3% H2O2 (hydrogen peroxide) from the drug store. 1 part H2O2 and 10 parts water in a spray bottle, mist thoroughly. It killed my icky stuff in my jugs last year but didn't have any seedlings yet.

I'll work on what causes that stuff, usually too warm, maybe too moist and whether the jugs should be open and in more sun. I've taped over vent holes in the top of most of my jugs for now but will remove the tape as it starts to warm up. Some I don't bother to punch vent holes.

I've got 12 good-sized holes burned in the bottom of my gal jugs, didn't stop the white fuzzies when I spring sowed (shouldn't have taped the jugs when so warm). The H2O2 got rid of all of it but isn't getting rid of some moss in an indoor plant. I lost most of my seedlings anyway due to that; they hadn't germinated yet. Got two IIRC.

So yes, drainage holes could be an issue especially if they're sitting on wet ground. I set most of mine on the sidewalk since I don't have anything to set them on to elevate them this year.

And no matter what, if the spores were in the soil or jug, you can get that. I do rinse out my jugs but will rely on my H2O2 solution, too much work sterilizing jugs and soil.

Cool, I will try the peroxide.

This is the first year I haven't placed my containers on a picnic table; they are on the ground, so I suspect that's the problem.

I don't know which Z8 you are in, but my own has been warmer than normal (warmest January on record) and wet. Conditions that call for enlarging those ventilation holes or removing lids completely. Of course if a hard freeze does pop up end of February, that could mean covering containers again, but they are 'fuzzing up' because they don't have enough air circulation for the weather they are being exposed to.