field horsetail

Equisetum arvense is a perennial herbaceous plant that spreads by means of an underground rhizome. The slender, felted rhizome freely forks and bears stem tubers. The species is dimorphic, that is, it exhibits two distinct growth forms, both arising from the same rhizome. Fertile spore-bearing stems begin to appear in April. After shedding its spores, a fertile stem promptly withers and dies. Sterile green stems appear around the same time but last throughout the summer until the first frosts of autumn. The erect or prostrate sterile stems are 10–90 cm (3.9–35.4 in) tall and 3–5 mm (0.12–0.20 in) diameter, with jointed segments around 2–5 cm (0.79–1.97 in) long with whorls of side shoots at the segment joints; the side shoots have a diameter of about 1 mm (0.039 in). Some stems can have as many as 20 segments. The solid and simple branches are ascending or spreading, with sheaths that bear attenuate teeth. The off-white fertile stems are of a succulent texture, 10–25 cm (3.9–9.8 in) tall and 3–5 mm (0.12–0.20 in) diameter, with 4–8 whorls of brown scale leaves and an apical brown spore cone. The cone is 10–40 mm (0.39–1.57 in) long and 4–9 mm (0.16–0.35 in) broad. The fertile stems are typically precocious and appear in early spring. It has changed little from its ancestors of the Carboniferous period. E. arvense is a nonflowering plant, multiplying through spores. …

Equisetum arvense grows in a wide range of conditions, in temperatures less than 5 °C (41 °F) to greater than 20 °C (68 °F) and in areas that receive annual rainfall as low as 100 mm (3.9 in) and as great as 2,000 mm (79 in). It commonly occurs in damp and open woodlands, pastures, arable lands, roadsides, disturbed areas, and near the edge of streams. It prefers neutral or slightly basic clay loams that are sandy or silty, especially where the water table is high, though it can occur occasionally on slightly acid soils. The plant is widespread in the Northern Hemisphere, growing as far as 83° North in North America and 71° North in Norway, Sweden, Finland, and Russia and as far south as Texas, India and Iran. It is less widespread in the Southern Hemisphere, but it occurs in Argentina, Brazil, Chile, Madagascar, Indonesia, and Australia. It was introduced into New Zealand in the 1920s where it was identified as an invasive species by Ella Orr Campbell in 1949. It is listed on the National Pest Plant Accord, prohibiting its sale, spread and cultivation.

The plant contains several substances that can be used medicinally. It is rich in silicon (2-3%), potassium, calcium, manganese, magnesium and phosphorus, phytosterols, dietary fiber, vitamins A, E and C, tannins, alkaloids, saponins, flavonoids, glycosides and caffeic acid phenolic ester. The buds are eaten as a vegetable in Japan and Korea in spring. All other Equisetum species are toxic. In polluted conditions, it may synthesize nicotine. Recent research has shown limited evidence of anti-inflammatory, diuretic, antimicrobial, and antioxidant properties.

In horticulture and agriculture, an aqueous extract of E. arvense has been approved for use as a fungicide in the European Union and the United Kingdom (since Brexit). Horsetail extract can be used to prevent fungal pathogens on crops including:

Damping off (Pythium) and powdery mildew on cucumbers. Various fungal diseases of fruit trees, including scab (Venturia inaequalis), mildew, and peach leaf curl (Taphrina deformans). Both downy and powdery mildew on grapevines. Early blight (Alternaria solani) and Septoria blight (Septoria lycopersici) on tomatoes. Grey mould, powdery mildew, red core, and anthracnose fruit rot (Colletotrichum acutatum) in strawberries. Early blight, late blight, and powdery mildew on potatoes. Equisetum is used in biodynamic farming (preparation BD 508) in particular to reduce the effects of excessive water around plants (such as fungal growth). The high silica content of the plant reduces the impact of moisture.