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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON, D.C. 20460

DEC 0 6 2013

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION

MEMORANDUM

SUBJECT: 

FROM:

THRU:

TO:

BEAD Chemical Profile for Registration Review: Dithiopyr (128994) 

Sunil Ratnayake, Biologist /\ Jr""\

Biological Analysis Branch (_ \

Cynthia Doucoure, Environmental Protection Specialist {j _ -

Science Information and Analysis Branch

Stephen Smearman,Economist

Economic Analysis Branch

Biological and Economic Analysis Division (7503P)

Arnet Jones, Chief /J ...+.. 'i

Biological Analysis Branch Ylf

Diann Sims, Chief 4.· "

Science Information and Analysis Branch

Timothy Kiely, Chief L 

Economic Analysis Branch \J ) \

Biological and Economic Analysis Division ( 3P)

V. Dutch, Chemical Review Manager

Risk Management and Implementation Branch 4

Pesticide Re-evaluation Division (7508P)

Product Review Panel date: July 17, 2013
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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 dithiopyr, and eventually the general public. This document builds upon the data already 

provided in the Label Use Information System (LUIS) reports and the Screening Level Usage 

Analysis (SLUA) that BEAD provides to the Registration Review teams. The document is based 

on information and data available to BEAD as ofNovember 2013.

Dithiopyr was first registered in the U.S. in 1991 as a conventional herbicide (USEPA, 1991). 

Dithiopyr herbicide belongs to the pyridines group of herbicides (Weedscience.org, 2013). It is 

applied as a pre and post-emergence herbicidefor the control of grasses and small seeded broad 

leaf weeds. This herbicide is not registered for agricultural uses and it is predominantly used for 

the control of grass weed species in non-agricultural sites described below. According to the 

Weed Science Society of America (WSSA) mechanism of action classification, dithiopyr

belongs to the group 3 herbicides. The mechanism of action of this group of herbicides is 

inhibition of assembly of microtubules in the process of cell division of susceptible weeds 

(Weedscience.org, 2013).

HISTORY OF BEAD ASSESSMENTS FOR DITHIOPYR

A search of the BEAD Official Records data base did not find any relevant assessments for 

dithiopyr.

COMMON FORM ULATIONS AND APPLICATION METHODS

Dithiopyr is formulated as emulsifiable,suspension, and soluble concentrates, water soluble 

pouches, granules, and liquids ready-to-use. Dithiopyr is applied as a ground broadcast 

application using rotary- or drop-type spreaders, conventional liquid application equipment 

including hand-operated sprayers (backpack, tank or pump-up type), and hose-end sprayers. 

Dithiopyr is also used as a crack and crevice treatment using a foam applicator.

USE SITES

Agricultural Use Sites

Dithiopyr is not registered for use on agricultural crops. 

Non-Agricultural Use Sites

Dithiopyr is labeled for use on landscape,field, and container grown ornamentals located in 

ornamental gardens, parks, golf courses, and residential areas; on nonbearing fruit and nut trees 

(nonfood producing trees); on turf sites (residential and institutional lawns, athletic fields,
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commercial sod farms, and golf course fairways, and roughs); and uncultivated nonagricultural 

areas including roadsides, utility right-of-ways, railways, and industrial areas.

PROFESSIONALTURF AND ORNAMENTAL USAGE IN THE U.S.

Dithiopyr is used primarily in the professional turf and ornamental markets as a pre-emergence 

herbicide in the U.S., as reported in private market research studies for the years 2004, 2006, and

2011. When it comes to dithiopyr sales by brand, Dimension®, is one of the top herbicides used 

on golf courses and by lawn care operators and is gaining ground in other sectors. Total use of 

Dithiopyr in terms of pounds a.i. applied, has reportedly increased by nearly 200% since 2004 as 

shown in Table 1. Acre treatments of the brand, Dimension®, have also increased by 17% since

2004. The predominant use in the professional turf and ornamental market is on golf courses and 

lawns. However, the most recent years of data show use increasing in terms of pounds ai applied 

and in acre treatments for areas such as horticultural nurseries, institutional turf, and landscape 

contractors as shown in Tables 1 & 2.

Table 1. Dithiopyr Pounds A.I. Applied, 2004, 2006, and 2011

Sector

Pounds A.l. Applied: Pre-emergence

(Thousand Lb A.l.)

2004 2006 201l

Golf Courses 48 66 95

Lawn Care Operators (LCOs) 102 97 223

Horticultural Nurseries N/A N/A 42

Institutional Turf N/A NIA 46

Landscape Contractors N/A 15 38

Turf Farms N/A NIA 5

Total 150 178 449

Source: EPA Propnetary Data, USA, 2005,2007, and 2012

Table 2. Product (Dimension®) Acre Treatments, 2004, 2006, and 2011

Sector

Product (Dimension®)Acre Treatments:

Pre-emergence

Thousand Acres)

2004 2006 2011

Golf Courses 222 198 168

Lawn Care Operators (LCOs) 502 382 369

Horticultural Nurseries N/A N/A 118

Institutional Turf NIA 56 102

Landscape Contractors NIA 55 80

Turf Farms 7 24 19

Total 731 715 856

Source: EPA Proprietary, 2005, 2007, and 2012
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BEAD also found one year of data in USDA NASS (2009) for dithiopyr, which shows that 100 

pounds of dithiopyr were applied on nursery and floriculture at an average application rate of

0.472 lb/acre. This application rate is only slightly lower than the dithiopyr maximum single 

application rate of 0.498 lb/acre on ornamental lawns, turf, and landscape ornamentals as found 

on dithiopyr labels.

BIOLOGICAL ASPECTS RELEVANT TO DITIDOPYR

Dithiopyr is an herbicide applied for the control of annual grasses and broadleaf weeds in nonagricultural sites. Dithiopyr is effective on controlling major grass weed species such as barley 

(Hordeum spp.) large crabgrass (Digitaria sanguinalis),smooth crabgrass (Digitaria ischaemum), 

southern crabgrass (Digitaria ciliaris), barnyardgrass (Echinochloa crus-galli), goosegrass 

(Elusine indica), and foxtails (Setaria spp.) (Dimension® EC. Product Label. 2003). In addition, 

dithiopyr is used to control annual broadleaf species such as carpet weed (Mollugo verticillata), 

Chickweed (Stellaria spp.) henbit (Lamium spp.) prostrate knotweed (Polygonum aviculare), 

redroot pigweed (Amaranthus retrojlexus), and spurge (Euphorbia) species.

According to the Weed Science Society of America (WSSA) mechanism of action classification, 

dithiopyr belongs to the group 3 herbicides and presence of biotypes of 6 weed species

resistant to group 3 herbicides has been reported in the United States (Weedscience.org, 2013). 

These weed species are Palmer amaranth (Amaranthus palmeri), wild oats (Avenafatua), 

goosegrass (Eleusine indica), rigid ryegrass (Lolium rigidum), annual bluegrass (Poa annua), 

green foxtail (Setaria viridis), and Johnsongrass (Sorghum halepense). Although the presence of 

biotypes of weeds with resistance to dithiopyr is reported, a reduction of usage is not observed. 

This may be due to the effectiveness of this herbicide on controlling major grass weeds found in 

many non-agricultural sites.

Among the major grass weeds, dithiopyr controls several crabgrass species (large crabgrass, 

smooth crabgrass, southern crabgrass). Pre-emergence as well as post-emergence applications of 

dithiopyr are recommended and a better crabgrass control can be achieved by post-emergence 

applications of this herbicide during the early growth stage of crabgrass (before tillering). Postemergence applications at early growth stages can provide 2 to 8 weeks of additional control of 

crabgrass found in the fields. According to the product label, applications of dithiopyr can be 

made as a single application or sequential application in the spring, summer, or fall. However, not

more than 1.5 lb ai/ac should be applied per year using split or sequential applications 

(Dimension® EC, Product label, 2003).

ROLE OF DITIDOPYR IN PEST MANAGEMENT

Dithiopyr is used primarily for preemergence control of annual grasses and broadleaf weeds in 

established lawns, golf courses, ornamental turf, commercial sod farms, non-croplands, industrial 

sites, field grown or container grown nursery ornamentals. The predominant use of dithiopyr in
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the professional turf and ornamental market is on golf courses and lawns. However, the most 

recent years of data show use increasing in terms of pounds ai applied and in acre treatments for 

areas such as horticultural nurseries, institutional turf, and landscape contractors. Based on the 

available data, it appears that use of dithiopyr on these sites has been increasing overall from

2004 to 2011, which is an indication of the relative importance of dithiopyr to the professional 

turf and ornamental market in controlling weeds. The role of dithiopyr in pest management in 

uncultivated non-agricultural sites, however, is not apparent due to the lack of available data.

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

DITHIOPYR

Obtaining additional information on the current use of dithiopyr in uncultivated non-agricultural 

and industrial sites would improve future BEAD assessments and may be required as part of the 

registration review of this pesticide. Information needed regarding the current use of dithiopyr on 

all sites includes the annual pounds of a.i. applied in the U.S., the number of acre treatments, 

typical application rates (single and yearly), and the number of applications per year.

REFERENCES

Dimension® EC. Product Label. 2003. Dow AgroSciences LLC. Indianapolis, fN46268, USA. 

http:/lpdf.tinnsdev.com/Web/35/6945/35 6945 LABEL English .pdr?download=true

Date Accessed. July 3, 2013.

Dithiopyr. Weedscience.org. 2013. http://www.wecdscience.org/summary/I lerbicide.aspx. Date

Accessed. June 6, 2013.

International Survey of Herbicide Resistant Weeds. 2013. 

ohttp://www.weedscience.org/summary/MOA.aspx . Date Accessed,June 17, 2013.

Kline &Company. 2005,2007, and 2012

Pesticide Fact Sheet Number 223. 1991. USEPA.

http://massmc.org/ipm/docs/EPA Factsheet Dithiopyr.pdf. Date Accessed. June 6, 2013. 

USDA NASS. 2009 Nursery and Floriculture Chemical Use.