How to Control Carpenter Bees
When it comes to carpenter bees, your best defense is a good offense. Carpenter bees prefer to excavate untreated, unfinished wood. You can discourage, if not prevent, carpenter bees from nesting in a wood structure by painting or varnishing the lumber.
If carpenter bees are already a problem, you will need to use an insecticidal dust to treat the nests. Insecticidal dusts are usually applied with a puffer that allows you to coat the interior surface of the entrance holes with the insecticide using a gentle burst of air. Contact your local extension office to find out which insecticides are effective and legal for use on carpenter bees in your area.
For the insecticide to work, the bees much come in contact with it as they crawl through the entrance hole of the nest. Apply the appropriate insecticidal dust in the spring, just before adults emerge to mate. Once you see the bees emerge, wait a few days before filling in the nest holes with wood putty or filler.
If you didn't apply the insecticide before the spring adults emerged, you will need to treat the nests twice – once in the spring, and again in late summer, when the next generation of adults is foraging. Because bees will be active during the day, it's preferable to apply the pesticide at night. This will reduce your chances of being stung by females trying to defend their nests. In the fall, seal the nest holes with putty or filler.