Phyllosticta minima is a common and widespread fungus. It occurs in eastern North America and west to the Great Plains. It causes a disease known as Purple Bordered Leaf Spot on maples. It infects mostly Amur, Japanese, red, and silver maple, but also mountain and sugar maple, and in other areas, Tartarian and sycamore maple.
The infected leaf develops small, round, tan spots with purple or brown margins. Tiny, black, pimple-like fruiting bodies form in each spot. The dead tissue in the middle of the spot sometimes breaks away, leaving a small hole.
Infections are most common in wet years and on the bottom third of the tree. Some infected leaves may eventually turn brown and drop off the tree, but most trees are able to withstand the infection. Control involves removing leaves with spots from the tree, and raking up and removing fallen leaves. That prevents further infections in the current growing season, and reduces the number of infected leaves that will overwinter.