Organic prevention, management of powdery mildew on plants
MUKWONAGO, WI — Spots and patches of white or gray talcum powder-like substance on a plant means powdery mildew has infected the plant. This is one of the most widespread fungal diseases and attacks a wide range of plants.
The mildew may be seen on a variety of trees, shrubs, flowers, vegetables and lawn grasses. Don’t despair, the risk of this disease can be reduced 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. People will typically see more mildew problems in crowded plantings, damp and shady locations as well as areas with poor air circulation.
Powdery mildew, like other diseases, occurs when the fungal organism and susceptible plants are present together and environmental conditions are right for the disease to occur.
Remove one of these factors and the disease can be eliminated. Nobody can change the weather but there are some things a person can do to reduce the risk of powdery mildew.
Avoid purchasing mildew susceptible plants. Instead select disease resistant varieties whenever possible. Fortunately, many new varieties of phlox, bee balm, lilacs and other mildew-resistant plants are now available at garden centers.
Further decrease the risk by growing 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. The plants will be healthier and better looking when they have space to show off their beauty.
Thin susceptible varieties of perennial plantings like phlox and bee balm in spring as new growth emerges. Removing one fourth of the stems increases light penetration and airflow reducing the risk of powdery mildew.
Grow vine crops like cucumbers and squash on trellises and fences to accomplish the same results. Support large fruits of squash and melons with cloth slings anchored to the trellis.
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 and is impacting the health and beauty of the plants, gardeners may decide to intervene. Lightweight horticultural oils trap the fungal spores on the plant preventing it from spreading.
Select OMRI certified products like Summit® Year-Round® Spray Oil (SummitResponsibleSolutions.com) 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 the success rate.
Check plant tags, purchase wisely and adjust plant maintenance to reduce powdery mildew problems in the landscape. A bit of prevention and proper care go a long way to 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. She hosts The Great Courses “How to Grow Anything” DVD series and the nationally syndicated Melinda’s Garden Moment TV & radio segments. Myers is a columnist and contributing editor for Birds & Blooms magazine and was commissioned by Summit for her expertise to write this article.
For more information, visit Myers’s web site at www.melindamyers.com.