Controlling Powdery Mildew
Powdery mildew has been spotted at the garden. Here are some tips and advice for controlling the disease.
Powdery mildew is a group of diseases caused by several closely related species of fungi, and appears as white or gray powdery patches or film on the leaves and stems of plants.
While Powdery mildew is not usually fatal to the plant, it does injure the leaves infected with the fungus, which can result in leaf drop and, in turn, reduces nutrient to the plants and cause a general decline of the growth and vigor. The fungal spores overwinter on plants and in plant debris and are spread by wind and sucking insects.
The best control of powdery mildew is prevention by cultural control, which includes the following:
Treatment may prevent infection or slow a new infection, but will generally not “cure” an infection.
Products on the market
Ingredients in products on the market that are useful in control of powdery mildew (and some other fungal diseases) and are approved for use in organic gardens include the following:
Check for products with these ingredients and the OMRI listing (which documents its acceptance for use under the National Organic Program). Read the label thoroughly before using (the label is the law)!
There are some home-based remedies that are said to be effective in preventing or controlling powdery mildew, although much of the “proof” of this is anecdotal.
One such home remedy is a solution of baking soda (sodium bicarbonate; 1 tablespoon), vegetable oil (2 tablespoons) and castile soap (one-half teaspoon) mixed in a gallon of water, which is then thoroughly sprayed on upper and lower sides of leaves.
Another is a milk solution (1:10 dilution with water), similarly sprayed thoroughly on the plant leaves. Both of these approaches require weekly (or so) spraying and after each rain. Lots of information on powdery mildew is available through web searches; once such resource is here: https://www.mastergardeners.org/publications/powderyMildew.html.