PlantLife Online

Answer

Assuming the cucumber plants are receiving adequate water and nutrients there are a number of diseases that maybe affecting your cucumbers. The species Cucurbits which include cucumbers, melons, squash, pumpkins, and watermelons are commonly affected by Bacterial wilt, anthracnose, powdery mildew, Angular leaf spot and Alternaria Blight.

Bacterial wilt is caused by the bacterium Erwinia tracheiphila. The bacteria invade the vascular tissues of cucumber and melon plants, causing a rapid wilt of the plant. Plants are infected by the stripped cucumber beetle moving from plant to plant feeding on the leaves.

Anthracnose is caused by the fungus Colletotrichum lagenarium, is a severe disease that spreads rapidly in warm, wet weather. The disease attacks all above-ground parts of cucumber, melon, and watermelon. Symptoms first appears as yellow spots on older leaves eventually turning brown.

Powdery mildew is caused by the fungus Erysiphe cichoracearum and is common on cucumber, melon, squash, pumpkin and watermelon. Powdery white spots develop on the upper surfaces of older leaves, usually beginning at mid-season or later.

Angular leaf spot is a cucumber disease caused by the bacterium Pseudomonas lachrymans. The disease produces angular water-soaked leaf spots which may appear "greasy" green. The spots are restricted by the main veins. Later, the spots turn brown, dry up, and develop ragged tears in their centers.

Alternaria blight, caused by the fungus Alternaria cucumerina, infects melon, squash, cucumber, pumpkin, and watermelon. Melons are quite susceptible and most commonly infected. Spots develop first on older leaves near the center of the hill.

The best management for these diseases is proper garden preparation, seed selection and garden cleanliness. Avoid planting Cururbits species in the same location year after year, rotating crops will avoid the build up of pathogens in the garden soil. Remove all weeds and avoid planting in locations where they are near areas with large amount of weeds near by, many weeds are known carriers of disease. Each season its also important to clean and discard all the plant waste in the fall.