Dichlobenil in the spring.

You have those over there, too? The dichlobenil just controls it, but doesn't eliminate it, right? Only thing growing in the arsenic tailings at the Tacoma smelter site is field horsetail; this Carbon Age relict is pretty tolerant of toxic substances.

Control is the best one can hope for with horsetail. In my opinion, it's impossible to get rid of.
We use very low rates of dichlobenil every year and rarely have a problem with it that year. The areas that get missed however get infested. Put it on as soon as the horsetail begins to show. It will stunt any small sprouts up to about one to two inches.

How old is the horsetail plant?
300,000,000 years?
Is it carbon dated?