UNITED STATES ENVIRONMENTAL PROTECTION 

AGENCY 

WASHINGTON, D.C. 20460 

SEP 16 2014 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

MEMORANDUM 

SUBJECT: 

FROM: 

Information to support registration review of dicrotophos: cotton crop phenology 

in the southern U.S., recent dicrotophos use patterns, and potential alternative 

insecticides 

Nikhil 

Jonathan 

Mallampalli, 

Becker, Ph.D., 

Ph.D., 

Senior 

Entomologist 

Science Advisor ML~· ,~--­ ~)' _,drvBiological Analysis Branch 

Donald 

Science 

Atwood, 

Information 

Ph.D., 

and 

Entomologist 

Analysis Branch 

.Jf~J! /Jt/. ~ 

Biological and Economic Analysis Division (7503P) 

TH,ROUGH: Amet Jones, Chief 

Biological Analysis Branch 

Diann Sims, Chief 

Science Information and Analysis Branch 

Biological and Economic Analysis Division (7503P) 

TO: Andrew Shelby, Environmental Scientist 

Nathan Miller, Environmental Scientist 

Mark Corbin, Chief 

Environmental Risk Branch 6 

Environmental Fate and Effects Division (7507P) 

Thurston G. Morton, Chemist, 

Elissa Reaves, Chief 

Risk Assessment Branch 4 

Health Effects Division (7509P) 

Russell Wasem, Chemical Review Manager 

Neil Anderson, Chief 

Risk Management and Implementation Branch 1 

Pesticide Reevaluation Division (7508P) 

Page 1 of9 
BEAD Peer Review Panel date: August 27,2014 

SUMMARY 

In this document, the Biological and Economic Analysis Division (BEAD) provides information 

on cotton phenology, cropping dates, dicrotophos application timing, and potential alternatives, 

for selected regions of the United States. BEAD recommends that this information should be 

used as input parameters when refining the modeling of surface water concentrations. BEAD 

also provides information related to the available alternatives for agronomically important pests 

treated with dicrotophos. 

INTRODUCTION 

Dicrotophos (Bidrin®) is currently the subject of risk assessment as part of the registration 

review process. The only agricultural use currently registered is cotton. Dicrotophos is a broad 

spectrum, partially systemic organophosphate insecticide that underwent reregistration review in 

2002, and the reregistration eligibility decision was made final in 2006. After that review, only 

two uses remain registered: cotton and landscape tree injection. While dicrotophos was once 

widely used in cotton and other non-food crops (it was first registered in 1964), use in cotton 

declined by the early 2000s. One factor may have been that several insects once targeted with 

dicrotophos use, such as the cotton aphid and silverleaf whitefly, showed resistance to the 

material (Atwood 2012). Other factors probably contributing to a decrease in use of dicrotophos 

in more recent years include the widespread adoption of genetically modified Bt cotton (which 

effectively controls caterpillar pests), and the ramping down and eventual elimination of the boll 

weevil eradication program in all states except Texas, which historically required prophylactic 

treatments with many different insecticides for season-long control (Stevenson and Matocha 

2005, USDA 2009, APHIS 2013). 

However, since at least 2008, proprietary survey data indicate a slight increase in dicrotophos use 

nationally, with a proportionally greater increase in use (in terms of acres treated and pounds of 

dicrotophos use) in southeastern states such as Georgia, North Carolina, and Louisiana. The 

major targets ofthis use appear to be a complex of stinkbug species, including the green stinkbug 

(Acrosternum hi/are), the brown stinkbug (Euschistus servus), and the southern green stinkbug 

(Nezara viridula). All had historically been relatively minor pests until Bt cotton became 

widespread (Stevenson and Matocha 2005, Herbert et al. 2009). Use of dicrotophos against the 

tarnished plant bug also continues at a comparatively high rate (in terms of acres treated per 

year), but has declined compared to the 1990s, probably because ofthe spread ofresistant 

insects. 

COTTON PHENOLOGY 

Cotton (Gossypium spp.) is a perennial warm-season crop that requires a long growing period 

(USDA 2009). However, it is grown as an annual crop, with fields being mowed down and 

replanted each year. Figure 1 below summarizes typical development of cotton, with a focus on 

square and boll development, for cotton grown in the southern United States. A "square" is the 

Page 2 of9 
developing cotton flower which, after pollination, will give rise to the boll (the harvested part of 

the plant). 

C:::::ll EARL'Y 5EASDH1 t:::==::J ~I) SEASON Cl =· ===:::::JII.lA'r'E '5£~ IC:: . =:::1 

400,- ILl' ~ 

200~ It 

E ... wri!l 

• 

0 :ZD 

I I 

W«, JIJHf , 

40 flO 80 JOO 

I 

.iiULY 1 

Days After Plantlna 

Bolt! .and F'lbl:•r 

.w.aturllltfaon 

JL 

120 140 

I 

160 

CCT 1 

Figure 1. Development of cotton in the Mid-South with a May 1 planting date, showing typical 

production patterns of squares, bolls and open bolls (NCCA 20 14). 

Based on the most recent planting and harvest dates (USDA 2010) and on cotton phenology from 

the National Cotton Council (2014), Table 1 below describes crop development data that should 

be used for refinements to the drinking water risk models, for specific regional scenarios. 

Table 1. Plantin~ and harvesting date for cotton in three states based on USDA (20 1 0). 

I·· 

State Planting1 Emergencel Maturation3 Harvest' 

Mississippi 10-May 20-May 9-Jul 10-0ct 

North Carolina 10-May 20-May 9-Jul 1-Nov 

Texas 7-May 17-May 6-Jul 30-0ct 

Notes: 

1. Planting date is the midpoint of the most active planting date range for each state from USDA (2010). 

2. Emergence date is calculated by adding 10 days to the planting date. 

3. Maturation date calculated by adding 60 days to the planting date. The term "maturation date" is used to 

refer to the date when the vegetative portion of the plant has developed to intercept the maximum amount 

of precipitation. This is considered to be equivalent to canopy closure. 

4. Harvest date is the midpoint of the most active harvesting date range for each state from USDA (2010). 

Page 3 of9 
DICROTOPHOS USAGE RELEVANT TO THE RISK ASSESSMENT 

BEAD examined recent extension service and research literature on the impact of stinkbug 

damage to cotton in order to estimate when dicrotophos is likely to be applied in this crop, since 

these insects are the major target pests for this pesticide use. The University of Georgia's 2014 

Cotton Production Guide (UGA 2014) describes stinkbug damage to cotton as follows: 

"Stinkbugs have piercing sucking mouthparts and damage cotton by feeding on the seeds of 

developing bolls. Stink bugs feed by piercing the boll wall with their beak and injecting a 

digestive enzyme into the boll in or near the seed to soften or dissolve plant tissues so the bug 

can remove them. In addition to physical damage, this process allows for entry of rot organisms 

that contributes to degradation of bolls reducing yield and quality. Bolls damaged by stinkbugs 

may show sunken, purple spots on the outside boll wall; however this is not a reliable indicator 

of stinkbug damage. "In addition, "research suggests that in addition to yield loss, excessive 

stinkbug damage can reduce [desirable] fiber quality characteristics." 

This publication also points out that "the number of bolls per plant which are susceptible to stink 

bugs is not constant and varies during the year. The greatest number of susceptible bolls per 

plant generally occurs during weeks 3-5 of bloom." As the season progresses, fewer susceptible 

bolls are present and the treatment threshold is adjusted to allow for more stinkbugs to be present 

before any insecticides are recommended. Many other factors affect the number of bolls 

vulnerable to stinkbug damage, however (e.g., drought), so the treatment scenario is potentially 

complex. This guide also states that "stinkbug infestations are often first observed near field 

edges (especially near a peanut planting). Some innovative growers have chosen to scout and 

treat cotton near field edges independent of the entire field" 

Dicrotophos is one of the few materials considered highly effective against stinkbugs (Ellsworth 

and Brown, 2013; Roberts and Toews, 2014; UGA, 2014; Reisig, 2014). Considering the 

description of damage and migrating behavior (above), it seems reasonable that growers dealing 

with these pests would apply dicrotophos just before bloom or later in the season when they 

detect insects moving in from nearby alternate host plants. This may sometimes coincide with 

bloom (see Table 2). 

The typical application parameters that should be used to reflect actual usage of dicrotophos, 

based on proprietary usage data (Proprietary Pesticide Usage Data, 2008-2012), cotton 

phenology and target pest biology are shown in Table 2 (below). 

Page 4 of9 
Table 2. Recommended application parameters for modeling the use of dicrotophos on MS, NC, 

and TX cotton. 

State Rate Nu..-.berof Method Timing Calendar Dates 

(lb a.i./ A) Applic~tions 

per Season Fint Second 

Application Application 

Mississippi 0.28 2* Ground First at 27 June 27 July 

(MS) pinhead 

squaring, 

Second at 

peak bloom 

North 0.22 1 Ground Pinhead 29 June ---- Carolina squaring 

(NC) 

Texas 0.24 2* Ground First at 27 June 27 July 

(TX) pinhead 

squaring, 

Second at 

·peak bloom 

• Number of applzcatzons 1s rounded up from 1.4 per season based on 2008 to 2012 propnetary pesticide usage 

data. 

TARGET PESTS AND PEST MANAGEMENT IMPORTANCE 

BEAD provides this discussion of the pest management role of dicrotophos and its alternatives 

(section below) with a focus on its use in southeastern states, since these are the regions where 

use appears to be highest, and also include the ones mentioned above (Table 2). However, use of 

dicrotophos and some alternatives against the stinkbug complex, as described below, is also 

applicable to Arizona, where these pests have recently increased in importance (Ellsworth and 

Brown 2013). 

The label for dicrotophos on co~on states that it can be used to control the following insects: 

thrips, cotton fleahoppers, grasshoppers, boll weevils, stinkbugs, and plant bugs (all species). In 

addition, the label states that the following insects can be "suppressed": aphids and spider mites. 

Historically, this insecticide has been used for all these pests (depending on the region or year 

considered). However, proprietary data on the use of dicrotophos in the past five years (2008-

2012) indicates that only the following arthropods have been the targets of usage on 5% of total 

acres treated or more per year (on average): thrips, plant bugs, and stinkbugs. Of these the major 

targets appear to be the tarnished plant bug and stinkbugs (the species described in detail earlier 

in this memo; see page 2). 

Page 5 of9 
DICROTOPHOS ALTERNATIVES 

Recent crop production guides from extension services in major cotton producing states, such as 

Georgia, North Carolina, and Texas, mention dicrotophos as an option to manage the following 

pests: thrips, plant bugs, and stinkbugs (USDA, 2009; Roberts and Toews, 2014; UGA, 2014; 

Reisig, 2014). Tables 3 and 4 (below) show major alternatives to selected target pests, as 

identified by proprietary data. Since growers appear to have mainly focused on stinkbugs and the 

tarnished plant bug in recent years of dicrotophos use, these insects are also the focus of the 

information below. In addition the data show only those alternatives that are also used at the 

same time as dicrotophos during boll development (i.e., the crop stages described in Table 2 

above). 

As stated earlier in this memo, it appears that within the recent "pest spectrum" for dicrotophos 

use, the most important ones are those that comprise the complex of stinkbug species that attack 

cotton bolls. For these insects, few effective alternatives seem to exist, though growers have used 

a variety of materials as described above. The ones currently considered most effective, in 

addition to dicrotophos, are acephate and bifenthrin (alone or together), at maximum label rates, 

and bifenthrin premixed with zeta-cypermethrin (Ellsworth and Brown, 2013). 

RECOMMENDATIONS 

BEAD recommends using the established planting, emergence, and harvest dates for cotton 

(Table 1) and the typical dicrotophos application parameters for rate, number of applications, and 

timing (Table 2). 

Page 6 of9 
Table 3. Alternatives to dicrotophos in use by cotton growers with the same timing as 

dicrotophos (see Table 2 above). This Table shows alternatives for the tarnished plant bug 

only. Only alternatives used on 5 percent or more (total treated acres) are listed, based on 

proprietary data average d . natiOn all ly :tl or the years 2008-2012. 

Insecticide Chemical Class Percent Crop treated * 

Acephate Organophosphate 158 

Thiamethoxam 

N eonicotinoid 85 

Bifenthrin 

Pyrethroid 83 

Imidacloprid Neonicotinoid 60 

Novaluron Chitin biosynthesis inhibitor 39 

(insect growth regulator) 

Lambda-cyhalothrin Pyrethroid 25 

Oxamyl Carbamate 23 

Cypermethrin Pyrethroid 20 

Cyfluthrin Pyrethroid 18 

Flonicamid Nerve action (modulator of 15 

chordotonal organs) 

Dimethoate 

Organophosphate 7 

Zeta-cypermethrin Pyrethroid 6 

*Percent crop treated is based on total acres treated, whzch includes acres treated with more than one 

application. Since these acres are cumulative, some materials show greater than 100 % crop treated 

These data are provided only to show the relative magnitude of use of each alternative, not for risk 

modeling purposes .. 

Page 7 of9 
Table 4. Alternatives to dicrotophos in use by cotton growers with the same timing as 

dicrotophos (see Table 2 above). This Table shows alternatives for the stink bug complex only. 

Only alternatives used on 5 percent or more (total treated acres) are listed, based on proprietary 

d t d a a average na f ton all 1y £ or th e years 2008 -2012 ,., 

'r. Insecticide Chemical Class Percent Crop treated * 

il' 

j -· 

Bifenthrin 

Pyrethroid 100 

Lambda-cyhalothrin Pyrethroid 53 

Cyfluthrin Pyrethroid 43 

Acephate Organophosphate 27 

Zeta-cypermethrin Pyrethroid 27 

Cypermethrin · Pyrethroid 25 

Novaluron Chitin biosynthesis inhibitor 22 

(insect growth regulator) 

Imidacloprid Neonicotinoid 19 

Thiamethoxam 

N eonicotinoid 8 

Clothianidin Neonicotinoid 5 

* Percent crop treated is based on total acres treated, which includes acres treated with more than one 

application. Since these acres are cumulative, some materials show greater than 100 % crop treated 

These data are provided only to show the relative magnitude of use of each alternative, not for risk 

modeling purposes. 

REFERENCES CITED 

APHIS. 2013. Questions and Answers: Boll Weevil Eradication Program. USDA-APHIS 

Factsheet. Available on the web at 

http:/ /www.aphis.usda.gov/publications/plant health/20 13/fag boll weevil erad.pdf 

[Accessed July 2014]. 

Atwood, D. 2012. Review of Benefits for Sulfoxaflor for Fruiting Vegetables, Cucurbit 

Vegetables, Citrus, and Cotton. (DP# 384640). Internal BEAD memorandum available 

through the Official Records database. 

Page 8 of9 
Ellsworth, P. and L. Brown. 2013. Frequently Asked Questions: Brown Stink Bugs. Extension 

factsheet from the University of Arizona Cooperative Extension Service. Available on the 

web at https://cals.arizona.edu/crops/cottonlfiles/BSB FAQlo.pdf [Accessed May 2014] 

Hebert, A., E. Blinka, J. Bacheler, J. VanDuyn, J. Greene, M. Toews, P. Roberts, and R.H. 

Smith. 2009. Managing Stinkbugs in Cotton: research in the Southeast Region. 

Publication# 444-390 of the Virginia Cooperative Extension Service. Available on the 

web at http://pubs.ext.vt.edu/444/444-390/444-390.html [Accessed July 2014]. 

NCCA. 2014 Overview. Integrated Crop Management. Advancing Cotton Education. Online 

publication of the National Cotton Council of America Available on the web at 

http://www.cotton.org/tech!ace/ overview.cfm 

Proprietary Pesticide Usage Data. 2008-2012. 

Reisig, D.D. 2014. Insect Control on Cotton. Pp 78-81 In: 2014 North Carolina Agricultural 

Chemicals Manual. Available on the web at http://fsg.ces.ncsu.edu/publicationlnorthcarolina-agricultural-chemicals-manual/ [Accessed July 2014]. 

Roberts, P.M. and M. Toews. 2014. Cotton Insect Control. Pp 36-41 In: 2014 Georgia Cotton 

Production Guide. Available on the web at www.ugacotton.com. 

Stevenson, D. E. and M.A. Matocha. 2005. A Pest Management Strategic Plan for Cotton 

Production in Texas. Available on the web at www.ipmcenters.org [Accessed June 2014]. 

Stewart, S. and A. McClure. 2013. Insect Control Recommendations for Field Crops: Cotton, 

Soybean, Field Com, Sorghum, Wheat and Pasture. Publication# PB 1768 ofthe 

University of Tennessee Extension. Available on the web at 

https:/ /utextension. tennessee.edu/publications. [Accessed May 2014]. 

UGA. 2014. Cotton Production Guide. Publication# CSS-14-01 ofthe University of Georgia 

College of Agricultural and Environmental Sciences Cooperative Extension. Available on 

the web at www.ugacotton.com. 

USDA. 2009. Crop Profile for Cotton in Texas. Available on the web at www.ipmcenters.org. 

USDA, 2010. Field Crops, Usual Planting and Harvesting Dates. Agricultural Handbook 

Number 628. National Agricultural Statistics Service, United States Department of 

Agriculture. Available on the web at 

http:/ /usdaO 1.library.comell.edu/usda/current/planting/planting-1 0-29-201 O.pdf 

[Accessed August 2014]. 

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