What should I do if stem borer attacked some of my plants? Any suggestions for actions?

Bayer Advanced Tree & Shrub is the only product I've ever seen with Imidachloprid in it other than a very potent flea killer for dogs. It's good against a lot of insects but be careful where you use it and read the warning label.

Stem borer entrance should be visible you can use metal coat hanger and spear the little rascal if you don't like using pesticides.

Any experience with neonicotinoid insecticides for stem borer? Maybe inject some Mospilan to the entrance...

What do you think?

Thank you very much.

I have acetamiprid at home....

Neos kill honey bees and other pollination bugs

Great topic.
I chose to sacrifice the infected trunk since those beetles usually stay away from healthy wood and are attracted to dry or dying wood anyway.
The trees put out new shoots in no time and I have not seen those things in two years now.
Best of luck with your trees and if you chose to cut them down make sure your burn the infected limbs.