Leaf symptoms appear as numerous small, water-soaked or pale green spots. These spots gradually turn white to gray and become angular. Often, lesions are surrounded by a yellowish halo, and the lesion center tears away, leaving ragged holes in the leaves. On fruit, small (1/8-inch), gray, slightly sunken, oozing, gummy spots develop that resemble insect "stings". Later, the spots enlarge and finally become distinct sunken cavities. Affected fruit are often invaded later by soft-rotting bacteria that produce a mushy, foul-smelling decay. On highly resistant fruits, especially on certain squashes and pumpkins, irregular, knoblike formations may develop.
The scab fungus overwinters on the seed and in crop debris (especially squash and pumpkin). Temperatures between 59 and 77 F, accompanied by moist weather, with frequent fogs, heavy dews, and light rains, are most favorable for scab development. Under these conditions, spores are produced and spread locally by splashing rain and by equipment or workers moving through the field, or long distance by moist air currents. Secondary disease cycles can occur as long as the weather remains favorable.