This disease is caused by a fungus that infects the leaves of cucumbers, melons, pumpkins, and squash.
Infected leaves develop roughly circular, yellowed spots on the upper leaf surface.
These spots later turn brown and eventually cover the entire leaf. Whitish or purplish spore masses often can be seen on the underside of infected leaves. Older leaves near the center of the vine are infected first and the disease spreads outward. Avoid wetting the leaves when watering. Plant resistant varieties.