Hey all,
I have a Japanese Maple that went without water for a week in 90+ degree temps. (The watering system failed while I was out of town). Zone 8, soil is a mix of 30% pumice, 70% pine bark.
As you can see the leaves have shriveled up and are now falling off (but the branches are green underneath the bark and still flexible). I’m more concerned about this blackening in the main trunk and what I should do about it. It’s spreading up and down about a quarter inch each day. Not sure if it’s a form of sunburn, general dieback, or a fungal issue (like phomopsis) now that the tree is in an incredibly weak state.
Health ID and possible actions would be greatly appreciated! Photos below show the spread and progression over 3 days,
The areas that are turning black are dead, the green branches are still alive. They can still photosynthesize if there are any living roots left to hydrate them. About all you can do now is water the tree and wait to see if it will pull through. Don’t overwater it as it won’t be using much water with no leaves to transpire. I would keep it in a shady area. As long as the bark stays green it is still alive. It may not put out any new leaves this year, but if the bark stays green it may still leaf out next year.
Would you attempt pruning at all if the dieback continues down the main branch? I know it’s a risky operation in the peak of summer.
I wouldn’t do anything at this time, just let the tree do what it’s going to do.
I have seen this in some of my JMs. The black area is dead and will not recover. If that area is dead from a fungal infection from the old cuts (and weakened condition of the tree)the fungus will work its way down the trunk to the roots and kill the tree. I suggest you saw off the top well below the black in a green area and seal with liquid cut paste ( if you have some the one with 3% fungicide) and then cut putty. I am in Zone 8 near Charlotte, NC. Our high humidity has plenty of fungal issues. I have had very little success using systemic fungicides for this issue in JLs both Bonsai and trees in my landscape.
I’m going to assume the tree is without leaves doe to the heat stress? It is definitely in a weaken state so susceptible to fungal attack. I came across a blog referring to using lime- sulfur to treat for many conditions inclusion fungal and bacterial. Once you remove the dead areas and seal them you can do a preventative spray of the entire trunk and the soil with the lime-sulfur, dilute 10ml/liter and spray liberally. This is a quick effective preventative measure to try to stave off other issue. Do this before any new buds push!
Link to blog for reference! Good luck
Thank you all for the replies and feedback. I let the tree do its thing initially but the dieback started to hit the top of the trunk, so I did a cut-back, leaving 2 rings intact on the trunk. Fingers crossed for bud push but I have my doubts.
@Dave28227 I’m also in Zone 8 (central TX) and I feel like the humid and rainy springs followed by hot and humid summers is a tough environment for JMs.
@SCBonsaiGrower I’m realizing how hard this stuff is to find locally. Even though this is labeled “Jin Seal” could this work? https://www.wigertsbonsai.com/product/lime-sulfur-4oz/
Jin Seal and full strength (30%) lime sulfur are for sealing dead wood. Use any cut sealer to keep out a new infection on your maple trunk chop. The sealer does not have to be a bonsai product if you have some pruning tar or even wood glue they will work to keep out infectious spores and keep moisture in the trunk. Your pic of the trunk cross section has a small thin black line in the 5 to 6 o’clock position which looks like it could be some infested tissue under the bark. You can try some systemic fungicide. Watch to see if there is more die back or cut off another piece of the trunk.
