Powdery Mildew
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When it strikes
About
Powdery mildew is a group of fungi affecting cucurbits, grapes, roses, squash and many ornamentals. Unusually, it thrives in warm, dry conditions with high humidity but does not need leaf wetness, making it common in late summer.
Symptoms
White to grey powdery coating on the upper surface of leaves and stems, later yellowing, curling and premature leaf drop. Fruit may be stunted or sun-scorched as the canopy thins.
Organic Treatment
Spray potassium bicarbonate, sulfur, or diluted milk solution at first signs; remove the worst leaves. Neem oil and Bacillus subtilis help slow spread. Improve airflow and sun exposure.
Chemical Treatment
Myclobutanil, tebuconazole, or trifloxystrobin on a 10–14 day schedule. Rotate chemistries and avoid sulfur in hot weather or on sensitive crops.
Prevention
Plant resistant varieties, space for airflow, prune dense growth, avoid excess nitrogen, and grow in full sun. Water at the base.