Wet Weather Foes
Warm damp weather has caused a surge in powdery mildew in the last few weeks. Many different strains of powdery mildew attack a wide range of host plants, including flowers, shrubs, trees, and vegetables.
Powdery mildew is relatively easy to diagnose in most plants. It typically shows as a slightly granular white or very light grey coating on the upper surface of leaves, stems, or flower buds. On a few plants, such as evergreen azaleas, it can show as very contorted foliage, with the powdery residue on the inside of the curled leaf. Be careful not to mistake powdery mildew for the natural coloration of some plants, such as summer squash and lungwort. Also, be aware that grey mold (botrytis) is somewhat similar, but harder to control. Grey mold is typically more raised above the plant surface, tends to appear on stem/crown and bud, and is distinctly grey rather than white. If in doubt, we are happy to diagnose samples you bring in to the nursery.
Prevent powdery mildew by maintaining good plant health through good planting, watering, and feeding. Unlike most fungal diseases, powdery mildew is deterred by overhead watering, and extensive reliance on drip watering often makes it worse. Keep dead leaves and spent flowers cleaned off plant and ground to reduce sources of infection.
Powdery mildew is usually quite responsive to most fungicides. We usually prefer organic treatments, such as Serenade, sulfur, copper, or neem. Combine these treatments with removal of heavily infected tissues where possible.
-Darren Morgan
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