Alternative Controls for Helicoverpazea on Sweet Corn: Phytotoxicity and Pollination Inhibition from Direct Silk Applications

Helicoverpa zea, Boddie (corn earworm) is an important pest of sweet corn in New England. Conventional management of this pest is achieved through repeated applications of chemical insecticides. Organic growers have few alternatives to prevent corn eanvorm infestation as materials such as Bacillus thuringiensis subsp. kurstaki products that are cleared for use in organic production are not very effective against corn earworm when applied with a sprayer. Technology first developed in the 1930\u27s and 1940\u27s using direct-silk applications of mineral oil and insecticides seemed to have some efficacy against corn earworm. The oil caused asphyxiation of early instar larvae traveling down the silk channel to the tip of the ear to feed. This technique has been further researched in the last decade using vegetable oils, though pollination problems associated with these treatments have been observed. Several materials were tested for efficacy against corn earworm and phytotoxicity to the developing ear. Materials tested were corn oil, soy oil, corn oil mixed with B.t., soy oil mixed with B.t., carageenan, and carageenan mixed with B.t. All were compared to an untreated control. None of these treatments effectively controlled corn earworm populations, especially during high-pressure seasons. The oil and B.t. combinations did provide some reduction in infestation (33%) as compared to the untreated controls (97%), but this is inadequate for all wholesale markets, and probably most retail markets as well. Oil-based treatments also caused significant injury to developing ears by inhibiting pollination of the kernels at the tips. This condition, known as cone tip is of primary concern since it may decrease marketability as well. The carageenan-based treatments, while not significantly better than the untreated controls, did not cause the same phytotoxicity seen with the oil treatments