Fungal leaf spot is seen on many ornamental plants including
Maples, and many others
It usually starts as small tan-black spots that increase in size and clumping until portions of the leaf fall out. Many leaf spot fungi have an aura around the darker center area. Leaf spot usually begins in the center of plants that have a lot of foliage where air is limited. High humidity and cool temperatures are perfect for many leaf spot fungi. Leaf spots interfere with photosynthesis which stresses plants. Fungicidal spray is the best way to control leaf spot. Spray when weather indicates the issue will be prevalent or as soon as you notice an issue. Use Fung-onil, Daconil, Copper, Sulphur, Serenade or Neem oil. Remove badly infected leaves, open the plant up for good air circulation, and avoid overhead watering of plants to control all fungi.