Corn plant and seedling insect complex interactions with seed-applied and in-furrow insecticides

A majority of the US corn fields are planted with a seed-applied neonicotinoid-class insecticide. A major objective of these studies was to show the impacts of insecticidal seed treatments on several species of insects in corn and to document the interaction with plant growth characteristics. Two field sites were targeted containing wireworms (Melanotus communis (Gyllenhal), Conoderus vespertinus (F.) and C. lividus (Degeer)) and annual white grubs (Cycloaphala spp.) A third site targeted southern corn billbugs (Sphenophorus callous (Olivier)). Treatments included untreated corn seed, as well as in-furrow and seed-applied insecticides (terbufos 560.424g a.i./ha, clothianidin 3.088mg a.i./ha, clothianidin 1.235mg a.i./ha, terbufos 560.424g a.i./ha + clothianidin 3.088mg a.i./ha, terbufos 560.424g a.i./ha + clothianidin 1.235mg a.i./ha, bifenthrin 448.339g a.i./ha). Above-ground injury and root injury were assessed from the two non-billbug locations at two, three, and four weeks after planting. Root weights were taken from the samples collected at one of these locations and soil was sifted from each plot to document soil-dwelling insect pest density. Wireworms were counted from root samples at the other location. At the billbug location, injury was observed two, three, and four weeks after planting. Seedlings with neonicotinoid seed treatments had fewer wireworms, greater root mass, and less billbug injury compared to seedlings that had no seed treatment, either with or without in-furrow insecticides. Insecticidal seed treatments provided a benefit in plant growth metrics, with less injury and associated insect abundances. Future studies will examine the clothianidin concentration in the plant at the feeding sites of wireworms and billbugs.