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

A majority of the US corn is planted with a seed-applied neonicotinoid-class insecticide. Our objective was to show the impact of a common insecticidal seed treatment (clothianidin) compared to common in-furrow insecticides on several species of seedling-pest insects in corn and to document interactions with plant growth and clothianidin uptake in the zone of feeding. Studies were conducted from 2014-2015 in field sites containing wireworms (Melanotus communis (Gyllenhal), Conoderus vespertinus (F.) and C. lividus (Degeer)) white grubs (Cycloaphala spp., Popillia japonica (Newman), and Cotinis nitida (Linnaeus)), or 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 and coleoptile were taken from the samples collected at both wireworm and billbug locations; wireworm density was documented, when they were present. Injury was assessed at all locations. Seedlings with clothianidin seed treatments had fewer wireworms and less billbug injury compared to untreated seedlings. Clothianidin increased root weight and reduced injury in the presence of white grubs and wireworms. 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. Clothianidin consistently provided more protection compared to the in-furrow insecticides.