UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C., 20460 

APR 0 7 Z014 

MEMORANDUM 

OFFICE OF CHEMICAL SAFETY 

AND POLLUTION PREVENTION 

SUBJECT: Characterization ofCyromazine Use as a Seed Treatment for Commercial Bulb 

Onion Production for Onion Maggot Control 

FROM: Colwell A. Cook~ Biological Analysis Branch ~ 

Elizabeth Hill v ~ lN\._ l~ Economic Analysis Branch 

Jihad Alsadek v v~ 

'-l ,7 /f-.. ~[ 

Science Information Analysis Branch 

Biological and Economic Analysis Division 

THRU: Arnet Jones, Chief 

Biological Analysis Branc 

Timothy Kiely, Chief (J__ \1\Jv\,_ J 

Economic Analysis Branch ~ j _v 6 

Diann 

Science 

Sims, 

Information 

Chief 

Analysis 

~ Branch 

Biological and Economic Analysis Division 

TO: James Parker, Chemical Review Manager 

RMIBI 

Pesticide Re-Evaluation Division 

PRP Review: April3, 2014 

Rationale 

Cyromazine is in the process of undergoing reregistration review. During this process, the 

preliminary risk assessment conducted by the Environmental Fate and Effects Division (EFED) 

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identified risks of concern to passerine birds from the seed treatments to onions. Seed treatments 

for specialty crops are not captured in usage databases available to the Biological and Economic 

Analysis Division (BEAD). This Memorandum discusses the importance of cyromazine as a 

bulb onion seed treatment in commercial production for the control of onion maggots. Because 

of limited data, this is only a qualitative description. 

The Pest 

The primary insect pest in several of the bulb onion producing areas is the onion maggot, Delia 

antiqua (Meigen). These small flies have white larvae that burrow into the developing onion 

bulbs (Davidson and Lyon, 1987; Straub and Eckenrode, 2013). This damage causes the plants 

to die, or makes the bulbs worthless. Depending on the location in the country there can be two 

or more generations per year. Usually the first generation's larvae are the most damaging-- first 

by being the most numerous and second, by attacking the early developing bulbs, thereby 

reducing stand establishment (USDA, 1999). Stand establishment may be reduced from first 

generation maggots anywhere from 10% to 90% (USDA, 1999). 

Because of the flight mobility of the adult insects, foliar applications of many insecticides are not 

very effective. The focus of growers in the regions where these flies are prevalent is on treating 

at plant, either the soil, or the seed, or usually both, 

Use of Cyromazine as a Seed Treatment for Bulb Onions 

Most bulb onion acreage is drill seeded in the Great Lakes Region, Washington, Oregon, Idaho, 

and California (Nault, 2014; Belles, et al., 2014) 

Cyromazine, an insect growth regulator, may be applied to onion seeds by only licensed 

commercial seed treatment companies. In addition, treated seed may be used only in commercial 

bulb onion production. In the past, cyromazine treated seed was commonly used in areas with 

high onion and/or seed com maggots, mainly in the Great Lakes regions (Nault, 2014) and parts 

of California (Belles, et al., 2014). In heavily infested areas cyromazine was used in conjunction 

with chlorpyrifos. While onion maggots in some areas have developed resistance to 

chlorpyrifos, the combination still provides good early season control (Nault, 2014). 

In 2012, two different product combinations became available for onion seeds. One onion 

treatment combines thiamethoxam and spinosad (FarMore F1500®); the other treatment 

combines clothianidin and imidacloprid (Sepresto®). These two combinations are currently the 

treatment of choice by most commercial bulb onion growers in the regions with onion maggots 

and seed com maggots (Nault, 2014). 

Onion seed maggots have been demonstrated to develop resistance to insecticides in the past 

(Nault, 2014; Levey, 2014). While cyromazine usage as an onion seed treatment has declined in 

the last two years, entomologists consider it a valuable chemistry for resistance management in 

the commercial bulb onion growing regions where maggots are pests. (Nault, 2014; Belles, et 

al., 2014) 

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References: 

Belles, D., R Ehn, R Wilson, H Schwartz, M Thornton, D Alston, D Walsh, and T Waters. 2014. 

(Western IPM Center representing AZ, CA, CO, ID, UT, WA). Personal communication 

through USDA/ARS/OPMP. February 25, 2014. 

Davidson, RH and WF Lyon. 1987. Insect Pests of Farm, Garden, and Orchard, 8th edition. 

John Wiley & Sons, New York. 618 pg. 

Levey, C. Syngenta. 2014. Personal Communication to PRD, March 6, 2014. 

Nault, Brian. 2014. Department of Entomology, Cornell University. Personal Communication 

through USDA/ARS/OPMP. February 25, 2014. 

Straub, RW and CJ Eckenrode. 2013. Onion Arthropod Pest Management. In Radcliffe's IPM 

World Textbook. Located at: http://ipmworld.umn.edu/chapters/straub.htm. Accessed: 

3/26/2014. 

USDA. 1999. Crop Profile for Onions in New York. Located at: 

http:/ /www.ipmcenters.org/cropprofiles/docs/nyonions.pdf Accessed: 3/4/2014. 

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