Dreadful things! What's the herb? Essential oils kill mites; I've been relying largely on a thymol-based mix for years, though I also use oxalic acid. The thing that makes me hesistant about herbs is that strength is a bit unpredictable, and it's vital as the metabolisms of mite and bee are quite similar, and the dose has to be right to kill the mite without killing the bee. Many treatments (which I refuse to use) are seriously harmful to bees, and persistent in beeswax. Thymol is non-persistent, but temperature-dependent; if it's too cool it doesn't evaporate, if it's too hot it drives the bees out of the hive. Oxalic does harm bees, but one treatment per generation is tolerable. It's a bad one, and the best long-term solution seems to be breeding for resistant bees. A lot of progress is being made on this now, but we're not there yet. Then there are other bee pests on the horizon.
I'd be interested in hearing more.