Organic Prevention and Management of Powdery Mildew on Plants

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By Melinda Myers

Spots and patches of a white or gray talcum powder-like substance on your plants mean powdery mildew has infected them. This is one of the most widespread fungal diseases, and it attacks a wide range of
plants. You can reduce the risk of this disease with proper plant selection, maintenance and, if needed, organic intervention.

Powdery mildew is most common during hot dry weather. Wet foliage does not increase the risk of this disease, but high humidity does. You’ll typically see more mildew problems in crowded plantings and damp and shady locations as well as areas with poor air circulation.

Avoid purchasing mildew susceptible plants. Select diseaseresistant varieties whenever possible. Many new varieties of phlox, bee balm, lilacs and other mildew-resistant plants are now available.

Grow plants at the recommended spacing in the preferred amount of sunlight. Giving plants room to reach full size ensures they will receive sufficient sunlight and air circulation, thus reducing the risk of this and other diseases.

Avoid excessive nitrogen fertilization that encourages lush succulent growth that is more susceptible to this and other diseases and many insect problems. Consider using low-nitrogen, slow-release fertilizers that promote slow steady growth above and below ground.

If mildew continues to be a problem, lightweight horticultural oils trap the fungal spores on the plant preventing it from spreading. Select Organic Materials Review Institute (OMRI) certified products like Summit® Year-Round® Spray Oil ( that are approved for
organic gardeners.

Always read and follow label directions of all chemicals, organic or synthetic, before applying to any plant. Thorough coverage of the upper and lower leaf surfaces and stems will improve your success rate.

Check plant tags, purchase wisely and adjust plant maintenance to reduce powdery mildew problems in your landscape. A bit of prevention and proper care go a long way in reducing the time spent maintaining healthy, productive and beautiful gardens and landscapes.

Melinda Myers ( has written more than 20 gardening books, including Small Space Gardening.


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