A trench treatment will not kill Drywood Termites because Drywood Termites nest in the wood unlike subterranean termites that nest in the ground. The best product to treat and prevent Drywood Termites would be
BoraCare. You would simply mix 1 gallon of
BoraCare with 1 gallon of water to make 2 gallons of finished solution (enough to treat 800 sq ft of attic or crawlspace) and spray the wood in the attic space and/or crawlspace.
Boracare contains an inorganic borate salt, soluble in water, with insecticidal and fungicidal properties effective against wood destroying organisms. A patented carrier system allows
BoraCare’s active ingredient to diffuse into wood. This system makes
BoraCare more effective than products designed to treat only the wood’s surface.
BoraCare also stays in the wood for the life of the wood, it never goes away so it will prevent future infestations in the wood that has been treated.