Infestation of Locust borers on Black locust tree. Too late for it?

Question

Over this season I've narrowed down my black locust tree to having possible locust borer problems. I used an insecticide tree and shrub drench in June after seeing the tale tell signs, with a ring of wood dust on the ground.

There are little holes sporadically through the tree trunk and branches, and a few small limbs broke from the damage caused. They gave way after some stronger winds, which would have normally held up okay.

This weekend I noticed them crawling all over the the tree (Which seems common for this species in late August and September). Is it better to cut this tree down in November, or spray it with Sevin and try to save it? Will Sevin 500 work? I read Carbaryl is effective and there is a Sevin with Carbaryl in it, but only available for purchase over Amazon or online. No local hardware stores carry it, just the Sevin 500 series. Carbaryl seems to have some possible harmful side effects to humans (more than most chemicals used in insecticides) so I am thinking that's why Sevin with Carbaryl isn't readily available in my local hardware stores, like the Sevin 500.

I've had a previous question for more details earlier in the season: Tree not getting leaves in one section

Answer 1

Well it is hard to say. Borers are a consistent issue with locust trees; the borers do not often succeed in killing a tree outright, but they burrow very deep and can therefore often survive a chemical treatment and will sap a tree of its energy. The result is a tree that looks okay if you look up into the crown, with its nice leaves and white flowers, however the bottom half looks like it has been in a war, with holes and suckers and twisted branches where the tree has tried to repair itself. For these reasons it is more a farm and hedgerow or deep in a forest species than it is a specimen in a yard. I have a patch of about a hundred all grown from one tree planted 20 years ago. They make excellent fence posts since buried locust wood almost never rots.

As soon as a juvenile tree is cut or top growth attacked it will send out subterranean suckers. It's a useful defence mechanism, but this means that in some locations it is an invasive species. If you try to cut your tree it too will sucker over the lawn if it has not done so already.

In short, whether you drench or not, eventually the tree will die off, but quite slowly. You may have 10 years of attractive growth before it finally looks too emaciated to glorify your yard. So plan on replacement when you can afford to cut, wait for suckers, treat, replace. In the meantime it does not look too bad, so no hurry for now.