Powdery mildew is caused by one of the most common and widely distributed fungi that plague gardens. The disease can attack a wide range of plants, as it is caused by several species of the order Erysiphales. A sampling of commonly affected plants includes:
- Cucumbers.
- Pumpkins.
- Squash.
- Melons.
- Grapes.
- Phlox.
- Peonies.
- Lilacs.
- Bluegrass.
- Fescue.
The fungus arrives on the scene in the form of spores carried by the wind. It takes up residence in cool, shady areas and places where air does not circulate, and thrives on the soft plant tissues promoted by nitrogen fertilizer. It overwinters in dormant grass.
Symptoms
- Poor plant vigor.
- Stunted plants.
- White or grayish powdery substance on leaves.
- Deformed, shriveled, or dead leaves, shoots, vines, and flower buds.
- Sunburn on fruits.
- Small, discolored fruits.
- Prematurely ripened fruit with poor flavor and texture.
Treatment
Annual vegetables, fruits, and ornamental plants suffering from powdery mildew should ideally be destroyed to prevent the further spread of the disease. However, if you want to make an attempt to save them, you may have success with a bit of pruning and one of these fungicides:
- Sulfur.
- Raw milk.
- Baking soda.
- Hydrogen peroxide.
Organic mildew treatments are also available. Note that any fungicides must be applied as soon as symptoms first appear to be effective.
The treatments listed above will work for perennials, as well. They can be used on lawns, but this is rarely worth the cost. Most lawns will eventually recover on their own as long as they are not stressed.
Prevention
Site your garden in a place where the plants will receive sunlight and air circulation most of the day. If you do plant grass, flowers, or shrubs in a shady location, choose only varieties that prefer those types of conditions.
To ensure that light and air can penetrate the plants:
- Make sure greenhouses and tunnels are well ventilated.
- Prune plants appropriately for the species.
- Remove all dead plant matter on a regular basis.
- Control weeds.
Keep your plants healthy and stress-free to further reduce the risk of disease. Make sure their nutrient needs are met, but be conservative with fast-release nitrogen. In the case of lawns, do not weaken plants by mowing too low.
Finally, avoid wetting foliage when watering the garden. Water on the leaves tends to promote fungal growth.
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