Plectosporium Blight (Microdochium
Blight) of Cucurbits
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.