annual 

and perennial grasses and broad leaf weeds and is applied for roadside vegetation management as 

a pre-emergent treatment to control undesirable grass species (Washington State Roadside 

Vegetation Management Plan, 2012). 

Of the total of 144 weed species identified with resistance to different modes of action of 

herbicides in the United States, 46 were found to have developed resistance to ALS inhibitors 

(Heap, Undated (1)). This is primarily due to the extensive use of many ALS inhibiting 

herbicides in crop production fields the United States. However, the only weed that has 

developed resistance to imazapic is Palmer amaranth (Amaranthus palmeri) (Heap, Undated (2)); 

therefore, the weed resistance does not seem to be a serious problem for imazapic users. 

INFORMATION THAT MAY BE USEFUL FOR BEAD'S FUTURE WORK ON 

IMAZAPIC 

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

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

to the use and importance of imazapic: 

• Pounds a.i. applied by consumers, on non-residential turf, and in non-crop areas 

• Typical rates of application rates on non-residential turf and non-crop areas 

REFERENCES 

Cadre® Product LabeL 2012. BASF Corporation. Online Publication. Available at: 

http://agproducts.basf.us/products/label-and-msds/cadre-herbicide-label.pdf. Accessed on May 

19, 2014. 

EPA, lmazapic Screening Level Usage Analysis (SLUA), April 2014 

EPA Proprietary Data, 1998-2012 

Heap, I. Undated (l).The International Survey ofHerbicide Resistant Weeds. Online 

Publication. 2014. Available www.weedscience.org. Accessed on Feb 12, 2014. 

Heap, I. Undated (2). The International Survey of Herbicide Resistant Weeds. Weeds Resistant 

to the Herbicide Imazapic. Online Publication. Available at: 

http://www.weedscience.org/summary/ResistbyActive.aspx. Accessed on April 7, 2014. 

Page 9 ofll 
Herbicide Handbook. 2007. Weed Science Society of America. 91

h Edition. Imazapic. pp. 82-

84. 

Imazapic 2SL Product Label. Undated. Nufarm Inc. Burr Ridge, Il 60527. Online Publication. 

Available at: http://www.cdms.net/LabelsMsds/LMDefault.aspx?pd=11734&t=1,2,3,4. 

Accessed on April 9, 2014. 

Marshall, M. 2012. South Carolina Pest Management Handbook for Field Crops- 2012. Online 

Publication. Available at: 

https :/ /www .clemson.edu/ extension/rowcrops/pest/files/20 12%20 PMH%20Web%20Page 

%20Version/2012%20PMH PEANUTWC.pdf. Accessed on June 6, 2014. 

Prather, T. 2013. Weed Control in Pasture and Rangelands. Pacific Northwest Weed 

Management Handbook. A Pacific Northwest Extension Publication. Available at: s 

http://pnwhandbooks.org/weed/other-areas/pasture-and-rangeland/weed-control-pastureand-rangeland. Accessed on April 7, 2014. 

Shinn, S. L., and D. C. Thill. 2002. The response of Yellow Starthistle (Centaurea solstitialis), 

Annual Grasses and Smooth Brome (Bromus inerrnis) to Imazapic and Picloram. Weed 

Technology. Vol. 16 (2) pp. 366-370. 

Sudianto, E., Beng-Kah, S., Ting-Xiang, N, . Saldain, N, E., Robert C. Scott, R, C., and N. R. 

Burgos 2013. Clearfield® rice: Its development, success, and key challenges on a global 

perspective. Crop Protection 49:40-51. Online Publication. Available at: 

http://www.researchgate.net/publication/257085079 Clearfield rice Its development su 

ccess and key challenges on a global perspective. Accessed on April 8, 2014. 

Summary of Herbicide Mechanism of Action. Undated. Weed Science Society of America. 

Available at: http://wssa.net/wp-content/uploads/WSSA-Mechanism-of-Action.pdf. 

Accessed on March 31, 2014. 

Imazapic Washington State Department ofTransportation. Undated. Roadside Vegetation 

Management Herbicide Fact Sheet. Online publication. Available at: 

http://www.wsdot.wa.gov/nr/rdonlyres/67f89cb7-d919-47dd-890febabbbd32e6e/O/imazapic.pdf. Accessed on May 19, 2014. 

Integrated Roadside Vegetation Management Plan. 2012. Washington State Department of 

Transportation. Online Publication. Available at: 

http://www. wsdot. wa.gov/NR/rdonlyres/C7DDC83D-C8DA -416C-AC09-

36EBAB243329/0/Herbicide List.pdf. Accessed on May 16, 2014. 

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

Action. Online Publication. Available at: http://wssa.net/wp-content/uploads/WSSAMechanism-of-Action.pdf . Accessed on March 20, 2014. 

Page 10 of 11 
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 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 ai/ 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 

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. 

Page 11 ofll