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Evaluation of Harpin for the Control of Insect-Vectored Bacterial Wilt of Pumpkin and Comparison of Cucurbit Crop Types and Cultivars for their Attractiveness to Cucumber Beetles and Susceptibility to Bacterial Wilt 2000

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Principal Investigators: Margaret Tuttle McGrath, Dept. of Plant Pathology, Riverhead; Steven V. Beer, Dept. of Plant Pathology, Ithaca

Cooperators: Daniel Gilrien, Entomologist, CCE Suffolk County; Thomas A. Zitter, Dept. of Plant Pathology, Ithaca

Abstract:

Recently there has been a dramatic increase in the occurrence of bacterial wilt, especially in pumpkin and squash, not only in New York, but also elsewhere in the U.S. The bacterium causing this disease (Erwinia tracheiphila) cannot be controlled directly with pesticides, therefore, management practices have targeted the insects that harbor and vector the pathogen, which are the striped and spotted cucumber beetles. Application of insecticides is the main management practice being used. The goals of this project, which was started in 1999, were 1) to determine if harpin can reduce beetle infestations and/or the occurrence of wilt and 2) to compare cucurbit crop types and cultivars for their attractiveness to cucumber beetles and susceptibility to wilt. Unfortunately, harpin does not appear to an effective tool for managing beetles or wilt in a highly wilt-susceptible pumpkin cultivar. It may be effective with other cucurbit crops.

This study provides growers with useful information about differences among cucurbit crop types and cultivars in attractiveness to cucumber beetles and susceptibility to bacterial wilt. It can be implemented now. With this information, growers can adjust their management program for cucumber beetles and wilt, thereby increasing their profitability and reducing insecticide use with some cultivars. For example, the pickling cucumber Country Fair was considerably less susceptible than the pickling cucumber Calypso and the slicer Dasher II, even under the high insect and disease pressure that occurred in this experiment. It could be grown without applying insecticides for cucumber beetles. On the other hand, the gourd Turk's Turban was very attractive to beetles and highly susceptible to wilt. Growers have complained that plants of this cultivar tend to die prematurely; results from this work reveal why. A more intensive insecticide program needs to be used with this cultivar where wilt occurs. Two pumpkin cultivars with resistance to powdery mildew (PMR) were more susceptible to wilt than other pumpkin cultivars. Fortunately there does not appear to be a general correlation between wilt susceptibility and PMR as the PMR muskmelon and yellow summer squash cultivars examined in this study were not more susceptible to wilt than the other cultivars examined. Waltham Butternut was less susceptible to wilt than other winter squash cultivars examined. Watermelon was less susceptible than other cucurbit crops. There will be no cost to implement the findings of this project unless the seed of a less susceptible cultivar is more expensive than others or a more susceptible cultivar is selected for its horticultural characteristics necessitating that a more intensive insecticide program be used.