Ring Worm

Anybody have a good remedy for ring worm? I know that a lot of calves get it this time of year but its annoying when it comes in at all the wrong places especially where you really want hair (i.e., tailhead, quarter, etc.). Thankfully we have black calves so we can just paint it come show time so it isn't quite as ugly. But, I was just curious if you guys have had any luck with anything out there. Thanks in advance.