UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON. D.C. 20460 

JAN 26 lm5 

OFFICE OF CHEMICAL SAFETY 

ANn Pnl I IITinN PI'II=\/I=NTinN 

MEMORANDUM 

SUBJECT: 

FROM: 

THRU: 

TO: 

BEAD Chemical Profile (BCP) for Registration Review: Thidiazuron (120301) 

Sunil Ratnayake, Biologist ~ . \-- 1 _ Biological Analysis Branch ~ ··~ ~g.., ~ 

Cyntnia 

Science Information 

Doucoure, Environmental 

and Analysis Branch 

Protection Specialist {!,, ~ 

Stephen Smearman, Economist~~ Economic Analysis Branch 

Biological and Economic Analysis Division (7503P) 

Arnet Jones, Chlef 

Biological Analysis Branch 

Diann 

Science 

Sims, 

Information 

Chief 

and 

~ Anutalysis Branch~~ 

Timothy Kiely, Chief 

Economic Analysis Branch ~ Biological and Economic Analysis Division 3P) 

Khue Nguyen, Chemical Review Manager 

Risk Management and Implementation Branch IV 

Pesticide Re-evaluation Division (7508P) 

Product Review Panel date: November 26,2014 

Page 1 of8 
SUMMARY 

Thidiazuron was first registered in the U.S. in 1982. This pesticide is used as a pre-harvest 

treatment (treatment applied before harvesting) on cotton as a defoliant to reduce the foliage and 

immature fruiting structures which contribute to the staining of harvested cotton. Applications of 

thiadiazuron also facilitates cotton harvesting and reduces the pieces of dry leaves and other inert 

matter in harvested cotton. 

During the 2008-2012 time frame, an average of approximately 250,000 pounds a.i. of 

thidiazuron were applied annually to 3.8 million acres at an overall average application rate of 

0.07 lb a.i. per acre. The top states, in terms of the percentage of the total pounds a.i. applied, 

were Georgia, Texas, Mississippi, and Arkansas. The average percent crop treated (PCT) for use 

ofthidiazuron on cotton during 2004-2012 was 30 percent. According to 2008 to 2012 usage 

data, the highest usage ofthidiazuron was observed in Georgia and Texas. These two states 

account for 46 percent of the cotton acreage treated with thidiazuron. 

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 thidiazuron, and eventually the general public. This document builds upon the data BEAD 

provides in the Label 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 September 2014. 

HISTORY OF BEAD ASSESSMENTS FOR PROPOXYCARBAZONE SODIUM 

BEAD prepared a Screening Level Usage Analysis (SLUA) for thidiazuron in September 2014 

based on available data from 2004 to 2012 which shows that the average percent crop treated for 

cotton was approximately 30 percent and the average annual pounds a.i. applied was 300,000. 

A search of BEAD's Official Records data base for BEAD benefits assessments specifically for · 

thidiazuron did not find any records of prior BEAD assessments specifically for this chemical in 

the last 10 years. 

Emergency Exemptions- A search of BEAD's Official Records did not find any Section 18s 

requests for thidiazuron in the last 1 0 years. Emergency exemptions may indicate that there is a 

need for a particular chemical that is not registered for· use on a particular site. An emergency 

exemption request may yield information about a particular chemical's importance or value that 

is not found in other EPA records. However, a lack of Section 18 assessments by BEAD does 

not specifically indicate the relative importance of the chemical. 

Page 2 of8 
COMMON FORMULATIONS AND APPLICATION METHODS 

Thidiazuron is formulated as wettable powder in water soluble bags, or as suspension and 

emulsifiable concentrates and applied as a pre-harvest application via ground or aerial 

application equipment. This product is not to be applied using any type of irrigation system. 

USE SITES 

Agricultural Use Sites: 

Thidiazuron is registered for use as a cotton defoliant. 

Non-Agricultural Use Sites: 

There are no non-agricultural use sites registered for thidiazuron 

THIDIAZURON USAGE 

Agricultural Usage Trend 

Based on the available proprietary data for the time period from 1998 through 2012, thidiazuron 

use on cotton in the U.S. fluctuated with a significant decrease in 2008 followed by a significant 

increase in use for the remainder of the time period through 2012 as shown in Figure 1. The long 

term use trend has remained positive, gradually increasing over the period from 1998 through 

2012. Similar patterns were seen for the total area treated with thidiazuron as shown in Figure 2. 

During this period, an average of approximately 255,000 pounds a.i. were applied annually to 4.2 

million acres at an overall average application rate of 0.06 lb a.i. per acre. 

In recent years (2008-2012), use ofthidiazuron on cotton in terms of both total pounds and acres 

treated has recovered to pre-2007 levels as seen in Figure 1 and Figure 2. For this time period, 

an average of approximately 250,000 pounds a.i. were applied annually to 3.8 million acres at an 

overall average application rate of0.07 lb a.i. per acre. The top states, in terms of both the 

percentage of the total pounds a.i. applied and acre treatments are Georgia, Texas, Mississippi, 

and Arkansas as shown in Table 1. The maximum labeled application rate for thidiazuron use on 

cotton is 0.2 lb a.i. per application and 0.3 lb a.i. per year. 

Page 3 of8 
Figure 1. Thidiazuron Usage on Cotton: Pounds AI Applied, 1998-2012 

400,000 

0 

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

Year 

Source: Proprietary Data, 1998-2012 

Figure 2: Thidiazuron Usage on Cotton: Total Area Treated, 1998-2012 

6,000,000 

0 

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

Year 

Source: Proprietary Data, 1998-2012 

Page 4 of8 
T a e bl 1 T S op tates fi or U se o fThid. tazuron on c otton, 2008 -2012 

Top States Percentage of Percentage of A vg A. I. Rate 

Total Pounds A.I. Total Area (lb a. i./acre) 

Applied Treated 

Georgia 22% 23% 0.06 

Texas 23% 23% 0.06 

Mississippi 12% 11% 0.07 

Arkansas 8% 8% 0.06 

*Other 35% 35% 0.07 

*Other states include AL, AZ, CA, FL, KS, LA, MO, NC, OK, SC, and TN. 

Agricultural Use Intensity ofThidiazuron Use on Cotton in the U.S. 

Another measure of usage is the use intensity. In this analysis, the use intensity is expressed as 

the average annual amount (in pounds) of the active ingredient applied per I ,000 acres of crop 

acres grown. This differs from the application rate, which is expressed as the pounds a.i. applied 

per treated area. Figure 3 spatially represents thidiazuron's use intensity in the U.S. in Georgia, 

Texas, Mississippi and Arkansas. For more information on Figure 3, see Appendix A. 

Page 5 of8 
Figure 3: Annual Average Agricultural Use Intensity of Thidiazuron 2008*2012 

Pounds Active Ingredient 

per 1,000 Crop Acres Grown 

0 No0ata 

c:J <1 

0 1-2 

- 2-5 - 5 - 10 

- >10 

Source: Proprietary Data, 2008*2012 

USE OF THIDIAZURON IN COTTON PRODUCTION 

Thidiazuron is a hormonal type cotton defoliant applied as a pre-harvest treatment to reduce the 

plant foliage to facilitate harvesting. Also, this chemical reduces the amount of trash in harvested 

cotton and improves the lint grade. Generally cotton d~foliants are applied in the field when 60 

percent of the cotton bolls in a plant are open (Dodds et al., 2014). Chemicals used as defoliants 

can injure the cotton plant and cause it to produce ethylene. Ethylene production promotes 

formation of an abscission layer and separation of the leaf from the plant resulting the leaf drop 

(Dodds et al., 2014). 

Tribufos, carfentrazone, pyraflufen-ethyl, glyphosate, and paraquat are some of the chemicals 

that can be used as alternatives to thidiazuron. Tank mixing thidiazuron with tribufos, as well as 

the addition of silicone surfactants or ammonium sulfate have been shown to increase uptake of 

thidiazuron in drought stressed cotton. Also, compared to some other defoliants, thidiazuron has 

shown an excellent ability to prevent regrowth which makes it easy for harvesting. (Dodds et al., 

2014). 

Page 6 of8 
REFERENCES 

Arysta LifeSciences. North America, LLC. Undated. Thiadiazuron 4 SC. Product Label. 15401 

Weston Parkway, Suite 150. Carry, NC27513. Online Publication. Available at: 

http://www.agrian.com/pdfs/Thidiazuron 4 SC Labell.pdf. Accessed on Nov. 14, 

2014. 

Dodds, D. M., Reynolds, D. B., Barber, L.T., and T. B. Raper. 2014. Mid-South Cotton 

Defoliation Guide: Online Publication. Available at: http://www.mississippicrops.com/wp-content/uploads/20 14/09/20 14-Cotton-Defoliation-Guide Final.pdf 

Accessed on Dec.23, 2014. 

EPA, Thidiazuron Screening Level Usage Analysis (SLUA), September 2014. 

Proprietary Data, 1998-2012. 

USEP A. 2005. Registration Eligibility Decision of Thiadiazuron. Online Publication. Available 

at: http://www.epa.gov/oppsrrd1/REDs/thidiazuron red.pdf. Accessed on Nov. 17,2014. 

Page 7 of8 
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 acres 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. 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 m,ajority of the crop. Although 

the surveys capture most of the use of a particular 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 surveyed 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 Acres 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. 

Page 8 of8