Powdery mildew is one of the most common and easy-to-recognize plant diseases – you'll see powdery white or gray spots on the leaves and stems. Although it is unattractive, this fungus will rarely kill your plant. However, it does stress and weaken the plant: infected leaves can fall prematurely, buds may not open, the flavor of edibles can be diminished. Almost no plant is immune, but some of the more commonly affected are squash, cucumbers, phlox, monarda, roses and lilacs.
What Causes Powdery Mildew? Powdery mildew spores are carried to your plants by wind, insects and splashing water. Conditions that encourage powdery mildew include:
- Dampness or high humidity
- Crowded plantings
- Poor air circulation
How Can You Control Powdery Mildew?
- Choose healthy plants and keep them growing healthy.
- Try and find a powdery mildew resistant cultivar, if your area is susceptible.
- Don't plant non-resistant varieties in the shade
Once Your Plants are Infected:
- Remove and destroy all infected plant parts.
- Improve air circulation by thinning and pruning.
- Don’t fertilize until the problem is corrected – powdery mildew favors young, succulent growth.
- Don’t water plants from above.
- Apply a fungicide. Your local garden center can help you choose the most effective and safest type for your plants.