Pumpkin Diseases

Melanie Lewis Ivey, Hadziabdic, Denita, Hollier, Clayton A., Ferrin, Donald M., Overstreet, Charles

Plectosporium blight (syn. Microdochium blight). On fruit the white lesions are more circular and less diamond-shaped than on leaves. Individual lesions often coalesce to form white to tan roughened areas on the upper fruit surface.

Zucchini yellow mosaic on pumpkin caused by zucchini yellow mosaic virus (ZYMV). Symptoms include severe knobbing that results in deformation of the fruit. General plant stunting, necrosis and the reduction in the size of leaf lamina can be observed as well.

Zucchini yellow mosaic on pumpkin. Note the severe knobbing and entirely deformed and distorted fruit. The virus damage can significantly reduce fruit marketability.

Early stages of downy mildew on pumpkin. Initially, lesions are visible as irregular chlorotic spots. As disease progresses and the lesions expand, the centers of the lesions become necrotic.

When Pseudoperonospora cubensis, the cause of downy mildew of pumpkins and other cucurbits, sporulates on the lower surface of infected leaves, it may be seen as gray to black downy growth.

Sclerotium rolfsii, the casue of souhtern blight on a wide range of hosts, causes a fruit rot of pumpkins that are in contact with soil infested with the pathogen. As the white, cottony mycleium develops, small brown sclerotia are formed. These sclerotia persist in the soil and serve as inoculum for the next susceptible crop.

Gummy stem blight is a common disease of all major cucurbits. It is caused by two fungi, Didymella bryoniae (sexual stage) and Phoma cucurbitacearum (asexual stage). The pathogen is most common in the southern United States. Cankered vines usually wilt after mid-season.

Stem cankers caused by gummy stem blight develop in the cortical tissue. Note brown, gummy exudate produced on the stem surface. Image courtesy of B. D. Bruton.

Foliar lesion of gummy stem blight. Note the presence of pycnidia (flask-shaped asexual fungal structures containing spores) in the center of lesion. Additionally, early powdery mildew colonies can be observed. Image courtesy of T. A. Zitter.

Black rot causes softening of the pumpkin rind. Gummy stem blight refers to the foliar and stem-infecting phase of the disease, and black rot to the fruit rot phase. Small, water-soaked spots containing black fruiting bodies that develop on infected fruit eventually enlarge and exude gummy material. Image courtesy of T. A. Zitter.

6/13/2005 6:37:55 PM
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