EFFECT OF BACILLUS-THURINGIENSIS APPLICATION INTERVAL ON EUROPEAN CORN-BORER (LEPIDOPTERA, PYRALIDAE) CONTROL IN SWEET CORN

Ground-applied treatments of two commercial Bacillus thuringiensis sub sp. kurstaki formulations (MVP and Dipel ES) and tank mixes with a pyr ethroid (Ambush 2E) were evaluated for control of European corn borer, Ostrinia nubilalis (Hubner), larvae in sweet corn. Treatments were ap plied at average intervals of 3.4, 5, 7, and 10 days to determine fiel d persistence. Manual infestations of first-instar O. nubilalis were u sed to augment natural populations. During both years, there were no s ignificant interactions between application interval and treatment for all dependent variables tested, including late instars per ear, perce nt marketability, yield, and predator density. Regardless of applicati on interval, MVP provided greater larval control than Dipel ES. Howeve r, the decline in efficacy of the encapsulated MVP formulation occurre d at the same rate as that of the nonencapsulated Dipel ES formulation over the 3.4 to 10-d intervals. Tank-mixes of B. thuringiensis + low- rate permethrin provided no additional control compared with low-rate permethrin alone. Given the infestation levels present in this test, n either B. thuringiensis formulation provided control sufficient to mai ntain current processor standards of 5-10% infested ears at harvest.