Farm Progress Reports




Horticulture Station


Plant Pathology


Bacterial wilt causes major losses in organic cucurbit crops (muskmelon, cucumber) throughout Iowa and the eastern United States. Striped and spotted cucumber beetles transmit the disease. Disease-causing bacteria (Erwinia tracheiphila) survive in beetle hindguts and enter plants when their infected frass touches feeding wounds or floral nectaries. After infection, plants wilt and die within two weeks. To prevent beetles from feeding on cucurbits and spreading bacterial wilt, organic growers often cover plants with spunbond polypropylene row covers (Agribon™, Reemay®) in the first several weeks after transplanting. The row covers are suspended over low wire hoops (1.5 ft tall), and edges are secured using soil. When female flowers develop, row covers are removed to allow for pollination. From then until harvest, cucumber beetles are controlled with insecticides. Despite their widespread use, the traditional “low tunnel” systems have practical limitations. The need to remove spunbond row covers for pollination and to avoid overheating plants limits the benefits to a short window of time early in the growing season. The organic insecticides used to control beetles after removing row covers are weak and easily washed away by rain. They require frequent reapplication, costing growers precious time and money. The objective of this study is to redesign row cover systems to achieve full-season protection against bacterial wilt and minimize dependence on insecticides. A new nylon mesh row cover material (ProtekNet) and tall hoop supports (3.5 ft) made of 1-in.diameter galvanized conduit pipe were used to test two slightly different “mesotunnel” systems. The mesh holes of ProtekNet allow ventilation to prevent overheating, yet are small enough to exclude cucumber beetles. Additionally, fungicides can be sprayed through it.





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