You'll need to get to the source of the problem. Mold thrives on moisture. It isn't really possible to give suggestions without knowing the cause of the trouble.
A couple of recs. Run A/C more. Run a dehumidifier (costs about 30-60 a month in elec.), add an exhaust fan for the basement (this does work, and is cheaper than dehum.)
Can't say much more, no chemicals will resolve this issue.