Powdery mildew is a common fungal disease that affects roses and many other plants. It is caused by fungi in the Podosphaera genus, most commonly Podosphaera pannosa in roses.
Symptoms:
- White or grayish powdery coating on leaves, stems, and buds
- New leaves may curl or twist
- Infected flower buds may fail to open or appear deformed
Common in warm, dry days followed by cool, damp nights.
Conditions That Favor It:
- Poor air circulation
- High humidity
- Overhead watering
- Shaded or crowded plantings
Cultural / Biological Control
Avoid excess nitrogen fertilizer, which promotes tender growth
Avoid watering in the evening.
Keep the rose bed clean of fallen leaves and debris.
Mulch to prevent splashing spores.
Prune affected areas and dispose of them (do not compost!).
Water at the base of the plant, not on leaves.
Organic Treatment
Organic
Neem Oil: Acts as a fungicide and insecticide. Apply according to the label instructions.
Chemical Control
Rotate fungicides to prevent resistance.
Sulfur-based fungicides (avoid in very hot weather).
Use fungicides labeled for powdery mildew on roses.
Prevention Tips
Baking Soda Spray: Mix 1 tablespoon of baking soda + 1 teaspoon of dish soap in 1 gallon of water. Spray every 7–10 days.
Choose resistant rose varieties.
Improve air circulation by spacing and pruning plants.
Milk Spray: Mix 1 part milk with 2 parts water and spray weekly. Helps prevent spread.