Seed coating technologies and treatments for onion: Challenges and progress

Conventional methods to control the onion maggot or onion fly, Delia antiqu a (Meigen), have relied on in-furrow applications of the toxicant pesticide , chlorpyrifos. The objective of this research was to develop an onion (All ium cepa L.) seed treatment that utilizes a new chemistry compound that is environmentally safe. Cyromazine is an insect growth regulator with a mode of action different from traditional pesticides used to control onion maggo t. Cyromazine has low mammalian toxicity and is relatively nontoxic to othe r insects, including beneficials. High seed loading rates (50 g.kg(-1) acti ve ingredient) are required for optimal efficacy, and conventional slurry m ethods are inadequate to apply these high loading rates. Film coating and p elleting were performed at Cornell Univ. to apply cyromazine and a register ed fungicide (a formulation of thiram and carboxin) to onion seeds. Results of field studies performed over several years revealed that stand losses d ue to the onion maggot ranged from approximate to 20% to 60%. Cyromazine ap plied by either film coating or pelleting decreased the loss by onion maggo t from 1% to 8%,and efficacy was comparable to an In-furrow application of chlorpyrifos. Cyromazine was registered as a seed treatment and is commerci ally used in the northeastern and midwestern United States, where onion mag got is a serious pest. Field emergence was not negatively affected by cyrom azine coated onto the seeds when onion seeds are sown in organic (muck) soi ls. There is other evidence, however, that cyromazine seed treatments may c ause phytotoxicity to germination and seedling growth. Testing seed quality in sand or on roll towels revealed a high percentage of abnormal seedlings . Retarded root growth was observed in seeds treated with cyromazine, resul ting in an increase in abnormal seedling classifications. a finely ground s phagnum peatmoss applied over the seeds in a roll towel test ameliorated th e abnormal root growth symptoms, and seedling had robust growth. Collective ly, film coating and pelleting were effective delivery systems for the appl ication of plant protectants required at time of sowing. Modification of th e standard germination test was needed to accurately assess onion seed qual ity. Moreover, this project was successful due to a team Effort of a univer sity seed scientist and entomologists working with onion growers and indust ry. Future registrations on small acreage, high-value horticultural crops a re envisioned to require similar multi-partner approaches. Chemical name us ed: N-cyclopropyl-1,3,5-triazine-2,4,6-triamine (cyromazine).