Muskmelon Diseases

The Melcast disease warning system, developed at Purdue University by Dr. Richard Latin, proved its value for managing anthracnose (pathogen: Colletotrichum orbiculare) with fewer sprays than a conventional program of spraying every 2 weeks after vine touch. We also evaluated the reliability of substituting remotely estimated wetness and temperature data for on-site measurements in implementing Melcast, in collaboration with Dr. Terry Gillespie of the University of Guelph, Canada.

With weed ecologist Matt Liebman of ISU, we evaluated weed management using a hairy vetch/ryegrass cover crop as a substitute for conventional herbicides. After multiple sites and years of trials, we concluded that this strategy was not practical for Iowa due to inadequate weed control and the fact that using the cover crop delayed planting by 2-4 weeks, which reduced the sale price of melons.

In cooperation with Bill Hutchison and Eric Burkness at the University of Minnesota, Whitney Cranshaw at Colorado State University, and David Hougen-Eitzman at Carlton College, we evaluated evaluating several strategies for management of striped and spotted cucumber beetles and the disease they vector, bacterial wilt (Erwinia tracheiphila). These strategies included trap-and-kill, a semiochemical-based system for monitoring beetles, several low-impact insecticides, row covers, and trap crops. Of these strategies, row covers appeared to be the most consistently beneficial for muskmelons in Iowa. In Iowa field trials, row covers suppressed bacterial wilt incidence and severity throughout the season, even though they were in place only from transplanting until bloom, and enhanced yield. A report of the row cover results has been submitted for publication in Plant Health Progress.

Lack of knowledge of the ecology of bacterial wilt handicaps efforts to improve management of this important disease. The difficulty of isolating Erwinia tracheiphila and keeping it alive in culture has been a formidable barrier to learning more about bacterial wilt ecology. A Microbiology student rotating in our lab, Xuesong Wen, recently developed a specific primer for E. tracheiphila, using a portion of the 16S region of rRNA (Phytopathology 96:S122). We plan to use this primer to detect the pathogen in extracts from cucumber beetles and cucurbit plants, in order to shed light on acquisition and transmission of E. tracheiphila by both species of cucumber beetles.

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