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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D

. C. 20460



### MAR 14 2014

OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION

MEMORANDUM

SUBJECT:

FROM:

THRU: BEAD Chemical Profile for Registration Review: Imazapyr (128821) and Imazapyr, Isopropylamine salt (128829)

Sunil Ratnayake, Biologist

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# · t**~** Biological Analysis Branch 

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1 Cynthia Doucoure, Environmental Protection Specialis t 

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,**~** Science Information and Analysis Branch

Derek Berwald, Economist 

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Economic Analysis Branch \ ,J

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Biological and Economic Analysis Division (7503P)

Arnet Jones, Chief Biological Analysis Branch

Diann Sims, Chief

Science Information and Analysis Branch

Timothy Kiely, Chief 

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Biological and Economic Analys1s Division 03P)

TO: Joel Wolf, Chemical Review Manager

Risk Management and Implementation Branch V

Pesticide Re-evaluation Division (7508P)

Product Review Panel date: February 5, 2014

Page 1 ofllPage 1 of 11 OFFICE OF CHEMICAL SAFETY

AND POLLUTION PREVENTION UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

MEMORANDUM

SUBJECT: BEAD Chemical Profile for Registration Review: Imazapyr ( 128821 ) and

Imazapyr, Isopropylamine salt ( 128829 )

FROM: Sunil Ratnayake , Biologist

Biological Analysis Branch

Cynthia Doucoure, Environmental Protection Specialist

Science Information and Analysis Branch

Derek Berwald , Economist Economic Analysis Branch Biological and Economic Analysis Division (7503P)

THRU: Arnet Jones, Chief

Biological Analysis Branch

Diann Sims , Chief Science Information and Analysis Branch

Timothy Kiely, Chief Economic Analysis Branch Biological and Economic Analysis Division (7503P)

TO: Joel Wolf

, Chemical Review Manager

Risk Management and Implementation Branch V

Pesticide Re

- evaluation Division (7508P)

Product Review Panel date: Fe b ruary 5, 2014Page 2 of 11

SUMMARY

Imazapyr technical ingredient was first registered in the U.S. in 198 5 (USEPA, 2006). Imaza pyr (imazapyr and the isopropylamine salt of imazapyr ) is a non

- selective systemic herbicide registered for use as pre and post

- emergent treatments to control broad spectrum of terrestrial and aquatic weeds

. This includes terrestrial annual and perennial grasses, broadleaf weeds, herbs, woody species, and riparian and emergent, aquatic weed species

. In addition , imazapyr plays a major role on controlling grasses and broadleaf weeds in Clearfield ® production systems where the crop is tolerant to imidazolinone herbicides. Imazapyr belongs to the family of

imidazolinone herbicides and this herbicide provides an effective and broad spectrum of weed

control at lower rates than many other herbicides. Imaza pyr is quickly absorbed through foliage, stems, and roots and rapidly translocated through the plants. The mode of action of this

herbicide is inhibition of the aceto lactat e synthase (ALS) which is an enzyme involved with the biosynthesis of branch ed

- chain amino acids such as leucine, isoleucine, and valine in plant species

. Growth of treated plants stops within one to three weeks after the application. In the United States, 144 weed species have developed resistance to different modes of action of

herbicides

. Of these resistant weeds, biotypes of 46 weed species have developed resistance to

the mechanism of action of imidazolinone herbicides

. Of these we eds, only 4 weed species have shown resistance to imazapyr and cross resistance to other ALS inhibiting herbicides

.

Based on private market u sage data from 1998

- 2012, the highest usage of imazapyr was observed during the year 2002 and since then

, a declin e in usage is observed in all the states for

which data are available

. Over the last five years it has been applied to less than 300,000 acres annually and on less than 1% of corn and pasture acreage

. Wider acceptance of glyphosate

tolerant crops may hav e contributed to the reduction of usage of imazapyr in the United States.

Imazapyr and imazapyr isopropylamine salt do not appear to have a major role in traditional agriculture, based on use data. Use data is unavailable on many other uses, however, especially in forestry sites, aquatic areas and non

- agricultural uses. Imazapyr and imazapyr isopro pylamine salt may be important for weed control in these situations.

INTRODUCTION

T he 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 rev iew. The anticipated audience consists of the team of EPA staff currently evaluating the registration status

of imazapyr and the isopropylamine salt of imazapyr , and eventually the general public. This document builds upon the data BEAD provides in the Lab el 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 January 2014

.Page 3 of 11

HISTORY OF ASSESSMEN TS FOR IMAZAPYR

The t echni cal ingredient of i mazapyr was first registered in the U.S. in 198 5 (USEPA, 200 6 ).
However, a non

- crop end use product had been previously registered in July 1984 and the first food use on corn was registered in 1997. Subsequently, t he aquatic and grassland uses were register ed in 2003(Imazapyr Chemical Fact Sheet, 2012). Currently there are 24 tolerances listed in 40 CFR § 180.500 for residues of the herbicide imazapyr, applied as the acid or isopropylamine salt

.

Other than usage reports, BEAD has not assessed the importance or benefits of imazapyr. Although imazapyr was reregistered in 2006, BEAD did not evaluate the importance of imazapyr as part of that process.

BEAD prepared a Screening Level Usage Analysis (SLUA) in April 2013 that provid ed data on reported agricultural uses o f imazapyr on corn and pastureland in the U.S. from 2004

- 201 1 . The SLUA reported that an average of 9 ,00 0 pounds of imazapyr active ingredient ( a.i. ) was a pplied annually on corn and an average of 2,000 pounds a.i. w as applied on pastureland. The average percent crop treated for both uses was <1 %.

COMMON FORMULATIONS AND APPLICATION METHODS

Imazapyr is commonly formulated as a soluble and emulsifiable concentrates , wettable powder,

and water dispersible granules

. The isopropylamine salt of imazapyr is commonly formulated as aqueous and ready

- to

- use solutions

. Imazapyr and isopropylamine salt of imazapyr are applied

as a ground application using handheld equipment (backpack sprayers, sprinkling cans, han dgun sprayers, high

- pressure handwand sprayers) or granular broadcast applications using push

- type or backpack spreaders

. They can also be applied as an aerial spray.

USE SITES

Agricultural Use Sites: Imazapyr is registered for use on field corn and imazapyr and the isopropylamine salt of imazapyr are registered for use on conifer plantations, forestry sites, and grass pastures and rangelands , as well as agricultural non

- crop areas.

Non

- Agricultural Use Sites:

I mazapyr and the isopropylamine salt of imazapyr are registered for use on wildlife openings,

non

- agricultural non

- crop areas, animal housing premises (outdoor), outdoor residential areas (paved ar e as, driveways, patios, etc.), recreational areas, commercial/institutional/industrial

areas, and in aquatic s ites (ponds, lakes, streams, etc.). They are also used on established turfgrass on industrial grounds, athletic fields, cemeteries, parks, golf course roughs, and institutional grounds.Page 4 of 11

IMAZAPYR USAGE

Agricultural Usage Trend

According to proprietary market research surveys, reported use of imazapyr in the U.S . peaked in

2002 and has decreased substantially in terms of pounds a.i. applied and total area treated since then, as shown in Figures 1 and 2. The overall average a.i. rate of a pplication during this period

was 0.0 15 lbs a.i. per acre.

Figure 1. Imazapyr Agricultural Usage : Pounds AI Applied

, 1998

- 201 2

Source: EPA Proprietary Data, 200 2

- 201 2

0 40,000

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 Pounds A.I. Applied

YearPage 5 of 11

Figure 2: Imazapyr Agricultural Usage: Total Area Treated Applied , 1998

- 2012

Source: EPA Proprietary Data, 200 2

- 201 2

Agricultural Usage Trend: Top Crops, 2003

- 2012

Reported use of imazapyr decreased on corn and pastureland during the 2003

- 2012 time frame.

As shown in Table 1 , the average annual pounds a.i. applied on all crops decreased by 86% from 19,600 lbs a.i during the earlier period ( 2003

- 2007 ) to 2,700 lbs a.i. in the more recent period (2008

- 2012). Application rates for pasture are higher than for corn, and the avera ge a.i. rate across all crops is closer to corn, because corn is a much larger use (71% of the total pounds a.i. applied from 2008

– 2012). Between the two periods shown in Table 1, the application rate changed little for corn, but more than doubled for pasture uses , although this may be an artifact of small sample sizes in the use survey

.

0 3,000,000

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

YearPage 6 of 11

Table 1

. Imazapyr Top Crops : Comparison of Usage between the 2003

- 2007 and 2008

- 2012

Timeframes.

2003

- 2007

Av g Annual Lbs A.I. Applied = 19,6 00 2008

- 2012

Av g Annual Lbs A.I. Applied = 2,7 00

Crop Proportion of

Total Lbs A.I. of Imazapyr Applied Avg. A.I. Rate

of Application (lb/acre) Crop Proportion of

Total Lbs A.I. of Imazapyr Applied Avg. A.I. Rate of

Application (lb/acre)

Corn 83 % 0.013 Corn 71 % 0.012

Pastureland 16 % 0.21 Pastureland 29 % 0.471

Other* 0.2 0.050
*Other crop includes dry beans/peas; however, no active registration was found for this use. Source: Proprietary Data, 2003

- 2012

Agricultural Usage Trend: Top States, 2003

- 2012

R eported use of imazapyr decreased in all states during this period

. As shown in Table 2, the average annual pounds a.i. applied i n all states decreased by 86% from 19,600 lbs a.i during the earlier period (2003

- 2007) to 2,700 lbs a.i. in the more recent period (2008

- 2012). The average a.i. rate of application in recent years was high er for Texas (0.50 lbs a.i./acre ) than the overall

national average a.i. rate (0.15 lbs a.i./acre) , reflecting use on pasture s only

. Tennessee is also high er than the national average, but not dramatically so, reflecting use on corn and pastures. Indiana, Kentucky, and Illinois average application rates were lower than the national average, reflecting use on corn only

.

Table 2 . Comparison of States wit h Highest Use of Imazapyr

– Percent of Total Lbs. Applied b etween
the 2003

- 2007 and 2008

- 2012 Timeframes

2003

- 2007

Av g Annual Lbs A.I. Applied = 19,6 00 2008

- 2012

Av g Annual Lbs A.I. Applied = 2,7 00

State Proportion

of Total

Lbs A.I. of Imazapyr Applied Avg. A.I. Rate of

Application (lb/acre) State Proportion

of Total

Lbs A.I. of Imazapyr Applied Avg. A.I. Rate of

Application (lb/acre)

Illinois 19 0.014 Indiana 26 0.012

Indiana 17 0.014 Kentucky 21 0.011

Arkansas 15 0.214 Texas 19 0.500 Kentucky 10 0.013 Illinois 9 0.014

Iowa 8 0.013 Tennessee 8 0.019

Kansas 7 0.014 Other** 17 0.025

Other* 24 0.014

* Other States in the 2003

- 2007 timeframe include AL, CO, MI, MN, MS, MO, MT, NE, NC, ND, OH, PA, SC, SD, TN, TX, UT, VA, WV, WI, and WY.

* * Other States in the 2008

- 2012 timeframe include AL, AR, FL, IA, MI, MS, MO, NE, OH, SC, SD, and VA. Source: Proprietary Data, 200 3

- 201 2Page 7 of 11

Agricultural Use Intensity of Imazapyr Use in the U.S.

Another measure of usage is the agricultural use intensity. I n 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 treate d area. Figure 3 spatially represents imazapyr’s use intensity in the U.S. on corn and pastureland from 2008

- 2012 , which is relatively greater in Kentucky and

Indiana . This is probably due to relatively high share of total use that is on corn, and becau se these two states combine for 47% of the total agricultural imazapyr use. Note that use in Kentucky and Indiana are only high relative to imazapyr use in other states. The average application rate in Indiana is 0.012 lbs a.i. per acre (Table 2), which would imply 12 lbs a.i. per 1,000 treated acres. Use over all cropped acres, however, is a small fraction of a pound. Viewed another way, this measure of intensity implies about three treated acres out of every 1,000 acres of cropland. For more informat ion about this map, see Appendix A.

Figure 3 . Annual A verage A gricultural U se I ntensity of Imazapyr (2008

- 2012).

(Source: Proprietary Data , 2008

- 2012 )Page 8 of 11

Non

- A gricultural Usage

BEAD reviewed available data sources and found that imazapyr was reported to be used on institutional turf (1,800 lbs a.i. applied in 2011) and by Lawn Care Operators (2,430 lbs a.i. applied in 2011). These numbers seem small, but imazapyr is applied at low rates, and they represent roughly 50% more than the amount of imazapyr used for agriculture. BEAD has no data on what may be important uses of imazapyr to control woody plants in forest settings and in

other non

- agricultural area.

Imazapyr is reported to be widely used as an aquatic herbicide in Florida for control of aquatic

weeds and woody species growing in water (Univ. of Florida, 2014). However

, BEAD has no information about the amount of imazapyr applied for such uses.

BIOLOGICAL ASPECTS RELEVANT TO IMAZAPYR

Imaza pyr i s a non

- selective systemic herbicide registered to use as a pre and post

- emergent
herbicide f

or control a broad spectrum of terrestrial and aquatic weeds, including terrestrial annual and perennial grasses, broadleaf weeds, herbs, woody species, and riparian and emergent, aquatic weed species.

. In addition, imazapyr plays a major role on controlling grasses and

broadleaf weeds in Clearfield ® production systems where the crop is tolerant to imidazolinone

herbicides. Clearfield ® crop varieties were developed u sing traditional breeding techniques and they are not considered as genetically modified organisms or GMO products (Colquhoun, et al.,

20 03 ). I maza pyr belongs to the family of imidazolinones or group 2 herbicides (ALS inhibitors) (WSSA, Undated )

. Herbicides in this family are applied at very low rates and have a longer period of residual activity compared to many other herbicides

. Imazapyr is absorbed through roots and foliage and rapidly translocated through out the plants

T he mechanism of action of imidazolinone herbicides is inhibition of the enzyme aceto lactate synthase (ALS) which is also called the acetohydroxyacid synthase (AHAS). It is an enzyme involved with the biosynthesis of branched chain amino acids such as leucine, isoleucine, and

v aline ( WSSA, Undated )

. Other major classes of herbicides which inhibit this enzyme are sulfonylaminocarbonyltriazolinones, pyrimidinylthiobenzoates, sulfonylureas, and triazolopyrimidines ( Colquhoun et al., 2013). Variations i n residual activity, crop sel ectivity,

and the spectrum of weeds controlled may be observed with the application of herbicides included in these classes (Univ. of Tennessee, Undated ). Generally, injury symptoms due to applications of ALS inhibitors appear within a week after the herbi cide treatment. Significant symptoms are chlorosis, purple leaf veins, and bottlebrush appearance of roots in some weed species. Complete death of susceptible weeds may occur within two to three weeks after the herbicide applications. Due to the activity of imaza pyr, susceptible weeds stop growing and

either die or become non

- competitive with the crop planted in the field s

.

It has been reported that in the United States, 144 weed species have developed resistance to

different modes of action of herbicide s. Of these resistant weeds, biotypes of 46 weed species have developed resistance to the mechanism of action of imidazolinone herbicides. Of thesePage 9 of 11

weeds, only 4 weed species have shown resistance to imazapyr and cross resistance to other ALS inhibiting he rbicides (WSSA, Undated). This is primarily due to the extensive use of many ALS inhibiting herbicides for weed management in agricultural and non

- agricultural sites in the

United States

. Weed species with resistance to imidazolinone s can be managed by tank

- mixing

imidazolinone s with other herbicides with different modes of action

.

ROLE OF IMAZAPYR IN PEST MANAGEMENT

Imazapyr does not appear to have a major role in traditional agriculture. Imazapyr ’s use o n corn to control broadleaf and annual weeds, as well as sedge has decreased dramatically to the extent that in recent years, less than 1% of the corn acreage is treated with imazapyr. According to a USDA ERS publication, currently 85% of c or n acreage in the U.S. is planted with Roundup ready corn va rieties (USDA ERS, 2013)

. Adoption of glyphosate toleran t corn varieties has

increased the use of glyphosate and reduced the use of other herbicides in corn production. This explains the little usage of imazapyr in the corn production. On the other hand, use of i maza pyr and imazapyr isopropylamine salt on rangeland and pastureland is increasing , especially in

Texas ; however, the increase in pounds a.i. applied have not resulted in increases in the percent crop treated, which on average was also less than 1%.

I maza pyr is also reported in private market research to play a minor role in the management of broad spectrum weeds in institutional turf and lawns. The role of imazapyr in other registered

use sites such as agricultural and non

- agricultural unculti vated areas
, outdoor residential sites, animal housing premises, commercial/institutional/industrial, and recreational areas, as well as aquatic sites are not as clear as there is no available data

. However, a literature search shows that imazapyr is used in the state of Florida to control aquatic weeds such as torpedograss ( Panicum

repens ) and woody species growing in water, such as melaleuca ( Melaleuca quinquenervia ). Imazapyr also used for the control of floating

- weed species where it is mixed with low concentrations of glyphosate (Univ. of Florida, 20 11 ). Currently, development of resistance in aquatic weeds for imazapyr is not reported in Florida.

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

IMAZAPYR

The Agency currently does not have important information on imazapyr and imazapyr isopropylamine salt . Obtaining the following usage information may improve future assessments conducted by the Agency related to the use and importance of imazapyr and imaza pyr isopropylamine salt :

 Information on uncultivated non

- agricultural areas, outdoor residential areas (paved

ar e as, driveways, patios, etc.), and aquatic sites (ponds, lakes, streams, etc.), including pounds a.i. applied, application timing, application rate, application method, and application frequency.Page 10 of 11

REFERENCES

Colquhoun, J., Mallory, C. S., and D. Ball. 2003. Weed Management in Clearfield Wheat with Imazamox. Oregon State Univ. Extension Service. Online. Available at: http://cropandsoil.oregonstate.edu/wheat/reports/ORCF_weed_mgt.pdf

. Accessed on , Jan. 27, 2013.

EPA Proprietary Data

, 1998

- 201 2

EPA

. Imazapyr Screening Level Usage Analysi s (SLUA), January 2013

Heap, I. The International Survey of Herbicide Resistant Weeds. Undated. Online. Available at: http://www.weedscience.org/summary/MOA.aspx . Accessed on, Jan. 17, 2014

University of Florida. 201 1 . Plant Management in Florida Waters: An Integrated Approach,

Ima zapyr Considerations. Available at: http://plants.ifas.ufl.edu/manage/developing

management

- plans/herbicide

- considerations/imazapyr

- considerations

- 0

Accessed on, Jan. 27, 2014.

University of Tennessee. (Undated) . Mode of Action Definitions. University of Tennessee,

Knoxvill e. Available at: http://hortweeds.tennessee.edu/webapp/test/moa.htm

. Accessed on
, Nov. 18, 2013.

USDA ERS. 2013. Adoption of Genetically Engineered Crops in the U.S.

Available at: http://www.ers.usda.gov/data

- products/adoption

- of

- genetically

- engineered

crops

- in

- the

- us/recent

- trends

- in

- ge

- adoption.asp x

. Online. Accessed on Feb. 6, 2014.

USEPA, 2006. Registration Eligibility Decision for Imazapyr. Online. Available at: http://www.epa.gov/oppsrrd1/REDs/imazapyr_red.pdf . Accessed on J an. 24 ,2014.

Wisconsin Department of Natural Resources. 2012. Imazapyr Chemical Fact Sheet. Online.

Available at: http://dnr.wi.gov/lakes/plants/factsheets/ImazapyrFactsheet.p df

. Accessed on Jan. 27, 2014.

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

Action . Weed Science Society of America. Online. Available at: http://wssa.net/wp

content/uploads/WSSA

- Mechanism

- of

- Action.pdf . Accessed on
, Jan.17 , 201 4

.

.Page 11 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 acre s 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 a

. i

. /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 particu lar 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 survey ed 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 Acr es 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.