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 ~ - L . 0 

BiOIO i alAnal ~ ~r/\l ~ 

Rafa rieto, Envft 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 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 Triasulfuron (128969), and eventually the general public. This document builds upon the data 

already provided in the "Usage and Label Use Data Packages" that are also provided to 
Registration Review teams by BEAD. The document is based on infonnation and data available 

to BEAD as of September 21, 2011. 

Triasulfuron is a selective herbicide used for the control of broad leaf and 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 of essential amino acids needed 

for plant growth. It can be applied as pre-plant, pre-plant shallow incorporated, or pre-or post 

emergence applications. To increase the weed control spectrum triasulfuron can be 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 of weeds 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 on private market pesticide usage data, triasulfuron's annual agricultural usage averaged 

30 thousand pounds of active ingredient (A. I. ) treating an average of 2 million acres from 1998-

2010. Since 1998, the use of tria sulfur on, both in pounds A.I. and acres treated, has varied. 

From 1998-2010, winter wheat accounted for the largest percentage of usage in tenns of total 

pounds of active ingredient applied (74%) and total area treated (72%). Spring wheat accounted 

for 13% of the pounds applied, and 15% of total area treated. 

The states with the most agricultural usage in terms of pounds 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, in tenns of pounds applied, for triasulfuron's largest agricultural 

markets. Overall, Figure 1 below shows that the total usage of triasulfuron has varied from 1998 

through 2010, with a spike in 2008 in use on winter wheat (Proprietary data, 1998-2010). 

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Figure 1. Pounds of Triasulfuron 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 of weed resistance, 

presence of 44 weed species resistant to ALS inhibitors have been reported in the United States 

(Heap et al. 2011). The highest usage of triasulfuron 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). Of these winter annuals, triasulfuron is effective on controlling 

downy brome (Bromus tectorum), horseweed'(Conyza canadensis), prickly lettuce (Lactuca 

serriola), field pennycress (Thlaspi arvense), tansy mustard (Descurainia pinnata), shepherd's 

purse (Capsella bursa-pastoris). and mustard species (Brassca spp.) (CDMS, 2011). 

mSTORY OF BEAD ASSESSMENTS FOR TRIASULFURON 

There were two assessments in the BEAD Official Records file that included triasulfuron. The 

first was a 2003 report in support of the reduced-risk registration decision for aminopyralid in 

which triasulfuron was considered as an alternative to control Canadian· thistle in pasture. 

Triasulfuron garnered less than 1 % of the 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 wheat in which triasulfuron is 

mentioned as an alternative in combination with dicamba in Kansas for control of hen bit. 

Dicamba plus triasulfuron was not a viable control alternative based on the relatively high cost of 

the chemical combination compared to other control alternatives. Because it was not presented 

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as a primary alternative, that suggests that triasulfuron had very low value as a control alternative 

for henbit in winter wheat 

A search of the 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 limited benefits for triasulfuron as an alternative control. 

DATA NEEDS RELEVANT TO BEAD'S FUTURE WORK ON TRIASULFURON 

There are no data needs at this 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 of Action. 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 

Bulletin No. 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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