Wireworm management I: stand protection versus wireworm mortality with wheat seed treatments

The efficacy of various insecticidal seed treatments in protecting wheat, Triticum aestivum L., from wireworm damage as well as reducing wireworm (Coleoptera: Elateridae) populations was studied over 3 yr. Protection from wireworm damage was measured by postplanting stand counts, and effects on wireworm populations were measured by within-row core samples and by bait traps placed in plots the following spring. The effects of treatments on populations of larger wireworms already present at planting were distinguished from their effects on neonate wireworms produced that growing season. Neonicotinoid seed treatments (imidacloprid, clothianidin, and thiamethoxam) provided excellent wheat stand protection, likely through prolonged wireworm intoxication, but populations of larger and neonate wireworms were not significantly reduced in bait traps the following spring. The pyrethroid tefluthrin, applied to seed with and without a neonicotinoid insecticide (thiamethoxam), provided excellent crop protection, but populations of wireworms also were not significantly reduced. This and additional laboratory data suggest that wheat stand establishment provided by tefluthrin is due to a combination of repulsion and short term morbidity events. The phenyl pyrazole fipronil provided excellent crop protection, and populations of both larger and neonate wireworms could not be detected in plots the following spring. The previously registered organochlorine lindane, although reducing wireworm feeding, was phytotoxic in 2 of 3 yr. Next to fipronil, lindane was the most consistent seed treatment in reducing populations of larger and neonate wireworms. These studies indicate that stand and yield protection provided by contemporary wheat seed treatments cannot automatically be equated with wireworm population mortality. This is an important consideration when choosing a suitable seed treatment to replace lindane, which historically provided both stand protection and wireworm reduction, and did not have to be applied every year.