The fungus severely affects melons and watermelons. Cucumbers, pumpkin and squash are also affected by this disease, although less severely. Leaves are usually affected. Fruits are rarely affected, although it does cause a fruit rot on some species. The disease is favored by wet, warm weather.
Oldest leaves show symptoms first.
There are usually many spots on each leaf. These spots may grow together. As the spots enlarge on muskmelon and watermelon, they develop definite, concentric rings that are visible only on the upper leaf surface, giving the spot a target-like appearance. On the lower surface, the rings are not visible and the edges of the spots are indistinct. Heavily infected leaves of muskmelon may curl at the margins, giving the leaf a cupped appearance, and the leaf may shrivel within a few days.