UNITED STATES ENVIRONMENTAL PROTECTION AGENCY WASHINGTON, D.C

. 20460 

### OCT 25 

### 2011

MEMORANDUM OFFICE OF CHEMICAL SAFETY AND POLLUTION PREVENTION

SUBJECT: BEAD Chemical Profile for Registration Review: Triasulfuron (128969) 

### FROM: Sunil Ratnayake, Biologist

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## L

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# BiOIO**i** alAnal

# ~**~r/\l ~**  Rafa rieto, Envf t nmental Protection Specialist Science ormation and

### AnalYSiS**Branch .** **'AA~** Stephen Smearman, Economist

### ~­ Economic Analysis Branch Biological and Economic Analysis Division (7503P) THRU: Arnet Jones, Chief Biological Analysis Bran Diann Sims, Chief 

# )f1 Science Information and Analysis Branch Timothy Kiely, Chief 

# .QJ**I~** Economic Analysis Branch 

# M**~** Biological and Economic An ysi Division (7 P) TO: Andrea Mojica, Chemical Review Manager Risk Management and Implementation Branch 4 Pesticide Re-evaluation Division (7508P)
Product Review Panel date: September, 21, 2011 INTRODUCTION The purpose ofthis document is to convey usage information and a broad overview ofthe pest management roles ofpesticides that are beginning to undergo registration review. The anticipated audience consists ofthe team ofEPA staffcurrently evaluating the registration status ofTriasulfuron (128969), and eventually the general public. This document builds upon the data already provided in the "Usage and Label Use DataPackages" that are also provided toRegistration Review teams by BEAD. The document is based on infonnation and data available to BEAD as ofSeptember 21, 2011. Triasulfuron is a selective herbicide used for the control ofbroadleafand grassy weeds in wheat, including: durum wheat, barley, fallow cropland, pastures, rangeland, and lands considered as conservation reserves. Triasulfuron herbicide controls weeds by inhibiting the enzyme acetolactate synthase (ALS) which is important for the synthesis ofessential amino acids needed for plant growth. Itcanbe applied as pre-plant, pre-plant shallow incorporated, or pre-or post emergence applications. To increase the weed control spectrum triasulfuron canbe tank mixed with other compatible herbicides. USE SITES Agricultural Use Sites Triasulfuron is used on winter wheat, spring wheat, barley, fallow, rangeland, and pastureland. Also, this chemical is used for post-harvest control ofweeds in cereal crops and small grains. Non-Agricultural Use Sites Triasulfuron is not registered for non-agricultural use. COMMON FORMULATIONS AND APPLICATION METHODS Triasulfuron is only fonnulated as water dispersible granules. Triasulfuron can be applied using ground or aerial spray equipment.
. USAGE Based onprivate market pesticide usage data, triasulfuron's annual agricultural usage averaged 30 thousand pounds ofactive ingredient (A.I.) treating an average of2 million acres from 1998- 2010. Since 1998, the use oftriasulfur on, both in pounds A.I. and acres treated, has varied. From 1998-2010, winter wheat accounted for the largest percentage ofusage in tenns oftotal pounds ofactive ingredient applied (74%) and total area treated (72%). Spring wheat accounted for 13% ofthe pounds applied, and 15% oftotal area treated. The states with the most agricultural usage interms ofpounds A. I. applied are: Kansas (34%), Texas (16%), Montana (16%), and Nebraska (13%). The states with the most total area treated were: Kansas (31 %), Montana (20%), Texas (14%), and Nebraska (14%). (Proprietary data, 1998-2010) USE TRENDS Figure 1 depicts usage trends, intenns ofpounds applied, for triasulfuron's largest agricultural markets. Overall, Figure 1 below shows that the total usage oftriasulfuron has varied from 1998 through 2010, with a spike in 2008 in use on winter wheat (Proprietary data, 1998-2010).

2Figure 1. Pounds ofTriasulfuron Applied (1998-2010) to Agricultural Sites. 50,000 

## Triasulfuron Usage Trend

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 Year • Wheat, Spring

. Wheat, Winter U All Other Crops
Note: "All Other Crops" refers to Barley, Fallow, and PasturelRange. Source: Proprietary data, 1998-2010. BIOLOGICAL ASPECTS RELEVANT TO TRIASULFURON Triasulfuron belongs to the sulfonylurea herbicide family which inhibits the activity of acetolactate synthase enzyme (ALS). According to a survey on development ofweed resistance, presence of44 weed species resistant to ALS inhibitors have been reported inthe United States (Heap et al. 2011). The highest usage oftriasulfuron is on winter wheat (Fig. 1). The major weeds in winter wheat are winter annuals or other weeds with a life cycle similar to winter wheat (peel and Riveland, 1997). Ofthese winter annuals, triasulfuron is effective on controlling downy brome (Bromus tectorum), horseweed'(Conyza canadensis), prickly lettuce (Lactuca serriola), field pennycress (Thlaspi arvense), tansy mustard (Descurainiapinnata), shepherd's purse (Capsella bursa-pastoris). and mustard species (Brassca spp.) (CDMS, 2011). mSTORY OF BEAD ASSESSMENTS FORTRIASULFURON There were two assessments in the BEAD Official Records file that included triasulfuron. The first was a 2003 report in support ofthe reduced-riskregistration decision for aminopyralid in whichtriasulfuron was considered as an alternative to control Canadian·thistle inpasture. Triasulfuron garnered less than 1

### % ofthe market share meaning that it was not considered an important control alternative. The second document was a 2005 addendum to the chlorsulfuron benefits discussion for aerial applications alternatives in winter wheatin which triasulfuron is mentioned as an alternative in combination with dicamba in Kansas for control ofhen bit. Dicambaplus triasulfuron was not a viable control alternative based onthe relatively high cost of the chemical combination compared to other control alternatives. Because it was not presented 3as a primary alternative, that suggests that triasulfuron had very low value as a control alternative for henbit in winter wheat A search ofthe BEAD Section 18 data base yielded no results for triasulfuron in Section 18 requests for any crop. This again suggests that triasulfuron would not be used as an alternative for weed control for the pests presented above and it would be expected that there would be very limitedbenefits for triasulfuron as an alternative control. DATA NEEDS RELEVANT TO BEAD'S FUTURE WORK ON TRIASULFURON There are no data needs atthis time. REFERENCES CDMS. 2011. Amber® Herbicide Product Label. Syngenta Crop Protection Inc. Greensboro, North Carolina. NC 27419-8300. http://www.cdms.netiLDat/ld48P020.pdf
. Accessed on Sep. 21,2011. Heap, I, H
. Glick, L Glasglow, and W
. Vencill. 2011. Herbicide Resistant Weeds by Country and Site ofAction
. 2011. http://www.weedscience.org/summary/countrysummary.asp
. Accessed on Sep. 12, 2011. Peel, M. D. and N. Riveland. 1997. Winter wheat production in North Dakota. 1997. Extension BulletinNo. 33. North Dakota State University. http://www.ag.ndsu.edu/pubs/plantsci/smgrains/eb33w.htm#weed
. Accessed on Sep. 21, 2011. Proprietary data, 1998-2010.

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