Soil, Crop and Pest Management

Pumpkin Diseases

Robert L. Wick, Department of Plant Pathology

Fernald Hall, UMass, Amherst, MA 01003

Phytophthora Blight: Phytophthora capsici causes the most destructive blight of pumpkin in our region. Fortunately it is not the most common disease nor is it likely to blow in from any distance. It could conceivably blow across the street but the most important method of spread is with farm equipment and by water moving on the soil surface.The fungus resides in the soil and becomes a permanent resident. Disease will occur whenever susceptible plants are grown and soils become saturated. All cucurbits, tomatoes, eggplant and pepper are hosts to this pathogen. Grow non-host crops in Phytophthora-contaminated soil. Ridomil/Bravo® will provide some measure of control. Avoid transporting soil from a contaminated field to a non-contaminated field. Plow and harrow contaminated fields last. Spray soil off of farm equipment after working in contaminated fields.

Black Rot: Black rot is more widespread than Phytophthora but is usually less destructive. The pathogen overwinters on diseased plant debris but does not survive in the soil. Black rot is confined to cucurbit crops and is most important on winter squash and pumpkins. Deep plow plant debris after harvest. Rotate out of cucurbits for at least two years following black rot. Bravo 720® will provide protection if used on a regular basis.

Scab: Scab is common on pumpkin and summer squash. The disease only occurs during rainy periods when temperatures are cooler than normal. In northern New England, scab is more common and troublesome than toward the south. The fungus overwinters on plant debris. Deep plow after harvest. Rotate out of cucurbits for two years. Sunny well-drained sites are less conducive to scab development than hollows and shaded sites. Bravo 720® may help reduce scab.

Powdery Mildew: Powdery mildew occurs during periods of high humidity, usually late in the season. The damage to the leaves can reduce yield (by weight) and increase susceptibility to black rot. Destruction of the foliage may also result in sun scald with subsequent colonization by secondary fungi (post-harvest rot). Karathane® 25WP, Benlate® 50WP and Bayleton® 50WP will control powdery mildew.

Viruses: Pumpkins are susceptible to at least six viruses but we most commonly see watermelon mosaic virus (WMV-II), Papaya ringspot virus (PRSV-W) and zucchini yellows mosaic virus (ZYMV). All three viruses are spread by aphids in a non-persistent manner. This means that the virus is spread quickly and efficiently, and that insecticides will have very little affect on control. Transplants should be carefully monitored and kept free of aphids.

Post-Harvest Fruit and Handle rot: Fruit and stem rot that occurs after harvest is generally due to infection that took place in the field. Fruit rot often develops on fruit that has sun scald. Post-harvest rot and handle rot can be reduced by applying fungicides during the growing season on a regular basis, as for control of black rot, scab and powdery mildew. Fruit should be stored at 50-55 F and 70-75% relative humidity.