>It is my experience (which isn't much) that if the bees aren't eating the sugar water, mold will grow inside the jar, or whatever container you have.
> I suppose this is not good, so I usually change and clean out any feeders at least once a week.
I wait until they are empty and then clean them with some distilled vinegar and water.
> Wouldn't mold encourage AFB?
No. AFB is a bacteria that is unrealted to the mold. It MIGHT actually DISCOURAGE EFB, but I wouldn't count on it. I know that the mold that causes Chalkbrood (also a different mold than the stuff in the syrup) kills EFB.