Dusty white or grey spots on the leaves, stems, flowers or fruit of plants and shrubs is caused by fungus. If left untreated it easily spreads to become a thin, white powdery coating on the entire plant. Young foliage and shoots are the most susceptible to excessive powdery fungal growth. Early signs of the disease are leaf curling and twisting. Powder mold does not kill the plant but will hasten its defoliation, prevent normal flowering and cause early dormancy. It is common on all types of ornamental plants and flowers. Lack of adequate air circulation contributes to the development of powdery mildew. Vinegar is an effective home remedy for the problem.
Pour 2 tbsp. undiluted vinegar into the spray bottle container. Hand-held plastic sprayers are easy to use for household plants and hose-end sprayers work well for larger outdoor areas. Use one part vinegar to 20 parts water in any size container.
Shake or stir the water-vinegar mixture and begin to spray. Cover all parts of the plant, especially the underside of leaves. Vinegar is a contact fungicide that is effective only when fungi spores are sprayed directly.
Repeat the application weekly until the powdery mold is gone. Continue to monitor plants for small round dots of white or gray fuzzy growth, which indicates a re-emergence of the fungus.