A plug of deformable material such as wood or plastic, for tightly sealing a cylindrical recess provided in wood, in which recess a crushable ampulla with a wood attack combating agent can be accommodated, said ampulla being attachable in a cavity of said plug by means of spring lugs, said plug being provided with a conical drive-in surface, and at least one deformable sealing clamping means being provided on said plug; the plug, at the end facing away from the drive-in end, containing a separate clamping sealing means for engaging the inner circumference of the recess, the outer radial dimensions of the sealing means and of the plug being such that complete sealing is acquired and maintained without damaging the wood after the plug has been driven-in into the recess, even in the event of high pressure-build-up in said recess.