Powdery Mildew: Prevention, Hydrogen Peroxide Remedy & Host-Specific Strains

Powdery mildew, a true fungus, coats leaves/flowers/fruit with white/gray powder in high humidity. Host-specific strains: rose mildew won't infect lilacs. Prevention: healthy plants, prune deadwood, space for airflow, avoid damp shade, no evening sprinklers. Organic treatment: 9:1 water:hydrogen peroxide spray weekly. Don't compost infected parts. Some plants (lilac) tolerate it cosmetically.

Prevention Checklist

• Start with vigorous plants.
• Prune dead material at proper time.
• Don't overcrowd—airflow is critical.
• Avoid damp, shady sites.
• No evening overhead water (wet leaves overnight = mildew highway).

Organic Treatment

• 9 parts water : 1 part hydrogen peroxide (3% solution). Spray thoroughly weekly.
• Sulfur, potassium bicarbonate, neem oil also effective.
• Don't compost infected debris.

Host Specificity

Each powdery mildew species infects a narrow host range. Rose mildew → roses only. Lilac mildew → lilacs only. This limits spread in diverse plantings.

Powdery mildew is a humidity disease. Proper moisture management, annual pruning, and early organic sprays keep it cosmetic. Neglect airflow, and the powder takes over.