Oh, mighty hive mind of the wonderful intywebs, I need your advice.

How should I deal with mildew on the back of an acrylic on canvas painting?

@lordmatt
Have you tried yelling obscenities at it?
@lordmatt
Although in all seriousness try damping a cloth or such with mildew killificating product and dap dap dapping it and occasionally wiping. Also have some dry dry cloths on hand, along with a lot of time, patience, and effort to spare.