4 (1 = rare 5 = annual)

5 (1 = very little damage 5 = plants killed)

Powdery mildew, caused primarily by the fungus Erysiphe cichoracearum, may attack all vine crops and other vegetables. The cucurbitcrops most commonly affected are cucumber, gourd, muskmelon (cantaloupe), pumpkin, and squash.

Vegetable

• Beans (Phaseolus vulgaris, P. lunatus)
• Cucumber (Cucumis sativas)
• Pumpkin (Cucurbita pepo; C. maxima; C. moschata; C. mixta)
• Summer Squash (Cucurbita pepo and Cucurbita maxima)

Powdery mildew first appears around midsummer in the fields in Illinois. The disease can develop in greenhouse at any time. All foliar tissues can be infected. Major symptom is small, circular, talcum-like spots on vines and leaves that gradually expand and may coalesce superficial, powdery, white to gray fungal growth develop that later covers part or all of the upper leaf surface, petioles, and stems. This growth also may appear on the underleaf surface and uncommonly on the fruit. Severely infected leaves gradually turn yellow, then wither, die, and finally become dry and brittle. Premature loss of the foliage results in yield losses and poor fruit quality.

In Illinois, the fungus is presumed to overwinter in crop and weed refuse. More important sources of infection may be spores produced on greenhouse-grown vine crops and perennial hosts grown in the field in frost-free areas of the far South during the winter. These spores are believed to be blown progressively northward during the spring and early summer. The powdery mildew fungus is a bit of an oddball as far as fungal diseases go because its development is limitedby wet leaf surfaces. However, high relative humidity and temperatures around 80 F favor disease development. The fungus can reproduce and infect with a relative humidity as low as 46 percent.

Whenever possible, plant varieties that are resistant or tolerant to powdery mildew. Plant breeders have successfully bred varieties of muskmelon resistant to powdery mildew, only to have new races of the fungus develop that are capable of producing disease on these new varieties. In terms of breeding efforts, it is an ongoing battle to keep ahead of the pathogen. Where justified, apply a recommended fungicide, starting when powdery mildew is first seen incide the canopy.

Home, Yard & Garden Pest Guide
The Home, Yard & Garden Pest Guide (C1391) provides is written for homeowners and other residents and provides nonchemical and current chemical recommendations for controlling pests associated with trees, shrubs, turf, flowers, groundcovers, vegetables, fruit, and houses. In addition, you'll find detailed information about integrated pest management, pesticide safety, and pesticide application and calibration techniques. This publication may be purchased at your local University of Illinois Extension Unit office, or by calling 800-345-6087, or by placing an order online (search for "C1391").
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U of IL - Distance Diagnosis through Digital Imaging
A free plant, weed, insect and disease identification service available through your local University of Illinois Extension office. Center Educators or State Specialists review & respond to information and digital images submitted by local Extension office personnel. Some samples may require further examination or culture work (nominal fee involved) at the U of IL Plant Clinic.
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U of IL - Plant Clinic
Services include plant and insect identification, diagnosis of disease, insect, weed and chemical injury (chemical injury on field crops only), nematode assays, and help with nutrient related problems, as well as recommendations involving these diagnoses. Microscopic examinations, laboratory culturing, virus assays, and nematode assays are some of the techniques used in the clinic.
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