Cucumber scab

Symptoms. At first, a sticky substance is exuded in drops as if the trouble were the result of an insect puncture. Spots then gradually turn gray, become slightly sunken, and enlarge to about 0.375 inch in diameter. The canker gradually grows darker, and the tissue collapses farther into the cucumber until a pronounced cavity forms, lined with a dark green, velvety layer of fruiting fungus.
The first symptom on foliage is the appearance of a slightly water-soaked, paler-green area. Spots usually are numerous. Gradually they turn gray-to-white and become angular, often with yellow margins. The fine vein in the spots may remain brown or tan and are distinct against the white background. The dead tissue cracks, breaking away until the whole leaf has a ragged appearance.