Extension > Garden > Yard and Garden > Vegetables >Diseases of cucurbits > White mold
White mold
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W. Brown, Colorado State University Bugwood.org
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.
Identification
- Infected fruit and stems first appear water soaked.
- Fluffy white cottony fungal growth is commonly seen on infected areas.
- Small hard, black raisin-like fungal structures, known as sclerotia, eventually develop; embedded in the cottony mold.
- Fruit are often infected through the blossom end and become rotted and watery. Sclerotia may be found inside these rotted fruit.
- Rot may occur in the field or post harvest
Important biology
P. Bachi, University of Kentucky, Bugwood.org
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.
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.
Management
- No resistant varieties are available, but plants with an open growth habit have less disease than plants with dense leaf coverage.
- Use wide row spacing, control weeds and plant rows parallel to prevailing wind to promote rapid drying of plant leaves.
- If only a few plants are infected remove them from the field before sclerotia form and bury them deeply.
- Do not compost infected fruit or other plant material.
- Crop rotation to corn or other grasses to limit or reduce pathogen in the soil.
