White, powdery fungal growth which develops on the top surface of the leaf, can be seen on new shoots and buds and sometimes envelop the entire plant. A common fungal problem that affects a wide variety of greenhouse and outdoor crops. Powdery mildew can be a major problem of roses, often encouraged by plants growing in dry soils and by humid or damp air around the top growth of the rose. Roses are commonly affected but if treated early enough can usually be controlled quite effectively.
Product solution: Systhane Fungus Fighter, Fungus Fighter Disease Control, Multirose Concentrate 2, Multirose 2 Ready To Use. Use preventatively before any signs of powdery mildew are evident.
Cultural measures: Ensure that plants are kept well watered in dry spells and are not overfed. Remove infected plant debris and leaves. Try watering in the evening as this is a better time to water plants as evapouration rates will be reduced.
Consider growing rose varieties that offer some resistance to powdery mildew.