Phytotoxicity and Pollination Disorders in Sweet Corn Due to Direct-silk Applications of Materials Used for Alternative Corn Earworm Control
2007
Jackson, T.L. | Hutton, M.G. | Handley, D.T.
Corn earworm CEW (Helicoverpa zea) is one of the most important pests of sweet corn (Zea mays) in New England. Conventional management of this pest is achieved through repeated applications of chemical insecticides through the silking period. Organic growers, however, have few alternatives to prevent CEW infestation. Technology first developed in the 1930s and 1940s, using applications of mineral oil directly into the silk channel with an eyedropper, has been further researched in recent years using vegetable oils with and without pesticides, but pollination problems associated with these treatments have been observed. Several materials were evaluated for efficacy in controlling CEW populations and for phytotoxicity to the developing ear. Materials evaluated were corn oil, soy oil, carrageenan, corn oil mixed with Bacillus thuringiensis ssp. kurstaki (Bt), soy oil mixed with Bt, and carrageenan mixed with Bt. All treatments were compared with an untreated control. Treatments provided a range of 33% to 50% control of CEW infestation. The oil and Bt combinations provided some reduction in infestation compared with the untreated controls (33% vs. 100% infestation), but this level of control was inadequate for all wholesale markets and most direct markets. Additionally, oil-based treatments also caused significant injury to developing ears by reducing pollination quality, impacting the development of the kernels at the ear tip. This condition referred to as "cone-tip" is of concern since it may decrease marketability. The percent unmarketable ears due to cone-tips ranged from 0% to 13% for the untreated and carrageenan-based treatments. From 12% to 42% of ears were unmarketable due to the soy oil treatments. Corn oil treatments caused 10% to 50% cone-tips.
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