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.
Occasionally, lesions develop on one side of a fruit, causing it to hook as it grows. Causal Organism Gummy stem blight is caused by the fungus Didymella bryoniae. The pathogen can be seed-borne or can survive on organic debris from previously infected cucurbits or on wild or volunteer cucurbits. The gummy stem blight fungus produces two types of spores. Windblown ascospores are likely to start the disease in a field.