Powdery mildew often appears as pale, flour-like patches on squash leaves before the plant declines. Early recognition lets you improve airflow and remove badly affected material while avoiding confusion with dust, residue, or natural leaf markings.
Inspect the pattern
Look for white or gray patches on the upper surfaces and, sometimes, the undersides of leaves. Check whether the growth wipes away as loose dust or remains as a spreading patch. Examine new leaves and nearby plants because the disease can move through a crowded bed.
Improve the growing conditions
Thin crowded foliage only as needed and keep weeds from closing the air space around the plant. Water at the soil line in the morning and avoid repeatedly wetting leaves late in the day. Do not overfertilize with nitrogen, which encourages dense tender growth.
Remove and monitor
Prune the worst affected leaves with clean tools and place them in the trash rather than compost if disease is active. Do not strip the plant bare; it still needs healthy leaves to produce food. Check every few days for new patches and signs of stress.
Use treatments carefully
If a labeled treatment is appropriate for edible crops, follow its label, harvest interval, and application directions exactly. Test a small area first and avoid spraying during heat or when pollinators are active. Severe recurring mildew may require a resistant variety and better spacing next season.