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Phytophthora Crown and Fruit Rot in Pumpkins

Posted: August 8, 2012

Pumpkin growers throughout Pennsylvania have carefully monitored their crop for signs of powdery mildew and other diseases, but the recent heavy rainfall in some areas may spark an outbreak of Phytophthora crown and fruit rot in some of the poorer draining fields.
Phytophthora crown and fruit rot on pumpkin. Photo credit Tom Butzler.

Phytophthora crown and fruit rot on pumpkin. Photo credit Tom Butzler.

Phytophthora crown and fruit rot is caused by the oomycete, Phytophthora capsici. This organism thrives when air temperatures are between 77 and 830 F and when there is abundant rainfall to aid the swimming zoospores in their infection of susceptible plants.

In 2008, Central Pennsylvania pumpkin growers felt that they were on their way to an above average year when a series of torrential rain events fueled by tropical moisture hit the area. While none of the fields were completely flooded, growers did note standing water in some sections of their fields. Within days, growers noticed white on a few pumpkins and before a week had past the growers were watching helplessly as Phytophthora crown and fruit rot spread like a wildfire across their fields leaving a wake of rotting pumpkins and dying vines.

Growers who have pumpkins growing in poorly drained fields should consider applying a tank-mix of fixed-copper (at labeled rates) with fungicides like Revus, Presidio, Forum or Tanos when conditions favor disease development. The fungicide Ranman can also be used to suppress this disease in pumpkin fields, but it cannot be combined in a tank-mix with a fixed copper. Growers should alternate fungicides with different modes of action or Fungicide Resistance Action Committee (FRAC) codes to minimize the chances for fungicide resistance.

Fields where Phytophthora crown and fruit rot have been detected should be rotated away from susceptible crops for a minimum period of three years. Susceptible crops include tomatoes, eggplant, pepper, lima beans, snap beans, and other cucurbits.

Tom Ford, Penn State Extension, (tgf2@psu.edu)