I need to treat some larch (?) laps on the side of my shed (not ship lap) which have some woodworm. I have used the small Rentokil can where you squirt into the holes but I think the strips really need a brush application to soak them. The only woodworm treatment I can find is for interior wood only, even a local well known shop is advertising on it's site exterior/interior treatment but the can states only for interior. Can anyone suggest a treatment for external wood? Thank you for any advice you may be able to give.