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Powdery Mildew on Magnolias: Seasonal Management in Oregon

Question: Two magnolias in western Oregon got powdery mildew after cool, wet summer. Leaves off now. Winter/spring treatment? Will it return?

Answer

Mildew thrives in humid conditions. No winter treatment needed. Start at bud-break next spring with fungicide (Banner Maxx, Immunox, sulfur, etc.), repeat monthly if conditions favor spread. Severity varies yearly with weather.

Fungicide Options

Propiconazole (Banner Maxx)
Myclobutanil (Immunox, Eagle)
Sulfur (avoid >90°F)
Triforine (Funginex)
Triadimefon (Bayleton)

Check local nursery for tree/shrub labeled product.

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