F benjamina being attacked by borers

[TimIAm]

This tree was an air layer but due to dieback was quickly attacked by some sort of borer. There were tiny grubs far underneath the bark, so I exposed all of the dying bark and things looked ok.

At the time I started the layer, I wired this side branch but the tree in its weakened state didn't like that and where the wire was it cut bad into the bark. After removing the layer, I also removed the wire. About 6 months after I removed the layer I noticed that some borer grubs had almost ring-barked the branch at the site where the branch meets the trunk. I cleaned the site up and put putty completely around the branch to try and keep it alive.

The branch has put out some new growth this spring (southern hemisphere) but this morning I decided to have a peek underneath the putty and noticed there were two tiny grubs there and the site looks worse than when I put the putty on.

You can see the top has put out much more growth than the side branch, but the side branch actually existed before the top when the layer was started.

I really don't want to lose the side branch as I think it will take years to replace if it goes. I also think I've got something unique to work with, so I'd like to save the branch and the tree.

2 questions:

- How can I make the existing deadwood less appealing to borers, grubs and anything else that attacks it?
- Any suggestions for keeping the branch alive?

With putty on the branch it was kept moist. Not sure if I should keep it exposed?

 

[Shibui]

I would treat deadwood with lime sulphur. That seems to deter almost anything so I guess it should also stop borers but may depend how far it penetrates. Ficus wood is generally very soft so it will almost certainly rot away even with regular treatment.
Borers normally target either dead or live wood, not both. If they are eating the dead wood I don't see how they are also affecting the live sections.
If they are eating the live section there's probably no point worrying about the dead wood as far as borers. A systemic insecticide should stop anything from eating live wood, leaves or bark.

 

[TimIAm]

I would treat deadwood with lime sulphur. That seems to deter almost anything so I guess it should also stop borers but may depend how far it penetrates. Ficus wood is generally very soft so it will almost certainly rot away even with regular treatment.
Borers normally target either dead or live wood, not both. If they are eating the dead wood I don't see how they are also affecting the live sections.
If they are eating the live section there's probably no point worrying about the dead wood as far as borers. A systemic insecticide should stop anything from eating live wood, leaves or bark.

I haven't had a good experience with F benjamina so far. The problem being that every time that a cut is made I get die-back from the existing bark. Also, when I was doing some removal of some parts of the exposed wood, there was still some latex/sap inside parts of the wood. I want to carve the dead wood section eventually, for now I just want to keep this tree as healthy as possible, so I've avoided further cutting into the dead wood. I hear what you are saying about the dead section not being directly related to the living part, but I'm worried that the borers will cause further damage to behind the bark and cause more die-back.

I don't enjoy working with lime sulphur, but maybe I will give it a go and see how the tree holds up between now and autumn.

Fully understand that rot is going to happen with this tree, but I'm still hoping I can have a living tree in another 10+ years.

 

[Shibui]

I haven't had a good experience with F benjamina so far.

Your experience is not unusual. They can be quite temperamental. Do yourself a favour and get some Ficus rubiginosa - PJ fig. It grows all round Sydney so is ideally suited to you and is much, much stronger and resilient and grows much faster than benji.

 

[MHBonsai]

Benjaminas will die back to the next healthy growing tip. That’s the challenge with them.

I’ve used this stuff to good effect.

https://www.minwax.com/en/products/maintenance-repair-tools/high-performance-wood-hardener

And also coating deadwood in two part clear epoxy under the soil line. It’s fighting a losing battle though if it keeps getting wet.

I’d try to nuke all the bugs and carve out any suspect areas then drench/dip the dead trunk in wood hardener.