ManagementĪn integrated disease management program using several disease management methods should be used to manage downy mildew in cucurbits. The timing of spore arrival each year often varies by prevailing weather patterns.ĭisease development is favored by moderate temperatures, and moisture is required for infection. In these areas, pathogen spores are introduced each year on air currents from warmer areas. The cucurbit downy mildew pathogen requires a living host to survive and does not overwinter in areas where freezing temperatures prevent cucurbit production in the field. This means that, in a given area, downy mildew may develop on one or more cucurbit hosts but may not develop on others. Each pathotype differs in which cucurbit host or hosts it can infect. Several pathotypes (subdivisions) of the pathogen exist. This pathogen is a member of a group of fungal-like organisms (oomycetes) commonly referred to as water molds. Pathogen and Disease Spreadĭowny mildew in cucurbits is caused by the pathogen Pseudoperonospora cubensis. Magnified view of leaf hairs and pathogen spores (sign) on the lower surface of a squash leaf. Gray- to purple-colored pathogen growth (sign) on the lower surface of a squash leaf. Under favorable environmental conditions, the pathogen may produce gray- to purple-colored structures on the lower surface of leaves ( Figures 5 and 6) below the yellow lesions present on the upper surface of leaves. The lesions may expand to cover much of the leaf surface, eventually resulting in the death of the entire leaf. In most cucurbits, lesions have irregular margins ( Figures 1, 2, and 3) however, in cucumbers, lesions are angular ( Figure 4). Lesions may remain yellow or may turn brown. Symptoms appear between 3 and 12 days after infection and begin as slightly yellow to bright yellow lesions on the upper leaf surface. Signs and symptoms of downy mildew typically occur only on leaves. In Mississippi, this disease has been more of a problem in the fall than in the spring. This disease, sometimes referred to as cucurbit downy mildew, is known to infect more than 40 cucurbit species, including cantaloupe, cucumber, pumpkin, squash, and watermelon. Downy mildew is a potentially devastating disease of cucurbit crops that can cause significant yield losses.
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