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Extension > Garden > Yard and Garden > Vegetables > Diseases of cucurbits > White mold

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White mold

Michelle Grabowski

White mold is caused by the fungus Sclerotinia sclerotiorum. This pathogen infects a wide variety of vegetable crops including beans, carrots, tomato, cabbage, and lettuce. In the cucurbit family pumpkins and some varieties of winter squash are most severely affected by the disease. This disease does not cause leaf spots but infects both stems and fruit.

fruit with large white growths

W. Brown, Colorado State University


Important biology

The white mold fungus form hard black resting structures (about the size of a raisin or smaller in cucurbits) called sclerotia that allow them to survive in the soil and plant debris for 5 or more years. These sclerotia produce small mushroom-like apothecia that release spores under cool wet weather conditions.

stems with brown patch next to ruler

P. Bachi, University of Kentucky,

White mold frequently infects pumpkin through the blossom end of the fruit, especially when the blossom remains attached after pollination. Stem infections often start where cotyledons are fading or where the plant has been wounded.


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