Two tar spot diseases affect both sugar and red maple trees. One, the black tar spot caused by Rhytisma acerinum, produces large and raised black patches of fungus growth (stroma) on the upper leaf surface (Fig. 80). The other, called speckled tar spot (R. punctatum), is characterized by clusters of individual small black stromata (Fig. 81). Black tar spot is conspicuous because the black, somewhat shiny, stromata are surrounded by yellow-orange zones (Fig. 80). Infection occurs during periods of high humidity shortly after leaves reach full size. Light green and then yellow-green areas appear on the leaf surface. The black stromata form later in the season. The underside of the leaf below a black tar spot turns brown, whereas the underside of a speckled tar spot remains yellow.