Dealing with Mildew on Northern Ontario Log Home Walls

I have a 40 year-old Pan Abode log home in northern Ontario. I have always had some trouble with a bit of mold on the interior walls if anything was pushed up against the outside walls in the wintertime because of condensation on the walls. I have another problem since we installed a woodstove in the basement. I now have a whitish-greenish mildew forming on all of the outside walls near the floor and extending up to about shoulder’s height. I have scrubbed it off but I am concerned about why t