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. Our objective was to show the impacts of insecticidal seed treatments on several species of insects in corn and to document interactions with plant growth. 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 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 non-billbug locations. Root weights and concentrations of clothianidin at the mesocotyl were taken from the samples collected at one of these locations; soil was sifted from each plot to document soil-dwelling insect pest density at wireworm locations. Injury was assessed at the billbug location. Seedlings with neonicotinoid seed treatments had fewer wireworms, greater root mass, and less billbug injury compared to untreated seedlings. Clothianidin concentration in the mesocotyl was highest in treatments with 3.088mg a.i./ha, intermediate in treatments with 1.235mg a.i./ha, and lowest with untreated seed.