Management of Corn Earworm and Fall Armyworm (Lepidoptera: Noctuidae) Injury on a Sweet Corn Hybrid Expressing a cryIA(b) Gene

Abstract

Research was conducted to evaluate transgenic sweet corn containing a modified cryIA (b) gene from Bacillus thuringiensis (Bt) and a minimal number of insecticide applications for management of injury to ears by corn earworm, Helicoverpa zea (Boddie), and fall armyworm, Spodoptera frugiperda (J. E. Smith). GH-0937 (Bt+), Bonus (Bt-), and Silver Queen (Bt-) sweet corn hybrids were planted 15 April, 1 May, 15 May, 1 June, and 15 June 1997 to provide different intensities of insect pressure as populations increased during the season. During ear development, methomyl was applied in 0, 1, 3, or 5 applications beginning when 50% of the plants were silking. GH-0937 exhibited a high level of resistance to leaf feeding in the whorl stage by fall armyworm and to ear injury by the corn earworm and fall armyworm. With extreme insect pressure on plants for the 15 June planting, as evidenced by the extensive damage to Bonus and Silver Queen in the whorl stage, injury to ears of GH-0937 averaged only 7.9 cm 2 of kernel damage when no insecticide was applied, and was reduced to an average of only 1.7 cm 2 of kernel damage with 5 applications of methomyl. In this same test, Silver Queen and Bonus averaged 323 and 168 cm 2 of kernel damage, respectively, with no insecticide applications, and 172 and 50 cm 2 , respectively, with 5 applications of methomyl. Injury to ears on GH-0937 was not eliminated, but was minimal and confined to a few kernels at the ear tip. Most of the observed injury was from feeding by nitidulid beetles, or to an occasional large fall armyworm larva that migrated from a susceptible plant to an untreated ear of GH-0937 where it fed before dying. Bt sweet corn offers an excellent opportunity to develop more environmentally compatible approaches for sweet corn production.