Gerald W. Echtenkamp

Effects of Manure, Hybrid Root Strength, and Reduced Rates of Insecticide on Corn Rootworm (Coleoptera: Chrysomelidae) Injury to Corn

ABSTRACT Field studies were conducted at the Haskell Agricultural Laboratory, University of Nebraska, Concord, NE during 1996, 1997, and 1999 to evaluate the effects of manure application, hybrid root strength, and reduced insecticide rates on corn rootworm (Diabrotica virgifera virgifera LeConte and D. barberi Smith and Lawrence) larval injury and corn (Zea mays L.) yield. Treatment combinations consisted of two corn hybrids, three manure rates (0, 67, and 135 MT/ha), and 4 in secticide rates (0, 2.8, 5.6, and 11.2 g (AI)/100 m-row terbufos, T-band). Overall, manure reduced root injury 7% to 11% and increased yield 1% to 8%. All insecticide rates reduced root injury, but did not affect yield. When manure was combined with insecticide applications, there was no significant increase in root injury protection over that provided by the insecticide. Hybrid root strength did not contribute to root or yield protection. Root injury was relatively low during all years of the study (control root ratings < 4). Manure application did not interfere with the terbofos application. More detailed studies are required to characterize the effects and joint effects of manure application, hybrid root strength, and reduced insecticide rates on rootworm feeding and plant response.