Carpenter bees are a persistent pest in certain parts of the country. The most important step in integrated pest management (IPM) for carpenter bees is to seal wood if possible, since they are much less likely to bore into sealed wood.
For control, exempt botanicals are an excellent choice for a few reasons. First, they are fast-acting and highly repellent. This provides quick kill and makes treated areas undesirable for reinfestation. In addition, they are not subject to impervious surface application restrictions, so there is freedom to apply over large areas on structures if needed.
A wettable dust can be dusted directly into holes in dry form, and then diluted and sprayed over surfaces in liquid form for long-lasting kill and repellency. Seal holes with caulk or plugs after treatment. Remember that wettable powder products can leave a light visible film of powder when dry, so be mindful — particularly on darker surfaces — and test first.