Bottle-brush, horse pipes, mare
Equisetum arvense L.
Field horsetail is widely distributed in the UK in meadows, gardens and on wasteland. It grows strongly on arable and grassland but is a particular problem in fruit and other perennial crops, and in nursery stock. Field horsetail is a common garden weed. It flourishes on damp soil.
Horsetail has the ability to accumulate gold in its tissues as well as cadmium, copper, lead and zinc. The accumulation of silica deposits in the stems gives them a rough, abrasive texture. Extracts of field horsetail make an effective fungicide and have been used to treat blackspot on roses and rust in mint. It has herbal uses too.
The plant is toxic to sheep, cattle and horses being poisonous in both the green state and dried in hay. The related marsh horsetail (E. palustre), a weed of wet, low-lying grassland, is also poisonous to livestock.
A rhizomatous perennial, field horsetail produces fertile non-photosynthetic spore bearing stems in March-April followed by green vegetative stems in late-spring. The cone bearing fertile stems develop from subterranean buds formed the previous summer and persist for about 10 days after emergence. The single cone on each fertile stem can release 100,000 spores that germinate quickly on moist surfaces to produce male and female gametophytes that mature only within a narrow range of conditions. After fertilisation, cell division results in the formation of a shoot apex and roots. These sporelings soon become rhizomatous and quickly develop successive layers of horizontal rhizomes at 30 cm intervals as growth continues downwards. The early stages of development are very susceptible to desiccation and few new plants are produced from spores but once established the plants become resistant to dry conditions.
Maximum vegetative growth of field horsetail occurs in July. Stored food reserves are used up from late-April to mid-May and the reserves are replenished from mid-May to August. The rhizomes grow rapidly in June-July and continue to elongate beyond October. The rhizome system can be extensive both horizontally and vertically and may reach over 1.5 m deep depending on substrate and water table. Over half the rhizomes are found in the upper 25 cm of soil. In fallow soil and where there is little crop competition more rhizomes are found at shallower levels. Tubers are produced at the nodes of the rhizomes and may be present singly or in strings of two to four. Tubers are initiated in July and formation is thought to be influence by soil pH and soil type. Tubers may continue to grow in size and number until November. Rhizomes may produce numerous tubers, 300-1,000 per m³ of soil. Most of the tubers are found below 50 cm depth.
Vegetative reproduction and regeneration is by detached rhizome sections or tubers. Rhizome buds may remain dormant or develop into aerial shoots or new rhizomes. Regeneration of single node fragments is mainly in March-May and October-November. Tubers germinate when separated from the rhizome system and can remain viable for long periods in soil. Tubers that remain attached to the parent rhizome do not germinate.
Persistence and Spread
The plant reproduces by spores that are readily wind dispersed but the importance of sexual reproduction is unclear. Numerous spores are released but they are very short-lived.
Vegetative reproduction via rhizomes and tubers is probably the most important means of spread and perennation. A 10 cm length of rhizome has been shown to produce a total of 64 m of rhizome in 1 year. It has been estimated that horsetail has the potential to infest an area of 1 hectare within 6 years of introduction. Tubers germinate when separated from the rhizome system and can remain viable for long periods in soil.
Horsetail is difficult to control by cultivation because new stems regenerate from rhizome fragments and from tubers. Black plastic sheeting has been found to kill or suppress rhizomes in the upper layers of soil however, the emerging vegetative stems can penetrate some woven polypropylene mulches. Horsetail can survive periods of flooding and burning but may be sensitive to water stress in drought conditions, especially in competition with other plants.
Control measures on arable land include soil drainage, liming, deep cultivation, improvements in soil texture and persistent cutting of vegetative and spore bearing shoots. In grass, regular mowing over a period of years may eliminate horsetail.
Horsetail is not very competitive in tall crops. The lack of functional leaves may make it intolerant of shading. Horsetail does not respond as quickly as cereals to increased soil fertility.
No effective biological control agents have been found.
Updated October 2007.