UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MAY 0 1 2014 

MEMORANDUM 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: BEAD Chemical Profile for Registration Review: Imazaquin (128848) and 

Imazaquin, monoammonium salt (128840) 

FROM: 

THRU: 

Carl Chen, Biologist {__wJ( ~ Biological Analysis Branch 

Cynthia Doucoure, Environmental Protection Specialist C ~~ Science Information and Analysis Branch 

Michelle Ranville, Economist 1 /}(lf/ p;---6) 

Economic 

Biological 

Analysis 

and Economic 

Branch 

Analysis 

U 

Division 

~ 

(7503P) 

Arnet Jones, Chief /) d 1...-"'7"-.:.A 

Biological Analysis Branch ~/" 

Diann Sims, Chief 41-"~ ~.4. Science Information and Analy s Branch 

Economic 

Timothy Kiely, 

Analysis 

Chief 

Branch ~ \J....A... ~ 

Biological and Economic Analysis ivision (75 ) 

TO: Wilhelmena Livingston, Chemical Review Manager 

Risk Management and Implementation Branch V 

Pesticide Re-evaluation Division (7508P) 

Product Review Panel date: April16, 2014 

Page 1 of8 
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 imazaquin and eventually the general public. This document builds upon the data provided by 

the Biological and Economic Analysis Division (BEAD) in the Label Data 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 March 2014. 

Imazaquin, an imidazolinone herbicide, was first registered in 1986. There are currently eight 

Section 3 registrations and one 24(c) registration for imazaquin (128848) and nine Section 3 

registrations for imazaquin, monoammonium salt (128840). A Report of the Food Quality 

Protection Act (FQPA) Tolerance Reassessment Progress and Risk Management Decision 

(TRED) for Imazaquin was completed in December 2005. EPA found that the tolerance for 

imazaquin meets the FQPA safety standards. Also, per the TRED, since the ecological and 

occupational assessments were originally conducted when imazaquin was first registered, no 

further ecological or occupational assessments were conducted as part of the TRED. 

IDSTORY OF BEAD ASSESS:MENTS FOR IMAZAQUIN 

BEAD prepared a Screening Level Usage Analysis (SLUA) in 2014 which shows that an average 

of 50,000 lbs a.i. of imazaquin was applied to soybeans from 2004-2012 and that the average 

percent crop treated was less than one percent. 

BEAD has not conducted any benefits assessments for imazaquin and no Section 18s have been 

issued for this chemical. However, a lack of Section 18s does not indicate a lack of benefits for 

the chemical. 

COMMON FORMULATIONS AND APPLICATION :METHODS 

Imazaquin is commonly formulated as water dispersible granules, wettable powders, soluble 

concentrates, and emulsifiable concentrates. Imazaquin can be applied using aerial or ground 

applications. 

USE SITES 

Agricultural Use Sites: 

Imazaquin and imazaquin monoammonium salt are registered for use on soybeans and sod farms. 

Non-Agricultural Use Sites: 

Imazaquin and imazaquin monoammoniu~ salt are registered for use on landscape ornamentals, 

residential and commercial lawns and turf, 1 

~s well as golf courses. 

(1 

' ( Page 2 of8 
IMAZAQIDN USAGE 

Agricultural Usage Trend: lmazaquin Use on Soybeans 

According to proprietary market research surveys, imazaquin use on soybeans in the U.S. in 

terms of pounds a.i. applied and total area treated decreased substantially since 1998 as shown in 

Figures 1 and 2 below. During this time, an average of 132,000 lbs a.i. was applied to 1,530,000 

acres at an overall average a.i. rate of 0.09 lbs a.i. per acre. Figures 1 and 2 depict the total of 

imazaquin and its monoammonium salt. Product specific usage data shows that the same 

downward usage trend applies to both active ingredients. 

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Year 

Figure 1. Imazaquin Use on Soybeans: Pounds AI Applied, 1998-2012 

Source: Proprietary Data, 1998-2012 

Page 3 of8 

- soybeans 
- soybeans 

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Year 

Figure 2: Imazaquin Use on Soybeans: Total Area Treated Applied, 1998-2012 

Source: Proprietary Data, 1998-2012 

Agricultural Usage oflmazaguin on Soybeans in Recent Years, 2008-2012 

During the time period from 2008-2012, an average of 56,000 lbs a.i. was applied to 613,000 

acres at an overall average a.i. rate of application of 0.09 lbs a.i. per acre. The states with the 

most usage in terms of the percentage of the total pounds a.i. applied during this time were 

Indiana (37%), Ohio (33%), and Michigan (11 %) as shown in Table 1 below. The average a.i. 

rates of application and number of applications were similar across the top states. 

T a bl e 1 I mazaqum ·u se on s oy1 b eans m . M . aJor Stat es, 2008 -2012 

State Proportion of A vg A. I. Rate Avg#of Apps 

Total Lbs A.l. of Application 

Applied 

Indiana 37% 0.09 1 

Ohio 33% 0.10 1 

Michigan 11% 0.09 1 

Other* 19% 0.05-0.12 1 

*Other states include AR, IL, lA, KS, KY, LA, MS, MO, NE, NC, OK, PA, and VA 

Source: Proprietary Data, 2008-2012 

Page 4 of8 
Agricultural Use Intensity of hnazaquin on Soybeans 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 imazaquin's use intensity in the U.S. on soybeans, 

which was greatest in Ohio, Indiana, and Michigan during the 2008-2012 time frame. For more 

.information about this map, see Appendix A. 

Pounds Active Ingredient 

per 1.000 Crop Acres Grown 

CJNoData 

CJ <OD5 

. 0.05-0.17 

0.18- 0.63 

- >0.83 

Figure 3. Annual Average Agricultural Use Intensity of Imazaquin, 2008-2012 

Source: Proprietary Data, 2008-2012 

Non-Agricultural Usage 

BEAD reviewed available private market research survey data and found that there is reported 

use of 15,000 lbs a.i. of imazaquin in the turf and ornamental market, which includes 9,000 lbs 

a.i. applied by lawn care operators and 6,000 lbs a.i. applied to landscapes in the most recent year 

available (Proprietary Data). No other reports of imazaquin use were found for the nonagricultural market. 

Page 5 of8 
BIOLOGICAL ASPECTS RELEVANT TO IMAZAQUIN 

Imazaquin is an imidazolinone herbicide. The mechanism of action of this chemical family is to 

inhibit acetolactate synthase (ALS) classified by the Herbicide Resistance Action Committee 

(HRAC) and coded as HRAC Group B. It is also listed by the Weed Science Society of America 

(WSSA) as a WSSA Group 2 herbicide. Group 2 orALS herbicides are associated with the 

highest rank (3) of risk on occurrence of resistance (WSSA, 2010). Some genera composed of 

weeds targeted by imazaquin such as pigweed and barnyardgrass are also associated with the 

highest rank (3) of resistance risk (WSSA, 2010; Heap, 2010). 

ROLE OF IMAZAQUIN IN PEST MANAGEMENT 

Imazaquin is a broad-spectrum herbicide that can be applied preplant incorporated, 

preemergence, or postemergence in soybeans. It is registered to control a number of important 

weeds in soybeans including cocklebur, common lambsquarters, morning glory, redroot 

pigweed, velvetleaf, barnyard grass, and foxtail. 

The use of imazaquin in soybeans declined significantly but has remained steady since 2004. 

BEAD's SLUA showed that the average percent crop treated for soybean from 2004-2012 was 

less than 1 percent. However, the most recent available usage data shows that imazaquin use on 

soybean in the Great Lakes region (Ohio, Michigan, and Indiana) could be higher than the 

average with percent crop treated reaching up to nine percent (Proprietary Data, 2010-2012). In 

Michigan, imazaquin is recommended to control broadleaf weeds and to suppress yellow 

nutsedge in soybeans (Crop Profile for Soybean in Michigan, 2002). 

Imazaquin is registered for non-agricultural uses to control nutsedge and other annual or 

perennial weeds. In Arizona, nutsedge is a very troublesome weed in golf course and parks turf, 

and imazaquin is recommended for control of purple nutsedge in bermudagrass turf (Kopec, 

2000). Imazaquin is also currently registered under section 24(c) of the Federal Insecticide, 

Fungicide, and Rodenticide Act (FIFRA) to control red rice in soybeans in Louisiana. Although 

EPA's proprietary data does not show any recent usage ofimazaquin on soybeans in Louisiana, 

the maintenance of the registration could indicate that the chemical is important for this use. 

In general, usage of imazaquin on soybean, the only registered agricultural field crop use, has 

decreased significantly since 1998. However, the fact that usage has remained stable since 2004, 

especially in the Great Lakes region, and the recommendations for control of nutsedge in 

soybean and non-agricultural uses could indicate important niche uses for this chemical and its 

monoammonium salt. 

Page 6 of8 
INFORMATION THAT MAY BE USEFUL FOR BEAD'S FUTURE WORK ON 

IMAZAQUIN 

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

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

use and importance of imazaquin: 

• Usage information (e.g., acres treated, lbs applied, application rates, target pests) on 

ornamental lawns and turf, including golf courses and sod farms. 

• Resistance management information related to the use and importance of imazaquin in 

soybean production. 

REFERENCES 

Crop Profile for Soybean in Michigan. 2002. Online: 

http://www.ipmcenters.org/cropprofiles/docs/MISoybean.pdf. Accessed March 2014. 

EPA. 2005. Report of the Food Quality Protection Act (FQPA) Tolerance Reassessment Progress 

and Risk Management Decision (TRED) for Imazaquin. Online: 

http://www.epa.gov/oppsrrd1/REDs/imazaquin tred.pdf. 

EPA. 2005. Screening Level Usage Analysis for Imazaquin. January 28, 2005. 

EPA. 2014. Imazaquin (128848) Screening Level Usage Analysis (SLUA). March 5, 2014. 

Heap, I. 2010. International Survey of Herbicide Resistant Weeds. Online: 

http://www.weedscience.org. Accessed March 2014. 

Kopec, DM. 2000. Nutsedge Control in Turf. Online: http://turf.arizona.edu/ccps700.htm. 

Accessed March 2014. 

Proprietary Data, 1998-2012. 

WSSA, 2014. Summary of Herbicide Mechanism of Action. Weed Science Society of America. 

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

March 2014. 

Page 7 of8 
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 ail 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 8 of8