Entomopathogenic Nematodes for Field Control of Onion Maggot (Delia antiqua) and Compatibility with Seed Treatments

SIMPLE SUMMARY: Onion maggot (Delia antiqua) can be a devastating pest of onion and related crops around the world. While management of this pest typically relies on insecticides to control these pests, growing resistance and desire for alternative control strategies has motivated a search for new methods to manage them effectively. We investigated the potential of using tiny beneficial roundworms called entomopathogenic nematodes to control onion maggots. We conducted surveys in onion-growing areas to see if these nematodes were naturally present, and also tested their compatibility with commonly used insecticides. Our field trials demonstrated that applying entomopathogenic nematodes can significantly reduce the number of onion plants destroyed by onion maggots, leading to higher crop yields. These nematodes could be a useful tool for onion farmers, whether they practice conventional or organic farming. When combined with other strategies like insecticide seed treatments, the use of entomopathogenic nematodes can provide effective control of onion maggots while boosting crop productivity. ABSTRACT: Onion maggot (Delia antiqua) is a prominent pest of allium crops in temperate zones worldwide. Management of this pest relies on prophylactic insecticide applications at planting that target the first generation. Because effective options are limited, growers are interested in novel tactics such as deployment of entomopathogenic nematodes. We surveyed muck soils where onions are typically grown to determine if entomopathogenic nematode species were present, and then evaluated the compatibility of entomopathogenic nematode species with the insecticides commonly used to manage D. antiqua. We also evaluated the efficacy of these entomopathogenic nematodes for reducing D. antiqua infestations in the field. No endemic entomopathogenic nematodes were detected in surveys of muck fields in New York. Compatibility assays indicated that, although insecticides such as spinosad and, to some extent, cyromazine did cause mortality of entomopathogenic nematodes, these insecticides did not affect infectivity of the entomopathogenic nematodes. Field trials indicated that applications of entomopathogenic nematodes can reduce the percentage of onion plants killed by D. antiqua from 6% to 30%. Entomopathogenic nematodes reduced D. antiqua damage and increased end of season yield over two field seasons. Applications of entomopathogenic nematodes may be a viable option for reducing D. antiqua populations in conventional and organic systems. Together with other management tactics, like insecticide seed treatments, applications of entomopathogenic nematodes can provide a yield boost and a commercially acceptable level of D. antiqua control.