Powdery Mildew on Seven Sisters Rose: Chalk-Dust Foliage

The white coating on your friend's Seven Sisters rose—top and bottom leaves, like thrown chalk dust—is powdery mildew. Unlike most fungi, it thrives in warm, dry conditions with high humidity.

Why It's Powdery Mildew

• White/gray powdery coating on all plant parts
• Not limited to leaf undersides (rules out spider mites)
• Spreads by windborne spores
• Common on older varieties like Seven Sisters

Treatment Options

Fastest: Commercial fungicide (neem oil, sulfur, or synthetic) per label.

Homemade (weekly until clear):

• 1 heaping tbsp baking soda
• 1 tbsp canola oil
• ½ tsp liquid dish soap
• 1 gallon water

Prevention for Next Year

• Full sun, good air circulation
• Water at base only
• Prune for open structure
• Resistant varieties for new plantings

Reference: Cornell Powdery Mildew Fact Sheet

Treat now—mildew weakens the plant and ruins the glorious Seven Sisters bloom display.