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Sounds like powdery mildew. Powdery mildew fungi spread quickest when the humidity is high and temperatures are between 50F and 90F. To discourage the disease, plant on sites with good air drainage, give the plants plenty of space, water during the morning only, and allow the soil to dry out between waterings. Remove any affected leaves, and if your plant is heavily covered with powdery mildew you should probably remove the entire plant so the infection doesn't spread. For heavy infestations of powdery mildew, sulfur or copper sprays can be applied weekly, starting in June in your area. These include: sulfur, neem oil (Rose Defense, Shield-All, Triact), triforine (Ortho Funginex), or potassium bicarbonate (Kaligreen, First Step) Chemicals are most effective when combined with cultural controls. Best wishes with your landscape! |
