Anthracnose on Trident and Japanese Maples

Continuing the discussion from Trident maple black spots:

Hey @bandi and @Ali10, I am new to Mirai and am glad I managed to find this post even though its been a while. I currently have a Trident and Japanese Maple struggling with the same issue as both your trees were a year ago. I was wondering if they are still healthy and what route was taken to correct the issue? I am pretty sure after a bunch of research that it is a fungal disease called “Anthracnose” which cannot be destroyed or cured, only managed.

@bandi, I see your technique gave you major success. Did you repot right before bud break/beginning of Spring? Did you bare -root all of the old infected soil? Did you spray Fungicide before or after the repot? What type of Fungicide did you guys use?

Spring started about a month ago out here where I am at in Santa Barbara, Ca. and both trees have pushed out a good flush for about a month before this issue started. I think it is too late for me to repot? Both trees are on week two of undergoing this stress and I just received a Fung-onil Bonide fungicide through Amazon that has “Chlorothalonil” as the basic ingredient to treat/manage Anthracnose on Maples. I also have Bonide Copper fungicide that has “copper soap” as the main ingredient to treat Anthracnose but it doesn’t list Maples as a species it treats and I read in a thread somewhere that “Copper Soap” is not good for Maple trees?

@Ali10, Did you end up pruning away infected foliage or did you start fungicide treatment with the diseased leaves in place? What was the outcome?

I’ve kept both trees in indirect sunlight, mostly shade because the leaves seem to burn easy. Drainage seems okay, however the Trident Maple is basically in a partially defoliated state from dropping leaves after they wilt up and die. The leaves that do remain on the tree are infected and some of the new growth already seems infected. The Japanese Maple is still young and in a growing pot and its leaves just started with black spots about a week ago.

I am just unsure how to go about the process, should I prune all the infected leaves and completely defoliate the tree, then spray the fungicide treatment? Or just start the treatment with the foliage it has now?

What do I do if the new foliage continues with the fungal diseases even after a few weeks of following the recommended bottle treatment.

Does this disease spread to other trees?

Hey @Johnny_Chavez

Sorry for replying late. I totally forgot to write back.

So, first thing first, the tree is still sick unfortunately. Just like last year the first flush came out with fungus. Un the upside, the severity is way lower, as much less leaves are affected and the areas on the leaves that have the black markings are smaller, and mostly on the edge.
That being said, I have done some additional research, and have received some info from other bonsaists. It look likes this is a fungus you live with :frowning: It’s very hard to kill it, as it lives in the dead tissue of the tree in the trunk.
This year I will continue treating with fungicides as well defoliate to see if the 2nd flush is still sick.

Regarding the procedure last year.
I replanted in late spring, after leaf out. I DO NOT recommend this. I just took a gamble - I thought, I might as well try a last ditch effort, and apparently it worked, partially.
I did a bare root repot, washed off all the soil, and sprayed with fungicide (copper based). I would need to check the type of fungicides I used, but you wouldn’t find them as they are local products, not international ones.
Also I defoliated the tree entirely during the repot, to make sure those black spots don’t spread any spores on the new buds.

Very Important: During winter I did multiple fungicide dormant sprays, including a heavy wash with a lime-sulphur based solution. The fact that this spring the tree leafed out with less fungus attack than last year, I can’t say if it’s due to last years’ repot or this winters’ dormant sprays. Not very scientific, I know. It’s the best I can share info wise.

Hope this helps…sort of. Sorry and Good Luck


Hello. I have the same problem with my new trident maple. I will spray today Compo Duaxo (it is a universal fungal spray here in germany.) Then I will wait until next weekend that the tree have some time to soak some of the fungicide and then I cut off all black spottet leaves. I will keep you updated.