Japanese Maple - roots rotting, fungus or something else? HELP

[Tokar]

Hello Everyone!
I need help. I have a Japanese Maple for 3 years (it is around 8-9 years old). It was doing fine until recently.
Everything started when I put a fine, solid fertilizer on top of the pot, that turned into a moist layer. I discovered larvae in soil, probably caused by this fertilizer. I scratched off the fertilizer and some layer of soil from top, removed larvae and put on top new soil (mixture of organic soil, Akadama, lava and pumice). I waited 2-3 weeks, the tree started to release some buds even, but they all stopped growing or started to dry out. Even few days ago I noticed some new, red buds that don't develop any further.
Today I noticed some discolorations on bark, I scratched it and it's brown and mushy underneath (although in the other place it is still green after scratching a bit of bark). There are no leaves at all, all dried and fell. I might have overwater it, so I suspect roots rotting. I attach some pictures where you can see the tree, the discoloration with a place I scratched and also roots (I just lifted the tree from the pot gently, soil was quite wet). Some branches also seem like they slowly die , turning dark brown/black.
Roots are brown, but not really mushy as they describe in the Internet. I don't know what to do now, is it too late to help it?
I think to repot it, remove partially roots that don't look good and use only inorganic soil for better drainage.
The question is now, if it was indeed overwatered, should I water it after repotting? And how much then, how to recognise when to water? Should I use some root activator, to promote root growth? Or are there any other fertilizer-like supplements to support a sick tree after repotting?
Thank you very much in advance, I really love this tree and would like to save it.

 

[Shibui]

Based on your description, the photos and prior experience, I'm confident that tree is well past saving.
If it still had a healthy trunk I would say try an emergency repot to try to encourage new roots but it is well past that point.
I doubt that the fertiliser caused the problem. Root problems start well below surface level and many weeks before you begin to see symptoms so almost certainly coincidence that you applied fert when it was about to show signs of root rot.

Location is always an important factor for anything to do with plants and bonsai in particular. Adding a location to your profile helps other experienced members to make advice much more specific to your area and needs. It can sometimes also give us valuable clues to help diagnose some problems.

 

[Tokar]

Thank you very much. My location is Germany. But what could cause this? In early spring it was fine, new buds and branches even appeared.
So is it rotting roots? How can I avoid this in the future (for other trees)?
I will try to repot, I can't leave it like this. Is it worth putting some root activator while repotting or it would rather cause more damage?

 

[Shibui]

All the symptoms point to rotting roots. The black bark seems to be a secondary infection that comes after the roots are infected. Healthy roots should have white tips.
I've found that the longer since repotting the more likely and easy root rot becomes. Most times here it has been in trees that are several years since previous repot. I suspect that roots filling the soil spaces means less air and more water retention so watering regime was Ok last year becomes dangerous this year, especially through the wetter, cooler months and early Spring period.

Several things can help avoid root rot in bonsai.
1. Use more open, better drained soil mix. Usually means you need to water more often but also means it is much more difficult for root rot to start. Your soil mix appears to have some good sized stone particles but also lots of much finer organic material.
2. Check soil moisture well below surface level before watering. Relying on the surface layer does not accurately monitor water levels deeper in the pot. One method frequently offered here is to leave a wood stick - chopstick or skewer - in the soil. Pull it out each day to check deeper soil moisture.
3. Ensure that pots are elevated with plenty of air flow. Problems are much more common where pots are sitting on the soil or on a solid bench during cool, wet weather.

 

[Tokar]

Thank you for a very good description. The tree was repotted last year though.
Maybe it's a lost case but I really want to try. What more can I do to try to save this tree?:
1. Root activator?
2. Some fungicide on bark/roots where it's dark? If yes, what kind of?
3. The soilmix I want to use is Akadama,pumice and lava rock

Thank you in advance

 

[rockm]

Thank you for a very good description. The tree was repotted last year though.
Maybe it's a lost case but I really want to try. What more can I do to try to save this tree?:
1. Root activator?
2. Some fungicide on bark/roots where it's dark? If yes, what kind of?
3. The soilmix I want to use is Akadama,pumice and lava rock

Thank you in advance

unfortunately none of that is going to make much difference. The trunk of this tree is beyond saving. It is fatally compromised and not really capable of functioning. The discoloration is dead tissue. If there were a hint of healthier green there might be a slim chance but I don’t see any

Live and learn. FWIW almost all serious problems with bonsai begin with soil roots and watering.

 

[Tokar]

The tissue is green in some other places, I checked by scratching a bit of bark, it's not fully dead. Even a week ago there were new bud appearing but dried and stopped developing. I will do my best anyway.

Thank you for help

 

[delta6]

Your description and the pictures are pointing towards root rot. A lot of bonsai wants to get dry too. In order for you to know if you need to water or not is to just simply put your finger deep into the soil or use the chopstick method. If you feel moisture inside (using your finger) or when you pull out the chopstick and there are soil/dirt sticking, do not water. Let it get dry for a few more days. Just keep checking until you figure it out. In summer, the soil will get dry faster so you may have to water more frequently. In winter, it may be every week or so..it just depends on your weather. The chopstick method will help you a lot figuring this out for the whole year just to give you a baseline of when to water.

* also, don't repot often coz that is very stressful for the tree. This tree might be beyond saving but leave it alone and see if it will recover...just don't keep your hopes up and don't keep watering it.

 

[rockm]

The tissue is green in some other places, I checked by scratching a bit of bark, it's not fully dead. Even a week ago there were new bud appearing but dried and stopped developing. I will do my best anyway.

Thank you for help

The buds that open and don’t develop are yet another sign the plant is unable to continue on. This buds open because they aren’t dead yet but fail to open because the trunk tissue below them can’t supply them with nutrients etc.