P&PDL Picture of the Week for
August 9, 2010

Powdery Mildew of Pumpkin

Dan Egel, Extension Plant Pathologist Southwest Purdue Agricultural Center, Vincennes, IN 

Figure 2 shown here is a common sight on pumpkins in August. These pumpkin leaves are infected with a disease known as powdery mildew.  More about this disease in a moment.

The pumpkin leaves in Figure 1 are healthy pumpkin leaves with a variegated or mottled pattern. The variegated pattern runs along the veins in a regular pattern with each leaf. Note the difference between the random occurrence of the symptoms of powdery mildew in the lower photograph and the regular pattern of variegation in the healthy pumpkin leaves in the upper photograph. As a general rule, symptoms of a plant disease appear on a leaf in a random fashion. 

Powdery mildew diseases occur on a wide variety of plants. However, there are many different types of powdery mildew fungi. The fungus that causes powdery mildew on pumpkin, for example, will not cause powdery mildew on lilac.   

A little powdery mildew on pumpkin leaves will probably not matter to most homeowners. However, if the disease becomes severe, the yield and quality of the pumpkins may be reduced. Some pumpkin varieties have partial resistance to powdery mildew. The serious gardener may decide to apply fungicides to control this disease. Check your favorite garden center for products that are effective against powdery mildew and are labeled for pumpkin. 

Commercial pumpkin growers can refer to the Midwest Vegetable Production Guide for Commercial Growers 2010.

Click image to enlarge

Variegated pumpkin leaves

Figure 1. Variegated pumpkin leaves

Powdery mildew on pumpkin

Figure 2. Powdery mildew on pumpkin leaves

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service