Japanese Maple has holes in trunk & branches with sawdust

Hello folks.

First of all I have to apologize to ask for advice for tree thats actually not in a container but has been planted in the ground last autumn.

I am from Vienna - Austria & have started doing bonsai about 2 years ago and i love the mirai community so i thought you guys can help me here.

So about the maple:
As you can see, the trunk and the branches have significantly large holes mainly in the junctions. Two branches have actually cracked and fallen off.

The tips of the leaves are constantly pointing downwards, although water can’t be the problem.

Do you have any ideas what is causing this? Can this be treaded?

Thx so much in advance

Looks like some sort of borer. Run a stiff wire down the holes to see if you can skewer it. You can also inject insecticide, particularly if the holes run downwards.

Borers tend to eat the xylem & phloem and cut off the transport of water and nutrients. You may have to cut back to below where the borer has travelled to save the branch.

This was a general comment and not based upon specific information related to borers in maples. Please use more specific information when available.

Thanks a lot for your prompt reply.

I just tried skewing potentiel borer insekts, didn’t seem to have much effekt.
I will try insecticide also.

From your general experience, would you cut branches at this time of the year still & close with cut paste, or would rather wait for spring to make bit cuts?

Also, there are big wholes on the trunk were big branches broke off. Do i want to open up the whole hole & put cut paste on? (which goes significantly down the trunk) Or would i rather fill the hole with something. Maybe cutpaste without opening up the trunk ?

Greately appreciate all the input.

Cheers from Vienna


I would apply the insecticide into the holes with sawdust and then plan to do any cut back in the late winter. The problem with cutting back now is that you will probably get a more die back over the winter - early August would probably have been fine. Japanese maples tends to bleed quite a bit of sap when growing strongly so the goal is to do the cut back after the worst of the winter freezes, but before they really start to grow.

I would carve the big wounds from the branch breakage to so that water drains out of them. The current thinking is to not seal wounds in landscape trees, but I would probably apply cut paste to any exposed bark layers from your carving to slow further die back.