Hello, This morning I noticed on two of my small maples (Sango Kaku and Aka Kawa Hime) lots of small black spots have appeared on the leaves. I'm including a picture of each. This many must have appeared almost overnight because yesterday I didn't notice them. They're not on every leaf and seem to be mostly on the top most leaves of both trees, but there are some on the lower leaves as well. They can't be rubbed off and look like the leaf itself is damaged. The other damage to the leaves (dark tips, crispy edges) is how I received them about two weeks ago (one from a garden center and one an online purchase) and is not new. In doing some research it looks similar to damage caused by aphids, or potentially a fungus? I haven't seen any aphids, but I have noticed a couple little gnats or flies now and then, and have sprayed the leaves with neem oil a couple times since I received them. I did test the neem oil on a few leaves of each tree and it didn't seem to cause a problem, so I'm inclined to think it's not the neem oil itself doing this. The trees are in containers and are near each other, so if it was a fungus that was already on one of them it could explain why two trees now have it. I have a few other small trees that may be starting to show a similar pattern of black spots, but not nearly this bad. I've included some pictures of those leaves as well. Again, the other damage (crispy leaves mostly) is how they were received. It's just these spots that are new. We live near a highway and so I have noticed some dirt/dust buildup on the leaves that I've been brushing off with my hand or spraying off with a water bottle. Not sure if that would cause this. Does anyone have any suggestions?
Good evening, this to me looks like the start of powdery-mildew. It does spread when trees are close together and there is not enough air circulation. I could go on, but I have added this link for you to compare your leaves instead. Maple (Acer spp.)-Powdery Mildew
Thank you for the reply and the link. I haven't noticed any of the white powder at all so I hadn't though it might be powdery mildew. Should I continue to spray with neem oil or is there something else I can try? In my other searching I've seen a product called Daconil recommended.
I would continue with the Neem as it is very effective against powdery mildew and other fungal attacks.
Great, thank you again for your help. I should add that even though they are kept fairly close when I bring them in from the morning sun, the shaded area still gets a good breeze so I think the area has good circulation.
Should I remove the affected leaves? Our summer will be starting soon here if that affects the decision. If so, what's the best way to remove them? Cut at the base of the leaf or remove the entire leaf and stem?
Cut off at the base. I would only remove the most affected tbh, although I do know some who would completely de foliate their tree to stop the spread. Do ensure you burn the leaves that you remove and do not allow any to sit on the ground. Keep a look out for any that have dropped already and remove immediately.
