Direct Silk Applications of Corn Oil and Bacillus thuringiensis as a Barrier to Corn Earworm Larvae in Sweet Corn

in HortTechnology

Field studies were conducted in 2000 and 2001 to rate the efficacy and longevity of four pesticide treatments against corn earworm (Helicoverpa zea) larvae (CEW) in sweet corn (Zea mays). The four treatments used were 1) corn oil, 2) Bacillus thuringiensis ssp. kurstaki (Bt), 3) oil + Bt, and 4) an untreated plot. All treatments were applied on silk day 5. Silk day 1 was the first day that more than 50% of the ears had 2.5 cm (1 inch) or more silks emerging from the husk using a hand-held pump applicator. Two first-instar CEW larvae were placed directly into silk channel of selected ears on 6 different days (days 3, 6, 9, 12, 15, and 18 after first silk). The same six ears were then harvested 4 days later. Untreated ears had more live CEW and higher levels of feeding damage than the other three treatments ears for all harvest days in both years. The number of CEW found per ear was lower when Bt was included in the treatment. The use of corn oil gave the lowest damage ratings on almost all harvest days in both years. Treatments which contained oil had the highest number of marketable ears in both years, but also the highest percentage of underdeveloped kernels at the tip of the ear (6% to 9%). The oil and Bt treatments appeared to control CEW for at least 17 days, from silking through maturity. This treatment regime appears to be a promising alternative for growers to conventional pest management methods.

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Contributor Notes

Corresponding author; e-mail akcarter@pssci.umass.edu.e-mail rhazzard@umext.umass.edu.

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