Could be a fungal or bacterial disease.
Fungal leaf spot on maple.
If you see a random pattern of spots on the leaves of your plants you’ll want to check out the diagnostics link I have to the U of MN extension service. It’s on my Favorite Links page.
If the majority of the leaf is still green, not to worry. Remove the infected leaves, clean up the area and toss the debris. Do NOT compost it. Never remove more than one third of a plants leaves or you’ll do more harm than good. Air circulation is key to preventing fungal diseases. Mulch your plants to keep the humidity down as well.
