Management of corn earworm and fall armyworm (Lepidoptera : Noctuidae) injury on a sweet corn hybrid expressing a cryIA (b) gene

Research was conducted to evaluate transgenic sweet corn containing a modif ied cryIA(b) gene from Bacillus thuringiensis (Bt) and a minimal number of insecticide applications for management of injury to ears by corn earworm, Helicoverpa tea (Boddie), and fall armyworm, Spodoptera frugiperda (J. E. S mith). GH-0937 (Bt+), Bonus (Bt-), and Silver Queen (Bt-) sweet corn hybrid s 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 t he season. During ear development, methomyl was applied in 0, 1, 3, or 5 ap plications 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 army worm 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 ext ensive 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 insectic ide applications, and 172 and 50 cm(2), respectively, with 5 applications o f methomyl. Injury to ears on GH-0937 was not eliminated, but was minimal a nd confined to a few kernels at the ear tip. Most of the observed injury wa s From feeding by nitidulid beetles, or to an occasional large fall armywor m larva that migrated from a susceptible plant to an untreated ear of GH-09 37 where it fed before trying. Bt sweet corn offers an excellent opportunit y to develop more environmentally compatible approaches for sweet corn prod uction.