Plectosporium Blight (Microdochium Blight) of Cucurbits

M. Babadoost

Plectosporium blight (Microdochium blight) of pumpkin, caused by the fungus Microdochium tabacinum, was first reported in Tennessee in 1988. It was subsequently reported from New Jersey, Pennsylvania, Louisiana, Maryland, Virginia, and Indiana. In 2000, Plectosporium blight was observed in jack-o-lantern pumpkin fields throughout Illinois. In some fields, yield losses to Plectosporium blight were estimated to be more than 50%. It was the first report of Plectosporium blight in Illinois. In 2001 and 2002, Plectosporium blight was observed in few pumpkin fields, and with low incidence.

The most susceptible cucurbits to Plectosporium blight are pumpkins, yellow squashes, and zucchini squashes. All parts of the pumpkin plant may be affected. Spindle-shaped, tan to white lesions develop on stems, leaf veins, petioles, and peduncles. Stem and petiole lesions can result in the death of attached leaves, and defoliation can occur in severe infection. Infected stems are dry and brittle. On fruit, the fungus causes white, tan, or silver russeting. Individual lesions are less than 1/4 inch long, but often coalesce to form a continuous dry, scabby surface.

The fungus produces cylindrical or slightly curved, two-celled conidia on pumpkins and squashes. The pathogen survives in crop residue in soil. Warm, wet weather favors disease development.

No resistant pumpkin variety has been reported. Rotation with noncucurbit crops should help reduce disease incidence. The disease is readily controlled by application of protectant fungicides such as chlorothalonil (Bravo) and Mancozeb and a strobilurin fungicide Cabrio EG with though coverage of foliage and fruit.