Powdery mildew can quickly decimate your flower or vegetable garden. It often begins as a greyish-white powder on the lower leaves of plants, and then quickly overtakes the foliage, flowers or fruits. Powdery mildew is unattractive at best and deadly in some cases. The mildew thrives in beds that receive little sun and too much moisture. Treat powdery mildew as soon as you notice it to prevent it from spreading to healthy plants or killing already infected plants.
Remove infected leaves from the plants. Cut off any mildewed leaves or flowers and dispose of them. Pull up and dispose of any plants that are severely infected.
Thin out the interior of large plants. Remove up to one-third of the branches with shears to allow better air circulation to the interior of the plant.
Stop any nitrogen fertiliser treatments until the powdery mildew is controlled. High nitrogen levels in the soil encourage powdery mildew to spread.
Remove any dead leaves or other garden debris from the bed and dispose of it. The dead plant matter retains moisture and provides a breeding ground for mildew spores.
Treat the plants with agricultural sulphur or a sulphur fungicide treatment available at gardening stores. Follow package instructions for exact application methods and rates. Fungicides do not cure powdery mildew but they do prevent it from spreading to the healthy parts of the plants.
Always follow the spacing and sunlight recommendations on the plant label when planting the garden. Water plants at the base and avoid wetting the foliage to help prevent powdery mildew from overtaking wet leaves.
Wash your hands and any gardening tools after every use; otherwise you may spread powdery mildew to healthy plants and beds.