Hello John,

Thank you for your question.

We are getting a lot of questions that are related to the hot, humid, and drought-like conditions we have been experiencing, and I suspect that your tree is being affected by those conditions. In addition, I think your tree might be experiencing a fungal disease, which is typically exacerbated by our current weather conditions.

Here are some websites that I hope will be helpful. Your photos seem to match those in the first website which explains a fungus known as Phyllosticta or purple-bordered-leaf-spot. If this is what is affecting your tree, the good news is that it is mainly cosmetic and not fatal. The fact that you planted the tree in the spring may mean the fungus was in the soil from the nursery. It may also be that there are other sources in the neighborhood and the fungus arrived on the air, as fungal spores are known to do.

You may want to apply a fungicide. Be sure to follow directions. Other suggestions include paying close attention to watering and making sure to clean up any debris beneath the tree. Be sure not to compost the debris.

https://worldofgardenplants.com/how-do-you-treat-fungus-on-a-japanese-maple/

https://hort.extension.wisc.edu/articles/purple-bordered-leaf-spot/

If you think there is something else going on with your tree, get back with us or give your County Extension Office a call. They might ask you to bring in a branch of your tree to help with the diagnosis.

Best wishes,