powdery mildew on my zuccini

Asked September 15, 2015, 6:41 PM EDT

how to get rid of it?

Deschutes County Oregon

1 Response

Powdery mildew is very common. The Pacific Northwest (PNW) Plant Disease Handbook states that this fungus has a wide host range including many vegetables and ornamentals. Powdery mildew is most prevalent under conditions of cooler temperatures and high humidity. These conditions occur with poor air circulation or when cool night temperatures follow warm day temperatures.

The best method of control is prevention. Choosing disease resistant plant varieties, locating plants in full sun, and following good cultural practices will adequately control powdery mildew in many situations. Next season you may want to plant a variety of zucchini that is less susceptible to powdery mildew. Avoid overcrowding when planting, as plants require adequate air circulation. The best time to water is mid-morning, so plants have the opportunity to dry during the day.

As we enter the end of the growing season, it is important to clean up all infected plant debris, and dispose of it in the garbage. Do not put infected plant debris into the compost pile. Rotate where you plant squash family plants from year to year (a 2 year rotation is good).

For most effective results, it is recommended that protectant fungicides be applied to susceptible plants before (early spring) or in the earliest stages of disease development. Once mildew growth is mild to moderate, it generally is too late for effective control with protectant fungicides. Chemical controls can vary for specific plants. For additional information about chemical controls for home use, please call the Master Gardener Plant Clinic at the Deschutes County OSU Extension Service in Redmond: 541-548-6088.