Effect of foxtail infestation on corn rootworm larvae (Coleoptera:Chrysomelidae) under two corn-planting dates

The impact of foxtail (Setaria spp.) infestations on corn rootworm (Diabrotica spp.) populations was studied in corn planted in early May and early June during 1981, 1982, and 1983. Delaying corn planting significantly reduced corn rootworm larval and adult populations in both foxtail-infested and weed-free corn rootworm larval and adult populations in both foxtail-infested and weed-free corn plots. Compared with weed-free corn plots, weedy plots had significantly fewer corn rootworm larvae and adults in 1 of 3 years and numerically fewer in 3 years. Regression analysis was used to investigate adult corn rootworm emergence in 1981. Delaying corn planting significantly delayed 50% occurrence of corn rootworm adults. Foxtail infestation also delayed corn rootworm emergence, but differences were nonsignificant. The interaction of alternate food sources (foxtail) and weed competition on corn plant growth and corn rootworm food availability is discussed.