Date of Award

1997

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Entomology

First Advisor

Seth J. Johnson

Abstract

Population density estimates, yield data, damage rating, and marketability of cabbage were used to assess the effectiveness of integrating several control tactics--an action threshold, host plant resistance, intercropping (companion planting), microbial control, and pesticide use reduction--for managing the diamondback moth (DBM), Plutella xylostella (L.), and the cabbage looper (CL), Trichoplusia ni (Hubner), in cabbage and in protecting beneficial arthropods. An action threshold of six DBM larvae per plant was inadequate for making insecticide application decisions because cabbage plots treated based on this action threshold had significantly higher densities of CL and DBM larvae, higher damage rating and yield loss, and lower damage-free yield and percentage of marketable cabbage compared with plots treated weekly. A new cabbage hybrid, Tropicana, was superior to two other varieties, KY Cross and Early Jersey, in resisting attack from DBM. The role of intercropping (companion planting) in insect control was inconclusive. Agree 50 WP$\sp\circler$ and WG$\sp\circler$, microbial insecticides based on toxins of Bacillus thuringiensis Berliner, gave excellent results in controlling CL and DBM. Also, significant and favorable interactions between the bioinsecticide and the Tropicana cabbage variety indicated that they may be compatibly combined for DBM management. In addition, field results confirmed the potential of incorporating pesticide use reduction in management programs for lepidopteran pests of cabbage; plots treated at 25 and 50% of the recommended rates of Agree 50 WG$\sp\circler$, Ambush 2 EC$\sp\circler$, and Malathion 50$\sp\circler$ had essentially the same level of CL and DBM larval infestation, damage rating, and percentage of marketable cabbage as those treated at the recommended rates. Perhaps because only those actually in the canopy of plants were counted, population levels of generalist predators were generally low in treatment plots such that clear-cut treatment effects were not observed. These results indicate that, within the context of the pest management problems that have arisen because of the reliance on conventional insecticides as the sole control strategy for CL and DBM, IPM programs incorporating host plant resistance, microbial control, and pesticide use reduction may lead to a more sustainable management system for these pests.

ISBN

9780591614558

Pages

201

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