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

### MAR 10 ZC14

MEMORANDUM OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

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

# Agronomist**~** Biological Analysis

## Branch**~V** Rafael A. Prieto. Environmental Protection Specialist 

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# /Q.", r/7 Science Information and Analysis Branch 

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THRU: Michelle Ranville, Economist

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### ~-J~J Biological and Economic Analysis tvision (7503P)
Arnet Jones, Chief Biological Analysis Branch
Diann Sims, Chief Science Information and Analysis Branch Timothy Kiely, Chief

# /J1~}(_a)**~** Economic Analysis Branch Biological and Economic Analysis Division (7503P) TO: Katherine St. Clair, Chemical Review Manager Risk Management and ImplementationBranch 2 Pesticide Re-evaluation Division (7508P)



### Peer Review Panel date: February 5, 2014

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### SUMMARY Imazethapyr is an imidazolinone herbicide that inhibits the production ofthe keyplant enzyme acetolactate synthase (ALS). Itis usedpreplant incorporated, preemergence, orpostemergence to control annual broadleafweeds and annual grasses. Based on the percent crop treated, the two crops withthe highest percentage ofuse are greenpeas andrice. With over40% and 30%, respectively, ofthe crops receiving applications ofimazethapyr, it is clearthat there is an important use for this herbicide inthose crops. Althoughthere are more than a dozen weed species thathave biotypes which are resistantto imazethapyr, this herbicide, in combination with others, seems to be ofparticularimportance for controlling some difficult to control broadleaf and grass weeds in greenpeaand rice production. 

### In addition, imazethapyr may be an important tool for managing weeds in anintegrated weedmanagementprogram. 

### INTRODUCTION
The Biological and Economic Analysis Division (BEAD) Chemical Profile (BCP) provides an overview ofthepest management roles and quantitative usage information for imazethapyr and its ammonium salt. The BCP includes summaries ofprevious BEAD products and available public and/orprivate use and usage datafor imazethapyrto describe the role ofthis chemical in pest management. Additional information onuse is available inthe imazethapyr Label Data Report. Informationprovided inthis BCP may be usedby stakeholders (e.g., users and registrants), OPP risk assessors, OPP risk managers, and the general public during the Registration Reviewprocess for this pesticide. 

### USE SITES Agricultural Use Sites Registered agricultural use sites for imazethapyr include: fallow/idleland /conservation reserve program (CRP), alfalfa, beans (dried-type, succulent, lima), clover, com (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 conservation reserve program (CRP), alfalfa, beans (dried-type, succulent, lima), clover, field com, 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 imazethapyr include: 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/ institutionaV industrial premises and equipment (outdoor), industrial and

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### construction areas (outdoor), rights-of-way, fencerows, hedgerows, ornamental lawns and turf, and utility poles. 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 OF IMAZETHAPYR 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 exemptionrequests for use ofthe ammonium salt ofimazethapyr on Clearfield rice (genetically engineered to withstand imazethapyr) to control red rice inLouisiana 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). In that 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 inrice. By 2003, all ofthese SLNs had expired; in 2008, five states (Arkansas, Louisiana, Mississippi, Missouri, and Texas) declared a crisis exemption for the use ofimazethapyr to control red rice on Clearfieldrice. The crisis was approved in all five states, but Texas and Arkansas later withdrewtheir requests. No BEAD reviews were conducted for the crisis exemptions, butthese requests and the earlier SLN registrations could indicate that the chemical ispreferred by growers for the control ofred rice despite no BEAD finding of emergency conditions for the 2001 Section 18 requests. The lack ofan emergency situation does not preclude importance ofthe 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 that time frame was 8.4 million acres per year, and the overall average application rate was 0.053 pounds a.i. per acre. Figure 1presents imazethapyr's usage in pounds a.i. overthe 1998-2012 time frame. Figure 2 presents total area treated in acres 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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### Fi re 1. 

### Imazetha 900,000

0**~** m o**~** N m**~ ~** **~ ~** **~** m o**~** N**mmoooooooooo~~~** mmooooooooooooo**~ ~**  N N N N N N N N N N N N N Source: Proprietary Data, 1998-2012 

### Fi ure 2. Imazetha r, TotalArea Treated**~mo~Nm~~~~~mo~N mmoooooooooo~~~**  mmooooooooooooo**~~NNNNNNNNNNNNN** Source: Proprietary Data, 1998-2012 

### lied, 1998-2012

- Pounds AI

- TAT (acres)



### As seeninTable 1, the average annual usage (lbs A.

### I. applied) across all crops increased by more than 100,000 lbs from the 2003-2007 time frame to the 2008-2012 time frame. Imazethapyr usage in comhas decreased as a percent oftotal usage while usage inrice has increased its share. Usage in soybeans accounted for the largest proportion oftotallbs applied in both time periods.



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### T bl 1 P rti 

### fl th 

### p d A 

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## c 2003 2012 a e 

# . ropo 000 

### maze apyr ouo s •PPJie ,y rop, 

# - 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 19 Rice 32 Rice 19 Alfalfa 3 Alfalfa 7 Com 2 Dry Beans/Peas 4 Dry Beans/Peas 2 Other* 3 Other* 2 *Other crops include peas (fresh/green/sweet), peanuts, beans (green, lima), sweet com, and fallow land (2008- 2012 onl Source: ProprietaryData, 2003-2012 

### Table 2 shows the proportion oftotal usage inthe top ten states. The top six states for imazethapyrusage are either top rice or soybean producing states. 

### T bl 2 P

a e 

# . ropo

### rf 1000 

### flmaze th

### apyr

### p d Applied by 

### State, 2008-2012 ouo s Average annuallbs AI applied=408,000 State %Lbs Arkansas 18

Iowa 11 Nebraska 10 Louisiana 9

Indiana 8 Illinois 6 South Dakota 4 North Dakota 4

Kentucky 4 Missouri 4 Other* 23 *Other states with usage in the 2008-2012 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 application rates were onrice and peanuts, 0.068 and 0.067lbs a.i. per acre, respectively. (Table 3)

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### T bl 3 I a e 

# . mazethapyr

# u p se: d 

### TAT oun s, , and A R t 2008 2012* vg 

### a e, 

# - Crop Average Annual Average Annual Average AI Rate Pounds AI Applied* TotalAcres Treated** (Lbs Al/acre) 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 Dry Beans/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 nearestthousand, TAT is rounded to**n~arest** ten 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: EPAProprietaryData, 2008-2012 

### Table 4 displays percent crop treated (PCT) estimates for eight crops for which data were available. Despite the highest proportion ofusage in soybeans and rice, the crops withthe highest PCT ofimazethapyr are greenpeas, rice, dry 

### beans and peas, and green beans. 

### Tabl 4 P e 

# . ercen rop rea e WI 

### maze apyr, 

# - tC 

### T t d 'thI th 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 Analysts (SLUA) 

### Geographic Distribution ofImazethapvr Use in Agriculture
Another measure ofusage is the use intensity. Inthis analysis, the use intensity is expressed as the average annual amount (in pounds) ofthe active ingredient applied per 1,000 acres ofcrop acres grown. This differs from the application rate, which is expressed as the pounds a.i. applied pertreated area. Figure 3 spatiallyrepresents imazethapyr use intensity in the U.S. Use intensity is highest Louisiana and Arkansas, the two states with the highest rice production. For more information about this map, see Appendix A.



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### Figure 3. ImazethapyrUsage by State (2008-2012)

Pounds Active Ingredient per 1,000 Crop Acres Grown 

### c:::::J No Data 0 <0.5 c=J o.5-1.5

. 1.5-3 

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Source: ProprietaryData, 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 USDA NASS Chemical Use Survey shows that, in the year 2006, imazethapyr was applied to 1percent offloriculture operations in Florida; there was also use in Michigan floriculture operations, butthe percentage was notreported because it was less than 0.5 percent. The ammonium salt was applied to 12 percent ofpropagative material in floriculture operations in Michigan inthe same year. (USDANASS Chemical Use Survey, 2006) Older non-agricultural usage data for reports approximately 324lbs a.i. ofimazethapyr were applied inlandscaping in 1999, which accounted for less than 1% oftotallbs a.i. ofherbicides applied in that sector. More recent data suggests showed that approximately 750 lbs a.i. of imazethapyr were applied bylawn 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 ofherbicides that inhibit the production ofthe key plant enzyme acetolactate synthase (ALS). The mode ofaction is characterized by growth inhibition, chlorosis and necrosis with death occurring overa period ofweeks. Imazethapyr is an herbicide that is used preplant incorporated orbroadcastpreemergence and/or postemergence to control annual broadleafand annual grass weeds. Imazethapyr is applied in many crops with the majority ofthe herbicide beingused in soybeans, rice, alfalfa, com, and dry beans/peas (Table 3). However, itis important to note thatthe crops with the highest PCT of imazethapyr are greenpeas, rice, dry beans and peas, and green beans (Table 4). Rice,justas with com, is notnaturally resistant to this herbicide therefore imazethapyr can onlybe used in genetically modified (GM) orimidazolinone tolerant varieties.

ROLE OF IMAZETHAPYRIN 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 important to sustaining the yield and quality ofthese crops. With over 40% ofthe United States greenpeacrop and 30% ofthe rice crop being treated withthis herbicide, imazethapyr would seemto have an important role inweed control inthe production ofthese two crops. Greenpeas 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 preplantincorporated orpreemergence herbicide for the control ofweeds. Efficacy for the control ofbroadleafweeds inthe production ofgreen peas is sufficient enoughthat 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) isproblematic intwo ways. First, like many other crops, the production ofrice has its problems withweeds which compete for resources. Second, similarto many other grain crops, the harvested portion can become contaminated with weed seeds. The red color ofthe seed ofredrice is a problem inthe harvestedrice because it causes a red discoloration to the milledproduct when it gets harvested withthe desired grain (Webster and Levy, 2012).
While useful incontrolling some difficult to control weeds, as stated above, there are more than a dozen weed species that have biotypes which are resistantto 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 seedproducers. However, despite the number ofweed biotypes that are resistant to

8this herbicide, there are some difficult to control broadleafand grass weeds that are controlled by this herbicide. Whenused in combination with otherherbicides, imazethapyr is an important tool in the production ofsome crops such as greenpeas andrice, which appears to be due, at least inpart, to natural tolerance and engineered resistance inthe host crops. DATA NEEDS The Agency currently does not have important information onimazethapyr. Obtaining usage information for the following sites may improve future assessments conductedbythe Agency related to the use and importance ofimazethapyr: Agricultural usage data for: endive, minorlegume crops (e.g., lentils), clover, and lupine Non Agricultural 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 oncrops with lowusage but important niche markets for imazethapyr. Usage data includes pounds applied, percent crop treated, application rates and timing, methods ofapplication, target orniche pests.



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### 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. and A. Halvorson. 2001b. Review ofRequest for Emergency Exemption for Use of Imazethapyr on Clearfield Rice to Control Red Rice in Texas (01-TX-04). Dudley, R., S.J. Fuchs, amd R. Hirnyck. 2000. Crop Profile for Peas (Green) inIdaho. Online. Internet. August 14th, 2013. EPA. 2013. Imazethapyr (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 inthe highplains. SouthDakota State University Extension Fact Sheet FS932. Available at ianrpubs.unl.edullive/ec187/build/ec187.pdf, Accessed January Proprietary Data. 1998-2012. Senseman, 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 primarilyfor the use ofthe risk assessors in the 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"land in farms". These data are included in the maps because risk assessors are interested in the amount ofa pesticide used across farmland. Because ofthe defmition ofLand in Farms, as discussed below, the calculated values presented in the map are not equivalent to an application rate (lbs ail A).
The data used to make these maps have many limitations. Any interpretation ofthe 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 ofmultiple counties thathave 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 inthe United States, the use ofCRDs allow for a sample to be collectedthatrepresent a much larger area with relatively homogeneous agricultural characteristics.
The numerator (annual average pounds applied) is based on private 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 thatproduce the majority ofthe crop. Although the surveys capture most ofthe use ofa particular active ingredientin agriculture, there are several limitations tothese surveys:

• States with minor production 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 CRDs that show no usage may actually have a small amount ofthe active ingredient being used.
The denominator (1,000 Acres ofland in farms) was selected from the Census ofAgriculture (USDA, 2007) to represent agricultural acreage that is actively managed and includes most ofthe areas treated with pesticides. The category "Land in Farms" is defined by the Census ofAgriculture as being made up offour components: 1) Total cropland, 2) Permanentpasture, 3) Total woodland, 4) 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 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. Thereader 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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