Black rot symptoms on butternut squash fruit showing irregular ring patterns and water-soaked areas. Fruit symptoms vary among crops. Black rot symptoms appear as a brown to black rot of the rind, flesh, and seed cavity accompanied by heavy white and black fungus growth. Lesions may develop anywhere on the fruit, first as water-soaked areas dotted with pycnidia that ooze yellowish masses of spores. Seeds often become dotted with small black pycnidia.
Infection usually occurs in the field, causing water-soaked, cracked, brownish cankers on the vines.
A reddish gum may develop in these cracks, although this alone is not a diagnostic sign. Fruit may decay at the site of attachment as a result of the fungus invading the stem. Butternut squash and gourds may develop black rot before harvest, but Hubbard squash are resistant during growth and do not show symptoms until the storage period. Fruit rot on greenhouse cucumbers usually begins at the blossom end of immature fruit. Lesions are firm and become dark brown to black when cut open.