Evaluation of Oils and Microbial Pathogens for Control of Lepidopteran Pests of Sweet Corn in New England

Vegetable and mineral oil, Beauveria bassiana (Balsamo) and Bacillus thuringiensis subsp. kurstaki Berliner were evaluated for control of Ostrinia nubilalis (Hübner) (Lepidoptera: Pyralidae), Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae) and Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae) in sweet corn (Zea mays L.). Field experiments in Maine and Massachusetts during 1993 and 1994 evaluated oils and pathogens singly or in combinations, using a single application directly to the top of the silk channel, immediately after pollination. Mineral oil alone provided equal (1993) or better (1994) control compared with corn oil. In both years, mineral or corn oil plus B. thuringiensis resulted in 93-98% marketable ears, compared with 48-52% marketable ears in untreated plots. In three factorial experiments with B. bassiana, B. thuringiensis and corn oil, B. bassiana at 5 x 10(7) conidia per ear provided little or no control while B. thuringiensis and corn oil provided significant though not always consistent control of all three species. The combination of B. thuringiensis and corn oil provided the largest and most consistent reduction in numbers of larvae and feeding damage to ears.