The Q&A Archives: White powdery leaves and stems

Question: What is the white powdery stuff that is on the leaves and stems of my Rose of Sharon Plants.

Answer: What you describe sounds like a fungal disease called powdery mildew. To reduce additional infections, avoid overhead watering to help reduce the relative humidity. Remove and destroy all infected plant parts (leaves, etc.). Selectively prune overcrowded plant material to help increase air circulation. This helps reduce relative humidity and infection. If cultural controls fail to prevent disease buildup, or if the disease pressure is too great, an application of a fungicide may be necessary. 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 rose of sharon.

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