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I'm interested in your experience with cultivars of everything commonly described as a Japanese maple, regarding their disease resistence.

I could not find anything on this topic beyond throwaway comments

Especially curious what people say who had multiple cultivars, over several years, and who dont apply chemicals unprompted. Or who do so and certain cultivars got affected anyway

My Bi-Hoo is contracting Pseudomonas all over the plant, besides the athracnose. A youtuber had warned about this cultivar and bacteria, too. Now I have my confirmation. While healthy it is one of the most beautiful cultivars but I cannot recommend it and will dispose of mine.
My Sango Kaku is similar though the Pseudomonas doesnt start in the middle of branches and for no apparent reason like on Bi-Hoo. I guess one or two twigs got infected on their ends. Might have killed the airlayer last year though.

I do not intend to run an intensive care unit. On the contrary, I want to put maples in a field and have them look after themselves until I dig them up again.
Im sure Im not alone in that.
I have only had fungal issues with the Beni hime cultivar. I have actually lost two of them. The only issues I typically have are if it freezes after leafing out. Some cuttings can be tender and I lose a handful a year. I use Bonide spray once a month during the fall after leaf drop and continue until about May. After that I will spray 1 or 2 times in the summer. For smaller trees you can dunk in a tote and let it soak in. Serious maple propagators use a product called Phyton 35. It is pretty expensive. I am in the southern US and despite the humidity here we don't get the fungal issues some do in colder, wetter climates. With maples black is normally bad news. If they are branches cut them off. With a trunk it is normally bad news and you generally lose the tree. Sango Kaku and Bihou are definitely the ones known to get fungal diseases. Some of the hime types tend to get them too since the canopy is dense. Many sources will tell you not to water overhead but I am not certain I agree. I do think wet roots are the driver which is why I use a fast draining soil.
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