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Gummy stem blight and black rot

Michelle Grabowski

Gummy stem blight and black rot are both caused by the fungus Didymella bryoniae. Gummy stem blight describes the leaf and stem infection stages of the disease. Black rot describes the fruit rot stage. Fruit rot may develop in the field or after the plant has been harvested.

close up of leaf with brown, dead edges

Clemson University,


Important biology

close up of stem with black spot

Clemson University,

The fungus, D. bryoniae, enters through wounds. Plants that are infested with cucumber beetles, aphids and powdery mildew have higher incidences of black rot and gummy stem blight than pest free plants due to minor wounding caused by these pests.

The black rot fungus can be brought into the field in infected seed and survives from season to season in crop debris. New spores are produced in spring in response to wet weather. Spores are then easily spread throughout the field on splashing water. Moisture on the leaves and high humidity favor disease.

three squash with red splotches

S. Jensen, Cornell University,


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