Inspect the tree periodically for dying branches. Leaves partially killed appear as if scorched. The disease is more common during prolonged rain periods when it may cause severe defoliation of trees. Several applications of fungicides may be required to control the disease during periods of high humidity. Many leaf spots, one-fourth inch or more in diameter, some irregular, some with indefinite margins, occur on boxelder.
Spots have brown margins and light colored centers.
Some of the spots may develop black bodies, which are the fruiting structures of the fungi. Diseased, fallen leaves should be raked up and burned. Spraying the tree several times at two week intervals may be needed to keep the disease in check. A white to grayish mold develops on the surface of the leaves. The disease is seldom serious on boxelder.