Question

laburnum  

laburnum detail   We have a beautiful mature laburnum, recent photo attached. We moved to the house 2 years ago. We noticed a side plate sized disc of dark blister like area on the bark last year. I've tried to zoom in on this in the 2nd photo. Can take a specific one of the problem area if that helps. The area is much much larger this year, all on the same side of the tree (facing west) but now spreading over a height of 4 feet, in patches. Where the bark has split we've peeled little bits back and if you are quick some very small beetles scury off under the bark. If seems to be an infestation. But of what we do not know. I've not managed to catch one of the bettle yet, but I keep trying. Any advice welcome.
Thanks
Jeremy

Answer
Sounds like a borer has attacked the tree. The borer enters the bark usually through a wound and bores under the bark and/or into the wood. The small insects you are seeing under the loose bark is not the borer but other insects feeding on the fungi that is growing under the bark and these are not what is causing the problem. I would treat the tree with an insecticide. You can spray the trunk with an insecticide called Onyx or Merit. These will soak into the bark killing the borer in the trunk. The active ingredient in these insecticides have several common name brands. Imidacloprid has many brands and formulations for a wide range of uses, from delousing or defleaing animals to protecting trees. Selected brand names include: Admire, Advantage (Advocate) (flea killer for pets), Confidor, Conguard, Gaucho, Hachikusan, Intercept, Kohinor, Mallet, Maxforce Quantum, Merit, Nuprid, Optrol, Premise, Prothor, Provado, Turfthor, Temprid (Bayer), Winner, and Xytect. The label should have something about borer control written on it.

If you have a sprayer (a regular pump up type sprayer) and can reach the trunk. Spray the areas on the trunk  that do not look normal .  Borers attack trees under stress so I would also fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good.  Check with your local garden type store for thee insecticides.