Anthracnose

   Leaf spot lesions caused by the fungus, Colletotrichum orbiculare (C. lagenarium), occur on leaves, stems, and fruits, resulting in serious losses in cucumber, watermelon, and muskmelon. The disease rarely affects squash or pumpkins. Lesions are distinguished by the pinkish spore masses which develop in the lesions. The symptoms first appear on the foliage as small, yellowish water-soaked areas which later turn dark and dry out. The lesions are not restricted by the leaf veins. Severely affected vines usually die. Shallow brownish elongated lesions develop on infected stems and petioles. Circular, black, sunken cankers also appear on the fruits. Black specks appear on enlarged fruit lesions, and under humid conditions. Salmon-colored spores ooze from the black specks. Anthracnose is spread by infected seed, wind, rain, insects, and by field workers, especially during wet weather. The disease is soil-borne for over 3 years and is also carried on volunteer weedy cucurbits, such as Commelina diffusa, after harvest.

   To prevent spreading the disease by plant refuse it is important to destroy the crop immediately after the last harvest. Also, five year rotations are recommended on anthracnose infested areas. Weekly fungicide preventative programs at >100 psi are recommended during humid rainy weather in areas where anthracnose is a problem. Resistance is available in some cultivars such as Dasher II, Pixie, Poinsett 76, Slice Master, and Sprint 440 II.