Pseudomonas syringae?

[penumbra]

So this is why I recommend people proceed cautiously with organics with Japanese maples.

As bonsai yes, but all JMs are grown in the ground or in organic mixes.
Incidentally, all the dead maples were not pruned for a year and roots not touched for two years. They looked fine last summer but did have some powdery mildew at the end of the year. That was of course a warning sign.

 

[Mad Tabby]

I used to use Lysol and bleach regularly. Bleach can be used in spray if you go by smell, it has to be just under where you can smell it if sprayed on a sheet of paper, not at 10% recommended on some articles or in the lab. The real Lysol concentrated kind contains the qac's/ quaternary compound you are likely to get with the brand name bactericide but different emulsifier. Again, at serious dilution can be sprayed but just in case cover soil.

If you cannot find the real Lysol, Detto is what Lysol used to be. You may find it in first aid or cleaning depending on the store. Or farm supply stores carry it.

 

[ABCarve]

I was surprised when I went to their site and saw it was a form of copper. Seems like a huge price to pay. The 18 maples that are dead are in almost 100% 0rganic growers mix that I have been using virtually unchanged for over 40 years. It is a variation of what almost all nurseries use that is tweaked for individual climate and such. It really is not feasible for me two grow hundreds of pots from 4 inches to 20 gallon using a bonsai mix. At any rate, the death seems to have been isolated. I have one significant JM that is on the opposite side of the house in a bonsai mix that may or may not have pseudomonas, but it took a turn 2 days ago and all of its inner leaves turned bright autumn red in the morning and brown a crispy in the evening. I don't think it is the same, hope not. I was repotted fairly late in the season, a few weeks ago, so it may be reacting to that assault.
Thanks for pitching in .

Have you looked into mefenoxam or brand name Subdue. I know bonsai pro who had an issue with this in his nursery and that’s how it was treated. It’s very pricey.

 

[nuttiest]

If you cannot find the real Lysol, Detto is what Lysol used to be. You may find it in first aid or cleaning depending on the store. Or farm supply stores carry it.

No. that is a completely different chemical, a phenolic compound.
Would be like comparing frac group 3 and 7 fungicides