carpenter bees below wood deck

To whom it may concern …

My carpenter bee problem exists below my untreated wood deck. The homes they've created are not the floor boards, but rather the joists underneath the floor.

Although the deck is 16' x 20', I feel they are " only " inhabiting 10% of the total area. To access their nests they are squeezing thru the 1/4" to 3/8" gap between boards. As the crawlspace under the deck is minimal, I've only been on the attack from the top of the deck floor using a white, foam spray that does an exceptional job as they try to squeeze back into their homes.

My problem is I  really have no way to get to their 1/2" bored holes w/o ripping out 6 or 7 floor boards. I am concerned as in 4-days of the ongoing battle I've killed 45 to 50 of the varmints, and there still is activity.

If I use the CYPERMETHERIN, I'll only get it between the floorboard cracks and maybe a small portion on the face of the floor joists. Will this minimum contact with the CYPERMETHRIN low down their activity, or possibly even be fatal?

Thanks in advance for your thoughts.

Getting the dust into their holes would be important for long term control as explained in our CARPENTER BEE CONTROL ARTICLE. That being said, it's not going to be a practical option in your situation. But there are two you can try.

First, if the space between the deck planks are fairly tight, the bees are likely to touch them as they crawl in and out from underneath. A good dusting with either the DRIONE or the DRIONE REPLACEMENT DUST KIT will get dust up under the deck planks. It's a light dust and will fly around coating the exposed wood surfaces quite well even without being able to make a direct treatment. As the bees fly down and crawl into these entrances, they'll pick up the dust and this will cause them to die. The drawbacks to this approach is that you won't be able to treat their nests directly and the treatments won't last as long as they could since the dust will be exposed. I would try to treat once a week until if you use the Drione till I didn't see any activity and then I'd quit.

The second option would be to apply Cypermethrin. But instead of the liquid EC formulation, go with the CYPERMETHRIN WP. This will lay on the wood quite well and last much longer than the dust so in the end, would prove to be an effective treatment. Be sure to get the material sprayed into every entrance way they're using. This will insure good coverage.