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.

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### ~ Elizabeth Hill

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## ~[ Jihad Alsadek 

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.. Science Information Analysis Branch Biological and Economic Analysis Division
THRU: Arnet Jones, Chief Biological Analysis Branc Timothy Kiely, Chief 

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Diann Sims, Chief

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TO: James Parker, Chemical Review Manager RMIBI Pesticide Re-Evaluation Division


### PRP Review: April3, 2014 Rationale Cyromazine is inthe process ofundergoing reregistration review. During this process, the preliminary risk assessment conducted bythe Environmental Fate and Effects Division (EFED)
1identified risks ofconcern to passerine birds from the seedtreatments 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 ofcyromazine as a bulb onion seed treatment in commercial production for the control ofonion maggots. Because oflimited data, this is only a qualitative description. 

### ThePest The primary insect pest in several ofthe bulb onion producing areas is the onion maggot, Delia antiqua (Meigen). These small flies have white larvae thatburrow into the developing onion bulbs (Davidson and Lyon, 1987; Straub and Eckenrode, 2013). This damage causes the plants to die, ormakes the bulbs worthless. Depending onthe location in the country there canbe two ormore generations peryear. 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 ofthe flight mobility ofthe adult insects, foliar applications ofmany insecticides are not very effective. The focus ofgrowers in the regions where these flies are prevalent is ontreating at plant, eitherthe soil, orthe seed, orusually both, 

### Use ofCyromazine 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 onionproduction. Inthe past, cyromazine treated seed was commonly used in areas with high onion and/or seed com maggots, mainly inthe Great Lakes regions (Nault, 2014) andparts ofCalifornia (Belles, et al., 2014). Inheavily 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 othertreatment combines clothianidin and imidacloprid (Sepresto®). These two combinations are currently the treatment ofchoice by most commercial bulb onion growers inthe regions with onion maggots and seed commaggots (Nault, 2014). Onion seed maggots have been demonstratedto develop resistance to insecticides inthe 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)

2References: Belles, D., R Ehn, R Wilson, H Schwartz, M Thornton, D Alston, D Walsh, and T Waters. 2014. (Western IPM Centerrepresenting AZ, CA, CO, ID, UT, WA). Personal communication through USDA/ARS/OPMP. February 25, 2014. Davidson, RH and WF Lyon. 1987. Insect Pests ofFarm, 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 ofEntomology, Cornell University. Personal Communication through USDA/ARS/OPMP. February 25, 2014. Straub, RW and CJ Eckenrode. 2013. Onion Arthropod Pest Management. InRadcliffe's IPM World Textbook. Located at: http://ipmworld.umn.edu/chapters/straub.htm
. Accessed: 3/26/2014. USDA. 1999. Crop Profile for Onions inNew York. Located at: http:/ /www.ipmcenters.org/cropprofiles/docs/nyonions.pdfAccessed: 3/4/2014.



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