The fungi that causes blue mold, which in its initial stage doesn't effect the strength of the wood, can be controlled in a number of ways. Temperature as the other fellow suggested to is one control. Growth stops below 40*F and above 105*F. Oxygen deficiency stops it and moisture content below 20 % or above the saturation point also stop it. Sapwood is what the fungi thrives on because of the carbohydrates stored in the cells, so its not so easy to stop. You can chemically inhibiting the fungi. Borate salts (Borax) kills the fungi. There are commercial solutions that can be sprayed on such as YardGuard, Timbor etc. These can be obtained from log home supply places like Canadian Log Home Supply (1-800-746-7773)or contact a local sawmill and ask what they use to dip their lumber in to prevent staining. Hope this helps.