Horsetail

A problem perennial weed which grows in a wide variety of places from boggy ground to sand dunes. It is often called "Mare's Tail", but the latter is Hippuris vulgaris a flowering plant and no relation. There are about thirty species in the world and Equisetum is the only genus remaining in the Family Sphenophyta which has existed for around thirty million years - some of the earlier species reached up to 30 metres in height. All had the unique straight stems with whorls of branches at regular intervals.
There are two types of growth, in spring brown asparagus-like shoots appear with cones at the tips and these produce spores. Later the more familiar thin green, branched stems appear and these remain until the winter. Both are produced from creeping underground rhizomes which can go down about 1.5 metres. In cross-section the rhizomes have six hollow channels and a fleshy core.
Some of the alternative names come from the use of the plant as a pan scrubber, but I'm not sure if it is much use for shaving - this may refer to its use in polishing wood.
The cells contain silica granules which might account for the toughness of the stems - horsetail has been recommended for treating brittle nails and preventing osteoporosis. It also has a diuretic effect and has been used to stem bleeding. The flavonoids contained in the stems have antioxidant properties.
In Biodynamic horticulture a preparation is made from Horsetail to use as a fungicidal spray. Go to the Garden Recipes page for a method of preparing it.

Eradicating this weed is not easy and will take much persistence, continual removal will work - eventually, but must be carried out on the whole area, so may require co-operation from neighbours (it could be worth it to offer to do the work if it will get rid of this pest). Regular close mowing will exhaust the rhizomes, but the patch must be isolated as growth will re-emerge from an adjoining area - the deep roots make using a barrier impractical. Paved areas can have a dense network of the rhizomes underneath, so these will re-infest surrounding ground.
Check early in the year for the cone-bearing shoots to stop the production of spores and remove any of the branched shoots later. Sowing turnips in the area has been shown to inhibit the growth of shoots, probably due to an allelopathic substance produced by the turnip; this would need to be done for a few seasons to exhaust the rhizomes. Small pieces of the rhizome will regrow, as seen in the lower, right picture where a 3cm segment has produced a stem. So cultivation of the area will compound the problem - it may be possible to follow most of the rhizomes by careful use of a fork to tease them up, but they are very brittle and snap easily. Shoots are also produced from small nodules about 0.5cm in diameter, which are solid white flesh inside covered in a dark skin as in the lower, left picture. These have probably arisen on the rhizomes and broken away when disturbed.

It is resistant to most weedkillers, but Glyphosate may have some success after repeated treatment. Crush the stems first by trampling them to increase the penetration as they have a waxy surface due to the high silica content. Some success has been achieved using a selective weedkiller - eg. a spray with Verdone Extra (now Weedol Lawn Weedkiller) causes the topgrowth to die within a few days, but that is not the end of it and the application will have to be repeated a few times. Allow new growth to develop well to increase the surface area which will absorb more of the herbicide. This is a good way to weaken and eventually kill the rhizomes as would constant cutting or pulling the stems. It would be useful for knocking back any inaccessible growth among shrubs or at the base of a hedge - lower the stems carefully to the ground away from the surrounding plants, trample and spray.
A gravel bed which had a forest of Horsetail was trampled and sprayed with Verdone Extra two years ago. It died away and as yet has not regrown so this is some proof that the technique can work.

Follow these links for further details on Weeds, Weed Removal and Weed Prevention.