Black rot of winter squash, pumpkins, and gourds is caused by the fungus Mycosphaerella melonis . Circular, black or tan spots appear on the cotyledons and stems of young plants. Seedlings can be killed and plants that escape early damage can develop lesions on stems near the center of the hill. Cankered vines eventually wilt after midseason. On the fruit, the disease appears first as a brown rot of the rind, flesh, and seed cavity often accompanied by a white and black growth of mold.
Sclerotinia is a common cause of storage rot in Hubbard squash.
This problem is most severe where beans or cabbage have grown recently in the rotation since this fungus attacks all three crops. The decay is watery and odorless, and is accompanied by a snow-white cottony mold. Black bodies the size of soybeans, embedded in the mold, serve as the overwintering stage. The fungus spreads from fruit to fruit contact in storage. Foliage becomes infected during the growing season.