Septoria Spot in Curcubits

Septoria spot, caused by the fungus Septoria cucurbitacearum, can be an important disease of certain cucurbits. The fungus can infect the leaves of muskmelon, pumpkin, summer and winter squash (butternut, acorn, and processing “pumpkins” [actually squash]), and gourds and the fruit of pumpkin, butternut, acorn, and processing “pumpkins.” Although affected fruit are unlikely to rot in storage or to cause other fruit to rot, they may be unmarketable because of the raised white spots caused by the disease. Symptoms of Septoria leaf spot are similar on all the cucurbits infected. The spots are very apparent on muskmelon and butternut squash leaves, but are also identifiable on other cucurbits. Spots are normally circular or occasionally irregular, beige to nearly white in color, measuring 1 to 2 mm in diameter or occasionally larger on the upper leaf surface. A narrow brown border surrounds the spot and, with age, the lesion may crack.