Horsetail Equisetum arvense Also know as marestail or pipeweed. An ancient and unusual looking plant, horsetail is predominantly a weed of poor soils, spreading itself via an underground root system.

How to kill horsetail weeds:

Chemical Options:
None. Horsetail seems impervious to even the strongest dose of weed killer.

Organic Options:
Improve the soil with plenty of well-rotted manure, the horsetail won't like it and it will disappear.
For a really bad path, nothing beats heap of fresh dung: in the process of rotting into the soil it will eradicate the horse tail, although you may have to issue everyone in the neighborhood with clothes pegs for their noses in the meantime.

Alternative Options:
The Romans used it to clean saucepans with: it contains silica, which gave their saucepans a non-stick coating. But it has recently been found to be poisonous when eaten, so that option wouldn't be recommend now.
Another option would be to pull up a stem of it in winter, and wrap tinsel round it for a cut-price miniature Christmas tree.