Neem products for the control of the European corn borer, Ostrinia nubilalis (Hubner), in sweet corn, Zea mays (L.).

The use of neem products to control the European corn borer, Ostrinia nubilalis (Hubner), in sweet corn was investigated. Three years of field studies were conducted comparing various foliar-spray applications of a neem seed kernel extract (NSKE), azadirachtin (AZA, the active ingredient of neem extracts), and Ambush (a synthetic pyrethroid). The results included: (1) NSKE sprayed prior to artificial infestation of the corn plants provided excellent protection (comparable to Ambush) against borer damage and greatly reduced larval populations. (2) Neem extract formulations from Safer Ltd. were the most effective. (3) The rate of application or number of applications were not determining factors in altering the efficacy of neem products. (4) Exceptional weather conditions (high temperatures, dry conditions) may be detrimental to the efficacy of foliar applied neem products. (5) Some neem treatments were found to increase corn stalk breakage possibly by altering the behavior of the larvae. Laboratory evaluations using no-choice leaf-disk bioassays showed the antifeedant action of AZA and the negligible effect of PBO (piperonyl butoxide) and Citowett (used in field formulations) on the feeding behavior of 3rd instar larvae. Growth and development studies of O. nubilalis fed a diet containing 0, 1, 3, 10, 30, 100, and 1000 $\mu$g NSKE g$\sp{-1}$ diet were conducted. 10 $\mu$g NSKE g$\sp{-1}$ diet (50 ng AZA g$\sp{-1}$ diet) fed continuously to the larvae were larvicidal and concentrations as low as 3 $\mu$g NSKE g$\sp{-1}$ diet (16.6 ng AZA g$\sp{-1}$ diet) significantly reduced larval, pupal and adult weights, increased the larval and pupal periods, decreased adult emergence and caused wing deformities. AZA content of the extracts was found to be a critical factor in the IGR (insect growth regulator) effects of NSKE. (Abstract shortened by UMI.)