How to spot it

White or gray powdery spots on leaves and stems that spread until the leaves look dusted with flour.

What it does

Leaves yellow, brown, and die early, so fruit ripens poorly and tastes bland. Common from midsummer on. Unlike most leaf diseases, it doesn't need wet leaves.

What to do now

• Remove the worst leaves.
• At the first spots, spray potassium bicarbonate, sulfur, or neem oil, and repeat weekly. Don't use sulfur above 90°F or within 2 weeks of an oil spray.

Keep it away next time

• Grow resistant varieties ("PM" or "PMR" on the seed packet).
• Give plants sun and room for air to move.
• Sow a second planting of squash and cucumbers in midsummer to take over from tired vines.

Helpful supplies

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Plants it affects

Every plant in the squash family (cucurbits).

See also