Peony Powdery Mildew: Organic Home Remedy (Cornell Formula)

6 peony bushes with powdery mildew. Sprinkler waters every other day. Read about Messenger, Serenade, cutting back. What's best?

Organic Treatment: Cornell Baking Soda Formula

Mix: 1 tbsp baking soda + 1 tbsp light horticultural oil (or cooking oil) in 1 gallon water. Shake well.

Application

• Spray to runoff every 4–5 days
• Contact killer—must coat mildew
• Continue as long as needed
• Fall: Cut all stems to ground, remove debris
• Next spring: Preventive spray on new growth

Why This Works

• Baking soda alters leaf pH → inhibits fungal germination
• Oil improves coverage and adhesion
• Safe, cheap, effective for powdery mildew

Cultural Fixes

• Switch to drip irrigation (wet leaves = mildew)
• Space plants for air flow
• Full sun