UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON, D.C. 20460 

MEMORANDUM 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: BEAD Chemical Profile for Registration Review: Topramezone (123009) 

FROM: Colwell Cook, Entomologist ~ ~ Biological Analysis Branch 

THRU: 

Cynthia Doucoure, Environmental Protection Specialist 

Science Information and Analysis Branch 

Derek Berwald, Economist .Gr ( hlj \ d 1~, Economic Analysis Branch . J J V"~ 

Biological and Economic Analysis Division (75 

Amet Jones, Chief 

Biological Analysis Branch 

Diann Sims, Chief 

Science Information and Analysis Branch 

Timothy Kiely, Chief (I\_ \.M. ~. ) 

Economic Analysis Branch '-:J I~ 

Biological and Economic Analysis Division (7503P) 

TO: Jose Gayoso, Chemical Review Manager 

Risk Management and Implementation Branch II 

Pesticide Re-evaluation Division (7508P) 

Product Review Panel date: February 4, 2015 

Page 1 of9 
SUMMARY 

Topramezone, a pyrazolone herbicide, was first registered in the U.S. in 2005 for pre-emergence 

and postemergence control of broadleaf and grass weeds in field corn, popcorn, and sweet corn. 

More recent registrations include weed control in Christmas, conifer, and hardwood tree farms, 

field ornamental production, turf, and non-cropland areas. In addition, this chemical has been 

registered as an aquatic herbicide. Currently, topramezone is the only pyrazolone herbicide (a 

subclass of HPPD mechanism of action) in the U.S. The mechanism of action inhibits the 

Hydroxy Phenyl Pyruvate Dioxygenase (HPPD) enzyme which is required for carotenoid 

biosynthesis. Carotenoids are key in the removal of oxygen radicles which can destroy ceUs. 

Based on available private market research data, topramezone is reported to be used on field and 

sweet corn during the 2006-2013 time frames. Approximately 19,000 lbs a.i. were applied on 

average annually to 1.3 million acres of field and sweet corn at an overall average a.i. application 

rate ofO.Ol lbs a.i. per acre. Approximately 93% of the total pounds oftopramezone applied 

was to field corn but the percent crop treated (the ratio of base acres treated to crop acres grown) 

for field corn was <2.5%, whereas the percent crop treated for sweet corn was 15%. 

No national level topramezone usage data were found on nonagricultural sites. 

INTRODUCTION 

The purpose of this document is to convey usage information and a broad overview of the pest 

management roles of topramezone that is beginning to undergo registration review. The 

anticipated audience consists of the team of EPA staff currently evaluating the registration status 

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

provides in the Screening Level Usage Analysis (SLUA) to Registration Review teams. The 

document is based on information and data available to BEAD as of December 2014. 

HISTORY OF BEAD ASSESSMENTS FOR TOPRAMEZONE 

BEAD prepared a Screening Level Usage Analysis (SLUA) in December 2014 that provided 

average percent crop treated (PCT) values for field corn ( <2.5%) and sweet corn (I 5% ). The 

average annual pounds a.i. applied was 10,000 lbs a.i. to field corn and 1,000 lbs a.i. to sweet 

corn. These data are based on available public and private market research data. 

BEAD also reviewed submissions for a Public Interest Finding from the initial registration in 

2005. The review found that topramezone would have value to corn growers by increasing 

flexibility with a new mode of action. This would be useful as a resistance management tool, as 

well as reduced risk of crop-damaging interaction with some insecticides (Zinn, 2005). 

COMMON FORMULATIONS AND APPLICATION METHODS 

Topramezone is formulated as suspension (flowable) and emulsifiable concentrates. 

Page 2 of9 
USE SITES 

Agricultural Use Sites 

Topramezone is registered for use on field corn, popcorn and sweet corn, and during the fallow 

period. It is also used on nursery stock, sod turf farms, forest trees, and Christmas tree 

plantations. 

Non-Agricultural Use Sites: 

Topramezone is registered for use in aquatic areas, including ponds, lakes, reservoirs, marshes, 

wetlands, bayous, drainage ditches, canals and slow-moving or quiescent bodies of water. It is 

also used on ornamental lawns and turf, including recreational area and residential lawns. 

TOPRAMEZONE USAGE 

Agricultural Usage Trend 

Based on available private market research, topramezone is reported to be used predominantly on 

field and sweet corn in the U.S. During the 2006-2013 time frames, approximately 19,000 lbs 

a.i. were applied on average annually to 1.3 million acres of field and sweet corn at an overall 

average a.i. application rate ofO.Ol lbs a.i. per acre. Use oftopramezone on field corn, in terms 

of pounds a.i. applied, has increased since its registration in 2005, while use on sweet corn has 

remained relatively low as shown in Figure 1. Some of this reflects the relatively low acreage of 

sweet corn relative to field corn; as mentioned above, the SLUA indicates a greater percentage of 

sweet corn is treated with topramezone. Similar trends were found for the total area treated. 

Approximately 93% of the total pounds a.i. applied was reported to be used on field corn as 

shown in Table 1. However, the average a.i. application rates and labeled application rates were 

the same for both field and sweet corn. 

Page 3 of9 
Figure 1. Topramezone Pounds AI. Applied on Field and Sweet Com 2006-2013 

50,000 

0 

2006 2007 2008 2009 2010 2011 2012 . 2013 

Year 

..,._Corn ..,._Sweet Corn 

Source: Proprietary Data, 2006-2013 

Figure 2. Topramezone Total Area Treated (In Acres): Field and Sweet Com, 2006-2013 

3,000,000 

'0 

Q) 

-m 

Q) 

~ 

ro 

Q) 

~ 

ro 

0 

1-

0 

2006 2007 

Source: Proprietary Data, 2006-2013 

2008 2009 2010 2011 2012 2013 

Year 

..._Corn ..,._Sweet Corn 

Page 4 of9 
T bl e 1 T a opramezone T op C rops, 2006 -2013 

Percentage of Percentage of Labeled Max App Total Lbs 

A.l. of Total Area Avg A.I. Rate Rate per 

Topramezone Treated with (lb a.i./acre) Application 

Top Crops Applied Topramezone 

Field Corn 93% 94% 

Sweet Corn 7% 6% 

Sources: Propnetary Data, 2006-2013 

Topramezone LUIS Report, EPA, 2015 

Topramezone Top States, 2006-2013 

(lb a.i./acre) 

0.01 0.02 

0.01 0.02 

During the 2006-2013 time frame, topramezone is reported to be used in 18 states. However, in 

terms of the percent of total pounds a.i. applied, topramezone is used predominantly in the states 

oflowa (30%), Illinois (18%), and Indiana (14%) followed by Minnesota (10%) and Nebraska 

(9%) as shown in Table 2. Together, these states constitute over 80% of the total topramezone 

used during this period. 

T a bl e 2 T opramezone T op S tates, 2006 -2013 

State Share of State Share of 

Total Lbs A.I. of Total Area 

Topramezone Treated with A vg A. I. Rate 

Top States Applied Topramezone (lb a.i./acre) 

Iowa 28% 31% 0.01 

Illinois 18% 17% 0.02 

Indiana 15% 13% 0.02 

Nebraska 12% 11% 0.01 

Other 27% 28% 0.01-0.02 

*Other states include CO, ID, KS, KY, MN, MO, ND, OH, OR, PA, SD, TX, WA, and WI. 

Source: Proprietary Data, 2006-2013 

Agricultural Use Intensity of Topramezone Use 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 1,000 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 topramezone's higher use intensity in the U.S. in 

Iowa and Indiana, which is driven by production of field corn and in Illinois, Minnesota, and 

Nebraska, which is driven by production of field and sweet corn. The higher use intensity in 

South Carolina and Washington results from low crop acres grown within the states. For more 

information on Figure 3, see Appendix A. 

Page 5 of9 
Figure 3. Annual Average Agricultural Use Intensity of Topramezone (2009-2013). 

Pounds Active Ingredient 

per 1,000 Crop Acres Grown 

0No0ata 

< 0.015 

0 01 5 -0025 

- 0 025 - 0.095 

- 0.095 - 0.25 

- > 0.25 

(Source: Proprietary Data, 2009-2013) 

Non-agricultural Usage 

The available public and private databases on nonagricultural uses did not report national level 

usage of topramezone. 

Page 6 of9 
BIOLOGICAL ASPECTS RELEVANT TO TOPRAMEZONE 

Topramezone provides preemergence and postemergence weed control (Shaner, 2010). 

Topramezone is in the group of herbicides known as pyrazolones and is in Group 27 of the Weed 

Science Society. These herbicides have the mechanism of action of inhibiting the HPPD 

enzyme, which is required for carotenoid biosynthesis. Carotenoids are key in the removal of 

oxygen radicles which can destroy cells. 

The primary use of topramezone is in field com where it is used to control broadleaf weeds such 

as common waterhemp, lambsquarters and some pigweeds, as well as grass weeds such as the 

various types of foxtails. In sweet com this herbicide is used to control many of the same 

broadleaf and grass weeds as well as broadleaf weeds such as redroot pigweed and grasses such 

as wild proso millet. In November of 2013, topramezone was federally registered as an aquatic 

herbicide. Other registrations in 2014 allow for topramezone postemergence weed control in 

Christmas, conifer, and hardwood tree farms, field ornamental production, turf, and non-cropland 

areas. 

ROLE OF TOPRAMEZONE IN PEST MANAGEMENT 

Currently topramezone is the only pyrazolone herbicide in the U.S., a type of HPPD inhibitor. 

This new mode of action is useful for rotation with other herbicides with different modes of 

action for managing weeds, such as pigweeds, lambsquarters, and foxtails, especially in sweet 

com and popcorn, which have fewer herbicide options (Zinn, 2005). Growers of sweet com are 

concerned with resistance to triazine and ALS inhibitors; in addition certain sweet corn varieties 

are sensitive to some herbicides (Zinn, 2005). Topramezone plays a role in weed management in 

these crops because of its unique mode of action. Topramezone is the only HPPD herbicide 

registered for aquatic weed control and can be used as part of a resistance management program 

(Aquatic Plant Management Society, Inc., 2-14). 

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

TOPRAMEZONE 

The Agency currently does not have complete information on topramezone. Obtaining the 

following usage information may improve future assessments conducted by the Agency related 

to the use and importance of topramezone: 

• Aquatic areas: usage data (pounds a.i. applied per year, maximum rate of application, 

number of applications per year) 

• Agricultural and nonagricultural uses including nursery stock, Christmas and forest 

tree plantings, ornamental lawns and turf: usage data (pounds a.i. applied per year, 

maximum rate of application, number of applications per year) 

Page 7 of9 
REFERENCES 

Aquatic Plant Management Society, Inc. 2014. Herbicide resistance stewardship in aquatic 

plant management. Available at: http:/ /apms.org/wp/wp-content/uploads/20 14/04/HerbicideResistance-Stewardship-in-Aguatic-Plant-Management.pdf. Accessed: February 4, 2015. 

EPA, Topramezone Screening Level Usage Analysis (SLUA), August 2014 

Proprietary Data, 2006-2013 

Shaner, DL. 2014. Herbicide Handbook Tenth Edition. Weed Sci. Soc. of Am. 810 E. lOth 

Street, Lawrence, KS 66044-8897. U.S.A. 

Zinn, Nicole. Evaluation of Public Interest Documentation for the Conditional Registration of 

T'opramezone on Field Com, Sweet Com, and Pop Com, D313195. US EPA, May 13,2005. 

Page 8 of9 
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 ail 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 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 (I ,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 9 of9