I have a 5-6 year old Japanese maple in a pot and it's developing black spots on the new growth. Initially I thought it got too much sun when we went rapidly from a rainy spring to hot summer days but it has spread from just some brown at the edges of leaves. Any recommendations on what the issue is and how to treat it?

It looks like what my neighbor's maple tree gets every year... Maple Tar Spot fungus. It's a 50+ year old tree though, so it can't really be sprayed. It's recommended to thoroughly rake up all leaves in the fall and dispose of them, otherwise it overwinters in the leaves and hits the tree every year. I had older neighbors in the past who left them to decompose on the lawn, so it was back every year. New owners though last summer, they did rake up everything, and so far it looks much better this season, but can't really tell until fall when the leaves start coming down.

I think you can spray for it if it's a smaller tree. It doesn't really harm the tree, just a cosmetic thing, but still you want it gone.

There's more info here:
https://mortonarb.org/plant-an...