Scab

 

        The fungus Cladosporium cucumerinum affects all above parts of the plant and produces the characteristic scab-like lesions on the fruit. During humid weather a fungal brownish mat of spores develops on the fruit. Most yield losses are caused by infections of the fruit. It attacks muskmelon, pumpkin, and squash, but is most serious on cucumbers. Initial leaf symptoms include numerous angular, pale-green, water soaked lesions. The lesions turn brown with necrotic margins and then turn gray or white. Petioles and stems also develop elongated disease lesions and internode length is often reduced. Disease spores are transmitted by wind, insects, and by field workers and machinery. It survives in the field on cucurbit plant refuse. Conditions conducive to disease outbreaks are cool and humid weather. The disease may be controlled with periodic fungicide sprays and by planting resistant cultivars such as Dasher II, Calypso, Gemini 7 Marketmore 76, Poinsett 76, Slice Master, and Sprint 440 II. Scab resistance in cucumber is by a single dominant gene.