Equisetum arvense (the typical plant)
Field Horsetail, Common Horsetail, Lego Plant, Bottle Brush, Cat's Tail, Colt's Tail, Frog Pipes, Horse Pipes, Mare's Tail, Scrub Grass, Shave Grass, Snake Grass and Snake Pipes.
These plants fuelled the Industrial Revolution. They also were an invaluable part in the production of the magnificent English Japanned cabinet furniture of the early eighteenth century. They made the finish on the unequalled architectural limewood carvings of Grinling Gibbons, during the same era. They have been around, largely unchanged, except for size, for over 300 million years. They have developed uses in folk medicine in many parts of the world, yet are highly poisonous to livestock. Now, as climatic and environmental shifts are stirring, so they are beginning to awaken again and become increasingly frequent and damaging even in their native ranges. In the UK , the term "noxious weed" is certainly justified, but the characteristic environmental degradation and ecological change brought about by true invasives, does not occur.
In botanical terms, Horsetails are cousins of Ferns and Clubmosses, (Pteridophytes) and are fairly primitive, non-flowering plants known as Arthrophytes. Giant, tree-sized ancestors of today's horsetails formed an important component of the upper carboniferous period forests. These ancestral plants became fossilized as coal, and so became the energy source for industrialization. Now only about 25 species exist worldwide, mostly in the northern hemisphere, but they are by no means on the way out.
A characteristic of the genus is the habit of depositing crystals of silica in the leaves and stems, which make them abrasive to a greater or lesser extent. Before the invention of glasspaper, a native, branchless horsetail, more common in continental Europe, Equisetum hyemale, was imported dried from Holland , and known as "Dutch Rush". This was used for finishing wood, and for smoothing the surface between applications of coats of lacquer. On the Grinling Gibbons limewood carvings, its use left minute and characteristic striations on the carved wood surface. In the USA , E. hyemale and close relatives were known, by the early settlers, as "scouring rushes".
The plants contain a large number of chemicals both organic and inorganic, of which at least 80 have been analysed and identified. This chemical richness and the synergistic potential there from makes horsetail of use in herbal medicine in many areas, especially in connection with the blood, the urinary system and tissue-healing. Astringent, anti-haemorrhagic, anti-inflammatory and diuretic properties are scientifically documented. The toxicity to livestock, especially horses, seems to be related to the presence of the enzyme thiaminase, which combines synergistically with an undetermined selection of other chemicals in the plant to produce severe and distressing neurological symptoms, sometimes leading to death. As with Ragwort, the most likely source of poisoning is via horsetail included in hay.
In the UK , The Field Horsetail, Equisetum arvense, is a noxious weed in market gardens, orchards, nursery stock producing establishments and in landscaped areas. Fortunately, American experience of horsetail as a weed of arable crops is not repeated here. Increasingly, however, it is appearing in the newly built environment, popping up through tarmac, between paving slabs, at the upstands of walling etc. If this sounds like Japanese Knotweed behaviour, then there is another similarity.
Horsetail gains its vigour and resistance to control by means of an extensive system of rhizomes, possessing substantial food reserves. This system may penetrate vertically to a depth of 2 metres, with multiple horizontal branches to a maximum of 1.5 metres depth.* Most of the horizontal rhizome system is usually contained within the top 25 cm of soil. Nodes are produced at 10-12 cm spacings along the rhizomes, and these can give rise to both aerial shoots and true roots. Where the rhizomes branch, rounded tubers 15-20mm in diameter are produced, mainly at depths of greater than 50cm. These serve both a food storage and reproductive function. Carbohydrates are stored from May until November, well after the time of maximum vegetative growth, and detached tubers readily give rise to new plants. The number of tubers produced can be very large, with up to 1000 being counted in a metre3 of soil.
The rate of rhizome growth is quite startling. A 10cm length of rhizome has been shown to be able to produce 64 metres of new rhizome within one year. Rates of growth such as this enable horsetails to infest 1 hectare of land within 6 years of introduction.
Field Horsetail is a rhizomatous perennial, hardy to temperatures as low as -45°C. It grows equally well in all types of soil, given reasonable moisture. It is, however, frequently encouraged by poor drainage, acid conditions and soil compaction. It reproduces by extension or fragmentation of the rhizome system, by detached tubers and by spores. In common with many problem weeds, Horsetail can regenerate from a single rhizome- node. It is resistant to eradication by all mechanical means, and chemical controls seem to vary widely in effectiveness even when active ingredients, timing and application methods remain the same. The resistance to chemicals is partly due to the siliceous deposits in the stem cuticles, which form a barrier to herbicide absorption, and thus reduce the amount that can be translocated through the system of rhizomes.
Another interesting characteristic of these remarkable plant is in their ability to absorb heavy metals from soil. Accumulations of Cadmium, Copper, Lead and Zinc have been found, but its real preference is for Gold! Levels of 130gms/tonne of fresh plant material have been recorded.
* I have read anecdotal evidence that horsetail rhizome has been found to a depth of more than 50 metres in brick earth workings.
Taxonomy and Biology
A dimorphic, rhizomatous perennial, producing fertile, spore-bearing stems, devoid of chlorophyll, during March and April, followed by green vegetative stems from late spring to frost. Rhizomes dark brown or black, pubescent, bearing rounded tubers. Vegetative stems to 90cm, green, 6-14 furrowed, rough with nodal verticils of solid 3-4 angled branches. Leaves very small, scale-like in a sheath around the stem node. Fertile stems to 25cm, before vegetative stems and soon withering, pale brown, succulent, without branches. Leaves in a larger looser sheath than on vegetative stems. Strobilus lanceolate to ovoid, pedunculate, not apiculate.
Horsetails are the only living representatives of a division of plants called Arthrophytes, so called because of their jointed stems. The modern folk name "Lego plant" derives from the fact that the fertile stems can be pulled apart at the joints and put together again like stove-pipes. Amongst the extinct relatives whose remains are found in the coal-measures, were trees of the genera Equisetites and Calamites. Equisetum hyemale* first appears in the form of pale, brownish, fertile stems which are present during March and April. Each has at its tip a conical spore-producing organ, the Strobilus, which can be about 3cm long. When ripe, this organ sheds in the region of 100,000 spores, which germinate readily on any damp substrate, but are otherwise short-lived. Initially, male or female pro-plants, known as Gametophytes result from this germination. Cross fertilization of these pro plants produces the development of a true sporeling, which soon develops a shoot apex and roots. When established, the sporelings become rhizomatous and grow as mature horsetails. The parent fertile shoots wither after spore production, but are immediately followed by the familiar fir-tree like vegetative horsetail stems. These stems are the photosynthetic stage of the horsetail, and foods manufactured in the stems and branches are stored mainly from May to August, as maximum vegetative growth is reached and passed. At the time of peak growth, about July, the storage tubers (already described) start to develop on the rhizomes, and may continue to increase in size until November. More acid and sandy soils seem to encourage tuber production.
The stems persist until frosts, then die away and decay during winter quiescence, during which time the plant survives as a system of rhizomes and tubers.
Glossary of terms
Apiculate: Bearing a short, sharp, non rigid point
Dimorphic: Occuring in two dissimilar forms
Lanceolate: Lance shaped, tapering to a spear point
Oviate: Egg shaped
Pendunculate: Having a stalk (as of a flower)
Perennial: A plant lasting 3 or more seasonal cycles
Photosynthesis: The synthesis, in green plants, of complex organic molecules, by the action of solar energy on carbon dioxide and water
Pubescent: Covered with short fine hairs
Rhizome: A specialized underground or surface stem
Spore: A basic reproductive cell, capable of developing into a specialized plantlet
Strobilus: A cone shaped, spore bearing organ
Tuber: A swollen root (in this case) used for food storage
Vegetative: Pertaining to growth, non reproductive
Verticil: A whorl or ring of structures radiating from a node
* Other UK and Eire representatives of the genus are; E. hyemale, E. x trachyodon, E. x moorei, E. variegatum, E. ramosissimum, E. limosum, E. x littorale, E. palustre, E. pratense, E. sylvaticum, and E. telmateia. None of these others is a major weed, and some are very rare.
Tenacious to life through hundreds of millions of generations; impervious in its armour of silica and older than most hills; this survivor from an era when primitive amphibians were state-of-the-art and Tyrannosaurus 200 million years down the line, is very difficult to kill. Mechanical methods vary in efficacy from making matters worse to limited success following persistent and repeated work. There are no known biological agents useful in its control and it responds to herbicides in a very inconsistent manner. There is no evidence that any herbicide or herbicide mixture can eliminate it at one spraying; nor have I encountered any verified statement to the effect that even with repeat applications, anything more than good suppression is possible. In landscape and some arable situations Horsetail may be discouraged by improving soil texture, relieving soil compaction and installing effective drainage.
Raising the pH of the soil by applications of lime can also reduce the vigour of the weed. Horsetail has a very limited response to increases in soil nitrogen availability, so ensuring vigorous growth of field crops, by maintaining high fertility, can lead to suppression of horsetail through light competition. Because the vegetative stems have no functional leaves, the plant's light requirements are high, and it is also possible to suppress the weed by applying a dense non-woven mulch sheet, such as black polythene. Woven geotextile mulches should not be used as it is documented that stems have some ability to penetrate the spaces within the weave.
It is theoretically possible to cut or pull every stem and all subsequent regrowth as many times as needed for 3 or 4 seasons. By this means substantial reduction in stem densities can be achieved. Any attempt at control by similar means, for one year only, will fail. Canadian researchers performed 16 hand weedings of a test plot in one season. The following year the weed density was identical to the unweeded control area! Where the weed is present in lawns, close mowing will eradicate it over a period of years. Other mechanical cultivation of infested areas should never be attempted, as this will simply detach tubers and initiate their growth, as well as spreading and fragmenting rhizomes.
A number of chemicals are known to have some effect on Horsetail. Dichlobenil granules applied before growth starts in the spring to non-crop areas can eradicate the problem in 3 seasons. (personal experience) The application rate for total vegetation control on non-crop areas should be employed, as that used for weed control amongst woody subjects is ineffective. Where top growth is to be sprayed, the stems should first be bruised or crushed to damage the cuticle with its protecting silica, thus allowing absorption. Some sources suggest that Glyphosate is effective after this treatment; others indicate it has little value.
MCPA can reduce the stem densities of infestations, by about 30% a season if applied annually, though the arithmetic alone suggests eradication would take many years. In arable crops in the USA , a number of ALS inhibitor type herbicides give control, sometimes in formulations also containing Dicamba. The relevant ALS compounds are not, however approved in the UK . Ammonium Sulphamate is known to be effective against Horsetail. I have read anecdotal evidence that eradication is possible in two seasons by this means. back to top