Performance of novel insecticide seed treatments for managing onion maggot (Diptera: Anthomyiidae) in onion fields

Management of onion maggot, Delia antiqua (Meigen), in onion requires the use of an insecticide applied at planting. Insecticide resistance and a dearth of available products have stimulated an effort to identify new insecticides for onion maggot control, especially chemistries that can be delivered as seed treatments. Onion seeds film-coated with fipronil, spinosad, clothianidin or thiamethoxam were evaluated for onion maggot control in muck soils located in two major onion-growing regions in New York, USA in 2001–2003. Fipronil, spinosad and clothianidin at rates of 25, 25 and 50 g (a.i.)/kg of seed, respectively, consistently provided excellent control of onion maggot (⩽5% seedling loss). Moreover, these seed treatments performed well during wet and dry seasons. In contrast, thiamethoxam at a rate of 50 g (a.i.)/kg of seed failed to control onion maggot in three of the five experiments. Cyromazine seed treatment, which is currently used by onion growers, provided an equivalent level of onion maggot control to fipronil, spinosad and clothianidin. The other commonly used treatment, chlorpyrifos in-furrow drench, performed poorly in three of the four experiments, resulting in an average seedling loss of 17%. Insecticide resistance was implicated as the reason for the failure in two of the trials where seedling loss averaged 24%. Seed treatments provide growers with a convenient, reliable and environmentally responsible method for managing economically damaging onion maggot infestations, including those that are resistant to chlorpyrifos. Fipronil, spinosad and clothianidin seed treatments should be considered for future registration on onion. Availability of these chemistries would allow rotation with the cyromazine seed treatment, which would likely prolong the longevity of all products.