Powdery mildew is a fungus which spreads a white or ash-grey film over the upper and lower surfaces of the leaves of plants - usually the older leaves. Powdery mildew fungus favours high humidity and dry conditions. Water splash and air currents spread the spores of powdery mildew which grows on the surface of the leaf only
Appearance of a whitish film on leaves and buds. New growth is distorted and older leaves become blackened. Flower buds may fail to open.