Some branches on my Japanese maple seem to be dying. It started early last spring (2019) when I trimmed a few branches. I can't seem to figure out what this disease is and how I can stop it. Please let me know! :)
If it is a pothogen, it appears to be moving downward which then means it is in the phloem. Nectria canker is one such pathogen that I've experienced and seen in garden center nurseries in my area. Were this the problem, you should have seen small orange dots, the fruiting bodies, late last summer (around August). Regardless, you should be in the habit of sanitizing your pruners. Isopropyl alcohol 70% to 90% on a paper towel - thoroughly wipe the cutting surfaces before use and, with this tree, after every cut. IMHO, you'd best remove the dead stuff, cutting well below its extent (i.e., at a point in the healthy appearing stem).
Hi Nathan, agree with everything Osoyoung has said. Can I add that looking at what you have said ie cutting the tree back in Spring is not ideal as the sap is rising, this can cause problems for the tree. You should be pruning or trimming when the tree is dormant in Autumn or just before Spring around February. You can tidy 'a little' in July but not too much. If you do as Osoyoung advises re cutting out dead wood now, don't touch it again this year and then start the new regime in early 2021. Good luck.
I see in the photos a land that is too compact and humid and weak roots. If it were mine I would cut all the dry branches, on the healthy side, as you have been told, I would put healing paste, wash the roots and put a substrate with a grain size of 4 to 6 mm. or more But of course it is a very personal decision.
