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Extension > Garden > Yard and Garden > Vegetables > Diseases of cucurbits > Scab

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Back to Diseases of cucurbits


Michelle Grabowski

Scab is caused by the fungus Cladosporium cucumerinum. The fungus infects cucumbers, melons, summer squash, pumpkins, and winter squash. Watermelon is very resistant to the disease and many varieties of cucumber that have resistance to scab are now available.

plant stem with distorted, discolored leaves

B. Watt, University of Maine,


Important biology

two black pumpkins with white scabs

M.Grabowski, University of Minnesota

Scab can be introduced into the field on infected seed or as spores carried on moist air currents. Fungal spores are then spread through the field by wind, insects, tools, and workers. Scab survives the winter in plant debris and once introduced, can reoccur season after season if management strategies are not implemented. Disease development is favored by cool (around 70F), moist weather.

Summer squash, pumpkins and cucumbers (varieties not specifically bred for disease resistance) are considered very susceptible to the disease. Fruit infections on these crops will profusely sporulate and rot will extend deep into the fruit.

Gourds and some winter squash (blue hubbard, buttercup) are moderately susceptible and will show symptoms on both leaves and fruit. Fruit infections, will not extend deep into the fruit however. Moderately resistant squash, like acorn and butternut, have few leaf spots and fruit infections will be raised tan corky spots instead of sunken craters. Fruit spots in these crops rarely produce fungal spores.


swollen cucumber with black spots and white fuzz

M.A. Hansen, VA Poly Tech Inst.,

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