Urtica urens
(annual nettle)

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Identity

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Preferred Scientific Name

• Urtica urens L. 1753

Preferred Common Name

• annual nettle

Other Scientific Names

• Urtica minor Moench., 1802

International Common Names

• English: burning nettle; bush stinging nettle; dognettle; dwarf (stinging) nettle; nettle; small nettle; stinging nettle
• Spanish: ortiga; ortiga blanca; ortiga brava; ortiga chica; ortiga comum; ortiga menor; ortiga negra; ortiga romana; rupa chico
• French: ortie; ortie brulante; petite ortie
• Arabic: horreig; hurrayk; shar-el-aguz; zaghil
• Portuguese: urtiga menor

Local Common Names

• Brazil: urtiga
• Denmark: braende naelde; liden naelde
• Finland: rautanokkonen
• Germany: Kleine Brennessel; Kleine Nessel
• Iceland: brenninetla
• Italy: ortica minore; ortica piccola
• Japan: karafuto-irakusa
• Netherlands: kleine brandnetel
• Norway: smanesle; stornesle
• South Africa: bosbrandnetel
• Sweden: brannassala; etternaessla
• Turkey: isigan otu
• USA: burning nettle
• Yugoslavia (Serbia and Montenegro): sitna kopriva

EPPO code

• URTUR (Urtica urens)

Taxonomic Tree

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• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Urticales
•                         Family: Urticaceae
•                             Genus: Urtica
•                                 Species: Urtica urens

Notes on Taxonomy and Nomenclature

Top of page The name Urtica urens is universally accepted for this common, widespread weed (Hartley, 1979). There appears to have been virtually no revision of the taxonomic treatment or nomenclature of the species since it was described by Linnaeus in 1753. Plants are diploid and have a 2n chromosome number of 26 (Woodland et al., 1976).

Description

Top of page U. urens is an annual, growing up to 75 cm tall, branching at the base. It can be a particular nuisance because the bristles or hairs on its leaves and stems give off a substance that causes an intense burning sensation. Clusters of small, greenish-white flowers form where leaves join stems. The seed leaves are round or slightly elongated with smooth edges and a notch in the tip. First true leaves and all later leaves have distinctly toothed edges.

Distribution

Top of page U. urens is native to Europe, but now occurs in over 50 temperate countries or locations at high altitude.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Habitat

Top of page U. urens is adapted to many environments, infesting a wide range of horticultural crops, especially where there is irrigation or summer rainfall. In pastures, it can become prevalent in situations rich in organic material or manure, such as stock camps, holding yards or watering points (Lazarides et al., 1997).

Hosts/Species Affected

Top of page U. urens has been reported in many types of vegetable crops, orchards (citrus, pome and stone fruits) and vineyards. It is also a problem in nursery crops (conifers, ornamental shrubs, forest trees, fruit trees, roses, cut flowers) and gardens.

Host Plants and Other Plants Affected

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Biology and Ecology

Top of page U. urens is frequently found on light-textured soils, especially those rich in organic matter. It responds well to N and entire plants contain over 5% N.

Seed can remain viable for 20-100 years in the soil. Emergence is enhanced by soil disturbance and mostly occurs from within the top 2.5 cm of soil. Only 4% viable seed remained in the soil after 6 years of cultivation, compared with 39% viable seed in undisturbed soil (Holm et al., 1997).

Seed germination is optimal at 25°C and decreases rapidly at temperatures below 20°C (Andersen, 1968). Germination is greater in darkness than in light. Most seedlings appear in spring, but emergence continues through to mid-summer. Few plants emerge from late summer to early winter. Plants flower from late spring to autumn and are killed by frost.

U. urens is light-loving and dry matter distribution is not affected by light intensity. It is most competitive in full sunlight, whereas the perennial U. dioica is better adapted to shade (Corre, 1984). When drought-stressed, U. urens flowers several days earlier than normal and the number of nodes with inflorescences drops from eight to four per plant (Boot et al., 1986). Occasionally it flowers and sets seed when 8-10 cm tall and before the cotyledonary leaves have dropped off. Several successions of inflorescences are usually found on early emerging plants. Seeds formed early in the season may produce new plants in the same year.

Pollen release in the Urtica genus is unique. Immature stamens are bent towards the centre of the flower. When the anthers mature, the stamens suddenly straighten, shooting pollen into the wind. Plants are cross-pollinated and produce 100-1300 seeds weighing 0.5 mg each. Seeds are rich in oily endosperm and do not float on water (Holm et al., 1997).

Each stinging hair on U. urens is a tapered, elongated cell, constricted just below the tip, with a bulbous base embedded in the multicellular pedestal. When hit, the tip breaks off and the hair becomes a miniature hypodermic needle that penetrates the skin and injects its irritating chemicals. The tip of the hair is high in silica, but the silica concentration decreases towards the base, where it is replaced by calcium (Thurston and Lersten, 1969). Each hair is 100 µm long and has 10 µg of fluid that contains histamine and acetylcholine. Stem hairs have 2.5 times more acetylcholine than leaf hairs, whereas upper and lower surface leaf hairs have equal concentrations. The leaf itself has nearly as much histamine and acetylcholine as the leaf hairs. Crushed leaves can also give a stinging sensation, but are not as irritating as the hairs. The stinging reaction disappears within 1-3 hours for most people, but the hairs can remain in tissue and cause pain for 24-36 hours. Plants are not considered toxic to livestock, but cause the same irritating reaction in all animals (Everist, 1974).

Natural enemies

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Notes on Natural Enemies

Top of page Damage produced on U. urens in Argentina by the fungus Septoria urticae suggests that this organism is a potential biological control agent (Dal-Bello et al., 1993; 1995). Species of Pratylenchus nematodes were found in the roots of 31 weed species surveyed in Germany, with the highest infestations on U. urens (Rossner, 1983).

U. urens is susceptible to arabis mosaic nepovirus and hop mosaic carlavirus (Brunt et al., 1996).

Impact

Top of page Holm et al. (1997) rank U. urens amongst the 200 worst weeds of the world. As with most weeds, however, quantitative data on the economic impact of the species is extremely limited.

U. urens is a weed of 27 crops in 50 countries and is a frequently reported weed of vegetables and orchards (Holm et al., 1997). Once U. urens appears in vegetable fields, populations can increase rapidly. In locations where U. urens was one of the dominant weeds in unweeded potato crops in Egypt, tuber yield was reduced by 40% (Abusteit and Shehata, 1993). Where it was one of the dominant weeds of faba beans in Portugal, yield losses were 29-34% (Fernandes, 1989).

U. urens is included in a catalogue of problem plants in southern Africa (Wells et al., 1986), where its impacts are listed as competition, replacement of preferred vegetation (indigenous), skin irritation, seed contamination and obstruction of access.

In Morocco, U. urens is an alternative host for Leveillula taurica, the causal agent of tomato powdery mildew (Besri and Hormattallah, 1985). Carnation ringspot dianthovirus and tomato bushy stunt tombusvirus were found on apple, pear, cherry, sweet cherry and plum in East German orchards and were also isolated from U. urens (Kegler et al., 1983).

Uses

Top of page Herbal uses of U. urens have been known for centuries. Fresh plants have a painful, but beneficial effect on rheumatism. Leaves and flowers are reportedly powerful diuretics (Holm et al., 1997). In spite of the stinging hairs, young stems and leaves are edible and can be boiled as a green vegetable or in soup (Lazarides et al., 1997). Nettles have also been used to make beer and tea. According to Szabo et al. (1973), U. urens has a crude protein content of about 25% of dry matter. Zulu peoples in Africa regarded the plant as an aphrodisiac (Watt and Breyer-Brandwijk, 1932).

Leaf extracts of U. urens showed nematicidal properties against the citrus nematode, Tylenchulus semipenetrans (Mohammad et al., 1981).

Uses List

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Environmental

• Host of pest

Human food and beverage

• Vegetable

Materials

• Pesticide

Medicinal, pharmaceutical

• Traditional/folklore

Similarities to Other Species/Conditions

Top of page U. urens is rarely confused with related species. This is supported by the stability of its taxonomic treatment and nomenclature.

Prevention and Control

Top of page Cultural Control

Cultural control is effective, but handweeding is not recommended because of the plant's irritant properties (Whibley and Christensen, 1982). Selective mechanical weed control methods for several weeds, including U. urens, was investigated by Fogelberg and Gustavsson (1998). Emergence is enhanced by soil disturbance and the resultant seedlings can be controlled by follow-up cultivation or herbicides.

Vegetable cropping favours weed species which require only a comparatively short interval between emergence and the start of seed production, and whose seeds can germinate over a wide temperature range. Urtica urens is one of several weed species that can build up large seed banks during intensive vegetable production (Roberts, 1983).

U. urens is susceptible to control by flame-weeding (Ascard, 1995).

Chemical Control

Herbicide recommendations are available for most crops and situations where U. urens is a problem (Parsons, 1992), summarized below:

Asparagus: simazine
Aubergines, peppers: chlorthal-dimethyl
Beets: phenmedipham, chloridazon
Berry fruits: simazine
Brassica vegetables: chlorthal-dimethyl, metolachlor
Carrots: linuron, chlorthal-dimethyl, prometryn, propazine
Celery: prometryn
Cereals: linuron, oxyfluorfen (pre-sowing), glyphosate (pre-sowing), 2,4-DB, 2,4-D, MCPA, MCPB, metribuzin, methabenzthiazuron
Chickpeas, lentils, vetches: cyanazine
Citrus: simazine
Cotton: chlorthal-dimethyl
Faba beans (Vicia faba): metribuzin, cyanazine
Field peas: prometryn, metribuzin, cyanazine, methabenzthiazuron, MCPB
Garlic: chlorthal-dimethyl
Groundnuts: 2,4-DB
Hops: simazine
Legume vegetables: chlorthal-dimethyl, prometryn (beans, canning peas)
Lettuce: propyzamide
Linseed: MCPA
Lucerne: chlorthal-dimethyl, 2,4-DB, prometryn
Maize: linuron, MCPA
Onions: linuron, chlorthal-dimethyl, prometryn
Ornamentals: chlorthal-dimethyl, simazine (gladioli, roses)
Parsnips: linuron, propazine,
Pastures: dicamba/MCPA, prometryn, 2,4-DB, 2,4-D, MCPA, MCPB, methabenzthiazuron
Perennial grasses: chlorthal-dimethyl, prometyrn, methabenzthiazuron
Potatoes: linuron, chlorthal-dimethyl, prometryn, metribuzin
Sorghum: MCPA
Soyabeans: linuron
Stone fruits, pome fruits, grapevines: simazine, oxyfluorfen
Strawberries: phenmedipham, chlorthal-dimethyl
Sweet potatoes, yams: chlorthal-dimethyl
Tomatoes: metribuzin
Turfgrasses: chlorthal-dimethyl, MCPA

Non-crop areas: simazine, 2,4-D, imazapyr, glyphosate

Agamalian (1991) used N fertilizer solutions (liquid ammonium nitrate and ammonium thiosulfate) for selective control of broadleaved weeds resistant to soil-applied herbicides, including U. urens. Application of the N fertilizer solutions was most effective when weeds were at the 1-4-leaf stage.

Biological Control

Apart from the studies by Dal-Bello et al. (1993, 1995), there has been little consideration of the biological control of U. urens.

References

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Abusteit EO; Shehata SA, 1993. Critical period of weed competition in potatoes (Solanum tuberosum L.) summer plantation. Bulletin of Faculty of Agriculture, University of Cairo, 44(3):533-548

Agamalian HS, 1991. The utilization of nitrogen fertilizer solutions for selective weed control in crucifer crops. Proceedings of the Brighton Crop Protection Conference, Weeds, Vol. 2:605-610

Andersen RN, 1968. Germination and establishment of weeds for experimental purposes. Urbana, USA: Weed Science Society of America.

Asai Y, 1975. On a new naturalised weed, Urtica urens L. in Japan. Journal of Japanese Botany, 50(7):223

Ascard J, 1995. Effects of flame weeding on weed species at different developmental stages. Weed Research (Oxford), 35(5):397-411

Baker JG; 1877, reprint 1970. Flora of Mauritius and the Seychelles. Cramer, 125.

Battandier JA, 1888-90. Flore de L'Algerie. Algiers, Algeria: Libraire Adolphe Jourdan.

Bello GMdal; Perello AE; Monaco CI, 1993. Preliminary evaluation of Septoria urticae Rob. et Desm. as a biological control agent of Urtica urens L. Agronomie, 13(2):121-124

Besri M; Hormattallah A, 1985. Occurrence and survival of Leveillula taurica, cause of tomato powdery mildew in Morocco. Phytopathologische Zeitschrift, 112(4):348-354

Boot R; Raynal DJ; Grime JP, 1986. A comparative study of the influence of drought stress on flowering in Urtica dioica and U. urens. Journal of Ecology, 74(2):485-495

Britton NL, 1965. Flora of Bermuda. New York, USA: Harper Publishing Company.

Britton NL; Brown A, 1943. An illustrated flora of the Northern United States, Canada and the British Possessions. Lancaster, USA: Lancaster Press.

Brunt AA; Crabtree K; Dallwitz MJ; Gibbs AJ; Watson L (eds), 1996. Viruses of plants. Descriptions and lists from the VIDE database. Wallingford, UK: CAB INTERNATIONAL, 1484 pp.

Corre WJ, 1984. Growth and morphogenesis of sun and shade plants. IV. Competition between sun and shade plants in different light environments. Acta Botanica Neerlandica, 33(1):25-38

Dal Bello GM; Carranza MR, 1995. Weed diseases in La Plata area II. Identification of pathogens with potential for weed biocontrol programmes. Revista de la Facultad de Agronomi^acute~a (La Plata), 71(1):7-14; 21 ref.

Edgecombe WS, 1970. Weeds of Lebanon. Beirut, Lebanon: American University of Beirut.

Everist SL, 1974. Poisonous Plants of Australia. Sydney, Australia: Angus & Robertson.

Fernandes JD, 1989. Weed control in faba bean. Proceedings of the 4th EWRS symposium on weed problems in Mediterranean climates. Vol. 2. Problems of weed control in fruit, horticultural crops and rice. Wageningen, The Netherlands: EWRS, 83-88.

Flora of North America Editorial Committee, 1997. Flora of North America, Vol 3. New York, USA: Oxford University Press.

Fogelberg F; Gustavsson AMD, 1998. Resistance against uprooting in carrots (Daucus carota) and annual weeds: a basis for selective mechanical weed control. Weed Research (Oxford), 38(3):183-190; 34 ref.

George AS; ed, 1989. Flora of Australia, Vol 3. Canberra, Australia: Australian Government Printing Service.

Hartley W, 1979. A checklist of economic plants in Australia. Melbourne, Australia: CSIRO.

Haslam SM; Sell PD; Wolseley PA, 1977. A Flora of the Maltese Islands. Msida, Malta: Malta University Press.

Holm L; Doll J; Holm E; Pancho J; Herberger J, 1997. World Weeds. Natural Histories and Distribution. New York, USA: John Wiley and Sons, Inc.

Jessop J, 1981. Flora of Central Australia. Australia: Australian Systematic Botany Society, 41.

Kegler H; Kegler G; Kleinhempel H, 1983. Epidemiological investigations on carnation ringspot virus and tomato bushy stunt virus in fruit orchards. Zeszyty Problemowe Postepow Nauk Rolniczych, 291:155-162

Lazarides M; Cowley K; Hohnen P, 1997. CSIRO handbook of Australian weeds. CSIRO handbook of Australian weeds., vii + 264 pp.

Migahid AM, 1988. Flora of Saudi Arabia Vol. 1. 3rd edn. Riyadh, Saudi Arabia: King Saud University Libraries.

Mohammad HY; Husain SI; Al-Zarari AJ, 1981. Effect of plant extracts of some poisonous plants of Iraq on mortality of citrus nematode, Tylenchulus semipenetrans Cobb. Acta Botanica Indica, 9(2):198-200

Parsons JM(Editor), 1992. Australian weed control handbook. Melbourne, Australia; Inkata Press.

Polunin O, 1980. Flowers of Greece and the Balkans. Oxford, UK: Oxford University Press.

Prain D, 1917. Flora of Tropical Africa, Vol VI. London, UK: Lovell Reeve & Co Ltd.

Roberts HA, 1983. Weed seeds in horticultural soils. Scientific Horticulture, 34:1-11

Rossner J, 1983. Attack of weeds by nematodes of the genus Pratylenchus. Zeitschrift für Pflanzenkrankheiten und Pflanzenschutz, 90(1):22-27.

Szabo L; Horvath Z; Pinter I, 1973. Gene resources of the natural flora in Hungary. Agrobotanika, 15:57-80

Tawfik MFS; Awadallah KT; Shalaby FF, 1976. Survey of insects found on common weeds in Giza region, Egypt. Bulletin of the Entomological Society of Egypt, 60:7-14.

Thurston E; Lersten N, 1969. The morphology and toxicology of plant stinging hairs. Botanical Review, 35:393-412.

Tutin TG; Heywood VH; Burges NA; Valentine DH; Walters SM; Webb DA, 1964. Flora Europaea, Vol. 1. Cambridge, UK: Cambridge University Press.

Wagner WL; Herbst DR; Sohmer SH, 1990. Manual of Flowering Plants of Hawaii. Bernice Pauahi Bishop Museum Special Publication 83. Honolulu, Hawaii, USA: University of Hawaii.

Watt JM; Breyer-Brandwijk MG, 1962. The Medicinal and Poisonous Plants of Southern and Eastern Africa. Edinburgh and London, UK: E & S Livingstone Ltd.

Wells MJ; Balsinhas AA; Joffe H; Engelbrecht VM; Harding G; Stirton CH, 1986. A catalogue of problem plants in South Africa. Memoirs of the botanical survey of South Africa No 53. Pretoria, South Africa: Botanical Research Institute.

Whibley DJE; Christensen TJ, 1982. Garden Weeds: Identification and Control. Handbook 3. Adelaide, Australia: Adelaide Botanic Gardens.

Woodland DW; Bassett IJ; Crompton CW, 1976. The annual species of stinging nettle (Hesperocnide and Urtica) in North America. Canadian Journal of Botany, 54(3/4):374-383

Zohary M, 1962. Plant Life of Palestine. New York, USA: The Ronald Press Co.

Zohary M, 1966. Flora Palaestina. Part One. Jerusalem, Israel: The Israel Academy of Sciences and Humanities, 186.

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Distribution Maps

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