Biology
Powdery mildew is a common fungal disease of squash. Upper and lower leaf surfaces and stems are typically affected. Small, white spots quickly enlarge into patches of characteristic powdery-white fungal growth. Older leaves, shaded leaves, and leaf undersides are favored locations for powdery mildew development, although it can quickly spread to involve large portions of the plant. Tiny, speck-like, black fungal structures may be present in the white mats. Severely affected leaves may yellow and die prematurely. Occasional fruit infections occur on cucumber, although most commercially-grown varieties are resistant. Disease development is favored by humid weather, cool nights, and cloudy days. Dense plantings are more likely to be affected.
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