UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C. 20460 

### AUG 1 92014

OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION 

### MEMORANDUM

SUBJECT:



### FROM:

THRU:

TO: BEAD Chemical Profile (BCP) for Registration Review Imazethapyr Chemical Case [Includes Imazethapyr (128922) and Imazethapyr, Ammonium Salt (128923)] Bill Phillips, PhD, Agronomist

# ~ Biological Analysis Branch

### ~ f Rafael A. Prieto, Environmental Protection Specialist

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Science Information and Analysis Branch /

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Michelle Ranville, Economist f

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Economic Analysis Branch 

### V II**{,LAl..--6/Je.L~** Biological and Economic Analysis Division (7503P) AmetJones,Chief /)

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Diann Sims, Chief Science Information and Analysis Branch Timothy Kiely, Chief 

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Economic Analysis Branch

## V) Biological and Economic Analysis Division 503P) Katherine St. Clair, Chemical Review Manager Risk Management and Implementation Branch 2 Pesticide Re-evaluation Division (7508P)



### PeerReview Panel date: February 5, 2014

1SUMMARY Imazethapyr is an imidazolinone herbicide that inhibits the production ofthe key plant enzyme acetolactate synthase (ALS). Itis used preplantincorporated, preemergence, orpostemergence to control annual broadleafweeds and annual grasses. Based onthe percent crop treated, the two crops with the highestpercentage ofuse are greenpeas and rice. With over40% and 30%, respectively, ofthe crops receiving applications ofimazethapyritis clearthatthere is an importantuse for this herbicide inthose crops. Althoughthere are more than a dozen weed species that have biotypes which are resistant to imazethapyr, this herbicide, in combination with others, seems to be ofparticular importance for controlling some difficultto control broadleaf and grass weeds ingreen pea and rice production. In addition, imazethapyr maybe an important tool for managing weeds in an integrated weed managementprogram. INTRODUCTION The Biological and Economic Analysis Division (BEAD) Chemical Profile (BCP) provides an overview ofthe pest managementroles and quantitative usage information for imazethapyr and its amonium salt. The BCP includes summaries ofprevious BEAD products and available public and/or private use and usage data for imazethapyrto describe the role ofthis chemical inpest management. Additional information on use is available inthe imazethapyr PRD Label Data Report. Informationprovided inthis BCP may be used by stakeholders (e.g., users and registrants), OPP risk assessors, OPP risk managers, and the generalpublic during the Registration Reviewprocess for this pesticide. USE SITES Agricultural Use Sites Registered agricultural use sites for imazethapyr include: fallow/idleland /conservationreserve program (CRP), alfalfa, beans (dried-type, succulent, lima), clover, corn (unspecified, field), garbanzos (including chickpeas), lentils, lupine (grain), ornamental farms, peanuts, peas (unspecified, dried-type, southern, succulent), rice, and soybeans. Registered agricultural use sites for imazethapyr ammonium salt include: fallow/idleland I conservationreserve program (CRP), alfalfa, beans (dried-type, succulent, lima), clover, field corn, endive (escarole), garbanzos (including chickpeas), lentils, lettuce, lupine (grain), peanuts, peas (unspecified, dried-type, southern, succulent), rice, soybeans (edible, unspecified), and trefoil. Non-agricultural Use Sites Registered non-agricultural use sites for imazethapyrinclude: rights-of-way (railroad, other), fencerows, hedgerows, uncultivated areas/soils, and ornamental lawns and turf. Registered non-agricultural use sites for imazethapyr ammonium salt include: airports, landing fields, commercial/institutional/ industrial premises and equipment (outdoor), industrial and

2construction areas (outdoor), rights-of-way, fencerows, hedgerows, ornamental lawns and turf, and utilitypoles. 

### FORMULATIONS AND APPLICATION METHODS Imazethapyr is formulated as an emulsifiable concentrate, a soluble liquid concentrate, water dispersible granules, and a wettable powder. Imazethapyr ammonium salt is formulated as soluble liquid concentrate. 

### HISTORY OFIMAZETHAPYR and BEAD PRODUCTS The first herbicide containing imazethapyr was registered in 1990 and the first herbicide containing imazethapyr's ammonium salt was first registered in 1989. Bothproducts were first labeled to control broadleafweeds and grasses in soybeans.
BEAD conducted assessments for two Section 18 emergency exemption requests for use ofthe ammonium salt ofimazethapyr onClearfield rice (resistantto imazethapyr) to control red rice in Louisiana and Texas for the 2001 growing season. In both cases, BEAD found that adequate alternatives existed, which included alternative chemicals and cultural/preventative controls (e.g., crop rotation, cleaning ofmachinery) (Deitrich & Halvorson, 2001a, 2001b). Inthat same year, special local needs (SLN) registrations for imazethapyr were granted to several southern states (including Louisiana and Texas) to control red rice and other grasses and weeds 

### in rice. By 2003, all ofthese SLNs had expired; in 2008, five states (Arkansas, Louisiana, Mississippi, Missouri, and Texas) declared a crisis exemption for the use ofimazethapyrto control red rice on Clearfield rice. The crisis was approved in all five states, but Texas and Arkansas later withdrew their requests. No BEAD reviews were conducted for the crisis exemptions, butthese requests and the earlier SLN registrations could indicate thatthe chemical is preferred by growers for the control ofred rice despite no BEAD finding ofemergency conditions for the 2001 Section 18 requests. The lack ofan emergency situation does notpreclude importance of the requested chemical. 

### USAGE Usage Trends, Agricultural Uses Imazethapyr's annual agricultural usage averaged 441,000 pounds ofactive ingredient (a.i.) per year from 1998-2012. The average total area treated in thattime frame was 8.4 million acres per year; the overall average application rate of0.053 pounds a.i. per acre. Figure 1presents imazethapyr's usage inpounds a.i. overthe 1998-2012 time frame. Figure 2 presents total area treated inacres overthe same timeframe. These showthat, after a deep decrease in usage, imazethapyr's usage has been steadily increasing since 2007. (Proprietary data, 1998-2012).



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### Figure 1. Imazethapyr TotalPounds Active IngredientA lied, 1998-2012 900,000

000\0.-iNMo::tLn\.01' mmoooooooo 0\0\00000000 .-1 .-1 N N N N N N N N Source: ProprietaryData, 1998-2012 oo en o .-1 N 0 0 .-1 .-1 .-1 0 0 0 0 0 N N N N N



### Fi ure2. Imazetha r, Total Area Treated

000\0.-iNMo::tLn\.01' 0\0\00000000 .-1.-iNNNNNNNN Source: ProprietaryData, 1998-2012**~~~::::::::** 00000 NNNNN - Pounds AI

- TAT (acres)

As seen in Table 1, the total usage (lbs A.l. applied) across all crops increased by more than 100,000 lbs annually from the 2003-2007 time frame to the 2008-2012 time frame. Imazethapyr usage incomhas decreased as a percent oftotal usage while usage in rice has increased its share. Usage in soybeans accounted for the largest proportion oftotallbs applied in both time periods.

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# - 2003-2007 2008-2012 Average annuallbs AI applied = 286,000 Average annuallbs AI applied = 408,000 Crop %Lbs Crop %Lbs Soybeans 49 Soybeans 58

Com I9 Rice 32 Rice I9 Alfalfa 3 Alfalfa 7 Com 2 Dry Beans/Pt<as 4 DryBeans/Peas 2 Other* 3 Other* 2 *Othercrops include peas (fresh/green/sweet), peanuts, beans (green, lima), sweet com, and fallow land (2008- 20I2 onl Source: ProprietaryData, 2003-2012 Table 2 shows the proportion oftotal usage inthe top ten states. The top six states for imazethapyr usage are eithertop rice or soybeanproducing states. 

### Table 2. States with HighestUse ofImazethapyr- PercentofTotalPounds Applied, 2008- 2012 Average annuallbs AI applied=408,000 State %Lbs Arkansas IS

Iowa II Nebraska IO Louisiana 9

Indiana 8 Illinois 6 South Dakota 4 North Dakota 4

Kentucky 4 Missouri 4 Other* 23 *Other states with usage in the 2008-20I2 time frame are: South Dakota, North Dakota, Kentucky, Missouri, Minnesota, Wisconsin, Michigan, Mississippi, Texas, Kansas, Ohio, Pennsylvania, Washington, Utah, California, Maryland, Oklahoma, Montana, Virginia, NewMexico, Idaho, North Carolina, South Carolina, Arizona, Delaware, Tennessee, Oregon, Nevada, Georgia, Colorado, Wyoming, and New York. Source: Proprietary Data, 2008-2012
Application Rates and Percent Crop Treated The highest use interms ofpounds A.I. applied and total area treated (TAT) was in soybeans. However, the highest applicationrates were onrice and alfalfa, 0.068 and 0.062lbs A.I. peracre respectively.

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## - Crop Average Annual Average Annual Average AI Rate Pounds AIApplied* TotalAcres Treated** (Lbs Allacre) Soybeans 238,000 4,610,000 0.052

Rice 132,000 1,930,000 0.068 Alfalfa 12,000 200,000 0.060

Com 10,000 240,000 0.042 DryBeans/Peas 10,000 310,000 0.032

Peas, green 3,000 70,000 0.043

Peanuts 2,000 30,000 0.067 *Table includes all crops with average annuallbs applied>1,000 lbs; lbs AI applied is rounded to nearest thousand, TAT is rounded to nearestten thousand **Total Acres Treated (TAT) equals the sum ofall acres treated for a crop; acres that receive multiple treatments are counted multiple times in TAT. Source: EPA Proprietary Data, 2008-2012 Table 4 displays percent crop treated (PCT) estimates for eightcrops for which datawere available. Despite the highest usage in soybeans and rice, the crops with the highest PCT of imazethapyr are greenpeas, rice, dry beans and peas, and greenbeans. Tabl 4 P e 

# . ercen tCrop rea e WI T t d 'th Imaze 

### thapyr, 2004 2011


# - Crop Avera2ePCT Peas, Green 40 Rice 30 Dry Beans/Peas 10 Beans, Green 10 Soybeans 5 Peanuts 5 Alfalfa <2.5 Com <1.0 Source: EPA, 2013, ScreeningLevel Usage Analysis (SLUA) Geographic Distribution oflmazethapvrUse inAgriculture Anothermeasure ofusage is the use intensity. In this analysis, the use intensity is expressed as the average annual amount (inpounds) ofthe active ingredient applied per 1,000 acres ofcrop acres grown. This differs from the applicationrate, which is expressed as the pounds a.i. applied pertreated area. Figure 3 spatially represents imazethapyruse intensity inthe U.S. Use intensity is highest Louisiana and Arkansas, the two states withthe highest rice production. Formore information about this map, see Appendix A.

6Figure3. ImazethapyrUsage by State (2008--2012)

Pounds Active Ingredient per 1.000 Crop Acres Grown CJ No Data CJ<0.5 CJo

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Source: Proprietary Data, 2008-2012. See Appendix A for additional details on this map Non-Agricultural Usage Available non-agricultural usage data for imazethapyr is limited and most are dated. Data available from the USDANASS Chemical Use Survey shows that, inthe year 2006, imazethapyr was applied to 1percent offloriculture operations in Florida; there was also use in Michigan floriculture operations, but the percentage was notreported because itwas less than 0.5 percent. The ammonium salt was applied to 12 percent ofpropagative material infloriculture operations in Michigan in the same year. (USDANASS Chemical Use Survey, 2006) Older non-agricultural usage data for reports approximately 324 lbs a.i. ofimazethapyr were applied inlandscaping in 1999, which accounted for less than 1% oftotallbs a.i. ofherbicides applied inthat sector. More recent data suggests showed that approximately 750 lbs a.i. of imazethapyr were applied by lawn care operators and another 440 lbs were applied to golf courses in 2011. Again, these amounts accounted for less than 1percent oftotallbs a.i. of herbicides applied in both sectors. (Proprietary data, 1999, 2012). Databetweenthese years were not available to EPA.

7CHEMICAL AND USE CHARACTERISTICS Imazethapyr is inthe Weed Science Society ofAmerica (WSSA) herbicide mechanism ofaction group 2 which is a group ofherbicidesthat inhibitthe production ofthe key plant enzyme acetolactate synthase (ALS). The mode ofaction is characterized by growthinhibition, chlorosis and necrosis with death occurring over a period ofweeks. Imazethapyr is an herbicide that is used preplant incorporated orbroadcast preemergence and/or postemergence to control annual broadleafand annual grass weeds. Imazethapyr is applied in many crops with the majority ofthe herbicide being used in soybeans, rice, alfalfa, com, and dry beans/peas (Table 3). However, it is important to note that the crops with the highest PCT of imazethapyr are greenpeas, rice, dry beans and peas, and green beans (Table 4). Rice,justas with com, is not naturally resistant to this herbicide therefore imazethapyr can only be used in imidazolinone tolerant varieties.

ROLE OF IMAZETHAPYR IN PEST MANAGEMENT Imazethapyr is used to manage some difficult to control weeds including many annual broadleaf weeds in greenpeaproduction as well as grass weeds in rice production. The control ofthese two weed types is very importantto sustainingthe yield and quality ofthese crops. With over 40% ofthe United States greenpeacrop and 30% ofthe rice crop being treated with this herbicide, imazethapyr would seem to have an important role in weed control in the production ofthese two crops. Green peas are highly sensitive to weed competition and as such aggressive weeds such as common lambsquarters (Chenopodium album) are considered serious impediments to yield quality and quantity (Krall et al., 2014). Because greenpeas are naturally resistant to the herbicide imazethapyr it is safe to use as a preplant incorporated or preemergence herbicide for the control ofweeds. Efficacy for the control ofbroadleafweeds inthe production ofgreenpeas is sufficient enough that imazethapyr is considered in some states as "

...the most widely used herbicide to control broadleafweeds." (Dudley et al., 2000).
In the case ofrice production, red rice (Oryza sativa) is problematic intwo ways. First, like many other crops, the production ofrice has its problems with weeds which compete for resources. Second, similarto othermany grain crops, the harvested portion can become contaminated with weed seeds. The red color ofthe seed ofred rice is a problem inthe harvested rice because it causes a red discoloration to the milled product when it gets harvested with the desired grain (Webster and Levy, 2012). While useful in controlling some difficultto control weeds, as stated above, there are more than a dozen weed species that have biotypes which are resistant to imazethapyr, some ofthe species include weeds that are difficult to control such as Palmer amaranth (Amaranthuspalmeri), commonwaterhemp (Amaranthus tuberculatus) and Kochia (Kochia scoparia), among others. These weed species are among the most problematic and pervasive weeds in crop production and are prolific seed producers. However, despite the number ofweed biotypes that are resistant to
8this herbicide, there are some difficultto control broadleafand grass weeds that are controlled by this herbicide. Whenused in combination with other herbicides, imazethapyr is an important tool inthe production ofsome crops such as green peas and rice, which appears to be due, at least in part, to natural tolerance and engineeredresistance in the host crops. 

### DATA NEEDS The Agency currently does nothave important information on imazethapyr. Obtaining usage information for the following sites may improve future assessments conducted by the Agency related to the use and importance ofimazethapyr: Agricultural usage data for: endive, minorlegume crops (e.g., lentils), clover, and lupine NonAgricultural usage data and use information for: industrial areas, rights-of-way, CRP land, and/or any registered use sites that are ofimportance to users Usage information on crops with low usage but importantniche markets for irnazethapyr. Usage data includes poimds applied, percent crop treated, application rates andtiming, methods ofapplication, target orniche pests.



### REFERENCES Deitrich, V. and A. Halvorson. 2001a. Review ofRequest for Emergency Exemption for Use of Imazethapyr on Clearfield Rice to Control Red Rice in Louisiana (01-LA-02). Deitrich, V. andA. Halvorson. 2001b. Review ofRequest for Emergency Exemption for Use of Imazethapyr onClearfield Rice to Control Red Rice in Texas (01-TX-04). Dudley, R., S.J. Fuchs, arnd R. Hirnyck. 2000. Crop Profile for Peas (Green) in Idaho. Online. Internet. August 14th, 2013. EPA. 2013. Irnazethapyr (128922) Screening Level Usage Analysis (SLUA). Biological and Economic Analysis Division, Office ofPesticide Programs, US Environmental Protection Agency. March4, 2013. Gillespie, W.E., G.F. Czapar, and A.G. Hager. 2011. Pesticide fate inthe environment: a guide for field inspectors (Contract Report 2011-07). Illinois State Water Survey, Institute of Natural Resource Sustainability, University ofIllinois at Urbana-Champaign. Champaign Illinois. Heap, I. The International Survey ofHerbicide Resistant Weeds. Online. Internet. Wednesday, August 14th, 2013. Available Krall, J.M., S.D. Miller, J.T. Cecil, C. Bastian, T. Foulke, D.D. Baltensperger, B.M. Harveson, P.A. Burgener, G.W. Hergert, G.L. Hein, D.J. Lyon, T. Nleya, J. Rickertsen and S. Blodgett. Peaproduction in the high plains. South Dakota State University Extension Fact Sheet FS932. Available at ianrpubs.unl.edu/live/ec187/build/ec187.pdf, Accessed January Proprietary Data. 1998-2012.

9Senseman, S. 

### ed. 2007. Herbicide HandbookNinth Edition. Lawrence, KS: Weed Sci. Soc. of America

. USDA NASS. Chemical Use Surveys, 2006 and 2009. http://www.nass.usda.gov/Surveys/Guide to NASS Surveys/Chemical Use/#description Webster and Levy 2012. Rice Production Handbook. Chapter 5 Weed Management.

10APPENDIX A The map included herein is primarily for the use ofthe risk assessors inthe Environmental Fate and Effects Division. The map provides a very broad geographical view ofthe amount (in pounds) ofthe active ingredient applied per 1,000 acres of"landin farms". These data are included inthe maps because risk assessors are interested inthe amount ofa pesticide used across farmland. Because ofthe definition ofLand in Farms, as discussed below, the calculated valuespresented inthe map are not equivalentto an application rate (lbs ai/A). The dataused to make these maps have many limitations. Any interpretation ofthe maps should considerthe underlying data and the associated limitations carefully. The smallest areas shown onthe maps within each state are Crop Reporting Districts (CRD). CRDs are definedbyUSDA and each consists ofmultiple 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 surveythat samples every county in the United States, the use ofCRDs allow for a sample to be collectedthat represent a much larger area with relatively homogeneous agricultural characteristics. The numerator (annual average pounds applied) is based onprivate market surveys ofpesticide use in agriculture averaged overthe last five years (Proprietary Data, 2007-2011). These surveys cover about 60 crops and are targeted in states that produce the majority ofthe crop. Although the surveys capture most ofthe use ofa particular active ingredient in agriculture, there are several limitations to these surveys:

• States with minorproduction ofa surveyed crop are not sampled. • Not all types ofpesticides are surveyed in every crop in every year. • Many specialty crops with very small acreages are not included in the survey. The result ofthese limitations is that CRDsthat showno usage may actually have a small amount ofthe active ingredientbeing used.

11The denominator (1,000 Acres ofland infarms) was selected from the Census ofAgriculture (USDA, 2007) to represent agricultural acreage that is actively managed and includes most ofthe areas treated withpesticides. The category "Land in Farms" is defined bythe Census of Agriculture as being made up offour components: I) Total cropland, 2) Permanentpasture, 3) Total woodland, 4) Land in farmsteads, buildings, livestockfacilities, ponds, roads, wasteland, etc. This category includes land inthe various USDA conservationprograms. Itshould be noted that the Census ofAgriculture does not include grazing land rented (on a per-animal basis) from the Bureau ofLand Management orForest Service, thus it is an underestimate ofthe land being managed for agricultural purposes. The reader should payparticular 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 ofmeasurement do matter and may be different between maps.

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