Crimson Sentry Maple Powdery Mildew: Multiple Control Options

Karen in Zone 3-4 Canada: 5-year-old maple has severe powdery mildew on new leaves, drying up. Asks about dormant oil safety and last winter's south-side dieback.

Disease & Timing

Powdery mildew (Uncinula circinata, Phyllactinia corylea) favored by humid nights, dry days, 70-80°F. Not usually serious but ruins appearance.

Cultural Controls

• Full sun, open spacing, prune for air flow.
• Avoid night sprinkling Aug-Sept; soak soil instead.
• Clean up infected debris in fall.
• Balanced fertilizer (excess N worsens mildew).

Chemical & Home Remedies

• Fungicides: myclobutanil (Immunox), propiconazole (Banner), thiophanate-methyl (Cleary's 3336), triadimefon (Bayleton), triforine (Funginex).
• Spray at first sign, cover both leaf surfaces, repeat 7-14 days.
• Milk spray: 10-30% milk (1:9 to 3:7) weekly—90% control, also foliar feed. >30% grows harmless fungus.
• Baking soda: 5 g/L water for mildew; 3 tsp + 1 tsp fertilizer + few drops soap per gallon for roses.

Dormant oil not standard for maple powdery mildew.