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21 November 2019

Polygonum nepalense (Nepal persicaria)

Datasheet Types: Pest, Invasive species, Host plant

Abstract

This datasheet on Polygonum nepalense covers Identity, Overview, Distribution, Hosts/Species Affected, Diagnosis, Biology & Ecology, Natural Enemies, Impacts, Uses, Prevention/Control, Further Information.

Identity

Preferred Scientific Name
Polygonum nepalense Meisner (1826)
Preferred Common Name
Nepal persicaria
Other Scientific Names
Persicaria nepalensis (Meisner) H. Gross
Polygonum alatum Sprengel (1827)
Polygonum lyratum Nakai
Polygonum punctatum var. alatum Buch.-Ham. ex D.Don (1825)
Polygonum quadrifidum Hayata
International Common Names
English
snake weed (India)
Local Common Names
Bhutan
berkhey ratnaulo
helepsi
metoshim
shido
Ethiopia
labuche
Germany
Nepalesischer Koeterich
Indonesia
asem tembagan
ganrot
hahaseuman
jukut asam
Japan
tanisoba
Sri Lanka
kangany-machan-pillu
EPPO code
POLAL (Polygonum alatum)
EPPO code
POLNE (Polygonum nepalense)

Pictures

Polygonum nepalense (Nepal persicaria); Flowering habit. Table Land, Panchgani, India. August 2010.
Flowering habit
Polygonum nepalense (Nepal persicaria); Flowering habit. Table Land, Panchgani, India. August 2010.
©Dinesh Valke/via Flickr - CC BY-SA 2.0
Polygonum nepalense (Nepal persicaria); Flowers and foliage. Table Land, Panchgani, India. August 2010.
Flowers and foliage
Polygonum nepalense (Nepal persicaria); Flowers and foliage. Table Land, Panchgani, India. August 2010.
©Dinesh Valke/via Flickr - CC BY-SA 2.0
Polygonum nepalense (Nepal persicaria); Flowers and foliage. Table Land, Panchgani, India. August 2010.
Flowers and foliage
Polygonum nepalense (Nepal persicaria); Flowers and foliage. Table Land, Panchgani, India. August 2010.
©Dinesh Valke/via Flickr - CC BY-SA 2.0
Polygonum nepalense (Nepal persicaria); Flowers and foliage. Table Land, Panchgani, India. August 2010.
Flowers and foliage
Polygonum nepalense (Nepal persicaria); Flowers and foliage. Table Land, Panchgani, India. August 2010.
©Dinesh Valke/via Flickr - CC BY-SA 2.0
Polygonum nepalense (Nepal persicaria); Flowers and foliage. Table Land, Panchgani, India. August 2010.
Flowers and foliage
Polygonum nepalense (Nepal persicaria); Flowers and foliage. Table Land, Panchgani, India. August 2010.
©Dinesh Valke/via Flickr - CC BY-SA 2.0
Polygonum nepalense (Nepal persicaria); Flowers. Anserma, Colombia. June 2010.
Flowers
Polygonum nepalense (Nepal persicaria); Flowers. Anserma, Colombia. June 2010.
©Hugo Vargas/via Wikimedia Commons - CC BY-SA 4.0

Taxonomic Tree

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Notes on Taxonomy and Nomenclature

Hutchinson et al. (1954) give P. punctatum var. alatum as a synonym (together with P. alatum), while the P. punctatum Buch.-Ham. in southern India, illustrated by Tadulingam et al. (1955), is apparently the same species. P. punctatum Ell., however, is a quite distinct temperate species (Hafliger and Wolf, 1988). Many Polygonum species, including P. nepalense and P. lapathifolium have recently been re-named as Persicaria species. Hence some modern floras, including Flora of Bhutan (Grierson and Long, 1983), use the name Persicaria nepalensis (Meisner) H. Gross. However, the more familiar older name is retained for the purposes of this Compendium.

Description

P. nepalense is an annual plant, prostrate to sub-erect, stems simple or branched 15-30(-45) cm high. Leaves are alternate, ovate to elliptic, up to 5 cm long, often with a pair of dark blotches each side of the mid-rib. The lamina is characteristically decurrent, causing the petiole to be effectively winged, and usually auriculate at the base. Foliage is generally glabrous, but punctate with scattered yellow glands on the underside. Ochreae are truncate, 6-10 mm long, sparsely pubescent. The individual flowers, 2-3 mm long, are usually pink, but sometimes white, with four perianth segments. They are carried in dense round clusters up to 1 cm in diameter, sessile or on peduncles up to 5 cm long, singly, or several subtended in upper leaf axils. Seeds are about 2 mm long, trigonous or biconvex, strongly pitted, black.This description is based largely on Grierson and Long (1983). Everaarts (1981) has especially good drawings.

Distribution

P. nepalense is believed to have originated in the Himalayas but it is now quite widespread, across the Asian, African and American continents and in the Pacific, but is apparently limited, as a significant weed, to high altitude tropics. Why it does not occur more commonly in temperate lowlands, which have roughly comparable temperature regimes is not clear. It can persist sporadically, in temperate regions, even as far north as the UK but is not reported as a weed problem.

Distribution Map

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Distribution Table

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Hosts/Species Affected

P. nepalense appears to have particular climatic requirements, being very much restricted to high altitude tropics, but within this ecology, it occurs in many, if not most of the crops grown. It is especially abundant in tea, both in India and in East Africa, perhaps encouraged by the repeated use of minimal doses of paraquat which do not provide complete control. It can, however, be predominant in other crops in the absence of any herbicide use. Everaarts (1981) notes that it is one of the commonest weeds of vegetables in highland Java, Indonesia.

Host Plants and Other Plants Affected

HostFamilyHost statusReferences
Brassica napus var. napus (rape)BrassicaceaeOther 
Camellia sinensis (tea)TheaceaeMain 
Daucus carota (carrot)ApiaceaeOther 
Eragrostis tef (teff)PoaceaeOther 
Hordeum vulgare (barley)PoaceaeMain 
Oryza sativa (rice)PoaceaeOther 
Solanum tuberosum (potato)SolanaceaeMain 
Triticum aestivum (wheat)PoaceaeMain 
Vicia villosa (hairy vetch)FabaceaeOther 
Zea mays (maize)PoaceaeMain 

Similarities to Other Species/Conditions

Although there are many related Persicaria and Polygonum species occurring as weeds, none are likely to be confused with P. nepalense, due to the latter's distinctive leaf shape. The one exception in Bhutan and perhaps elsewhere in the Himalayas is P. runcinata [ Polygonum runcinatum] which has a similar inflorescence, and sometimes has a somewhat similar leaf shape, but is perennial, with leaves that are normally 'runcinate' with distinct lobes.

Habitat

P. nepalense has seemingly strict environmental requirements, being largely restricted to the high altitude tropics, from 750-3000 m in Bhutan (Grierson and Long, 1983); 1200-2500 m in southern India (Tadulingam et al., 1955); 1400-2900 m in Ethiopia (Stroud and Parker, 1989) and 1500-2500 m in East Africa (Ivens, 1968). It might be expected to occur also at lower altitudes in temperate areas, but this is rarely so. Where it is common it occurs in a range of disturbed situations, mainly as a weed of annual and perennial crops, around field edges, in the open or in partial shade, usually in moist conditions.

Biology and Ecology

P. nepalense is a relatively short-lived annual, completing development within 4-5 months, though this short period is perhaps partly due to attack by Puccinia polygoni-amphibii (Eden and Bond, 1925). Reproduction is solely by seeds which are produced in great abundance. Eden and Bond (1925) recorded over 30 million seeds/ha, often resulting in complete dominance under suitable conditions in, for example, the highlands of Sri Lanka, southern India and the Himalayas. The reason for its virtual restriction to these highland situations is unexplained. There are no reports of studies on germination behaviour, other than one from Japan indicating 50% viability maintained after 4.5 years storage in soil at 15 cm depth (Watanabe, 1978).Eden and Bond (1925) indicate that P. nepalense is 'not particularly tolerant of shade' but its predominance in tea must suggest that it has some shade tolerance. The same authors studied the balance between P. nepalense and other weeds under different fertilizer regimes and showed that this species has a lower optimum phosphate level, and that addition of high phosphorus levels encouraged other weeds more and reduced the dominance of P. nepalense.Everaarts (1981) indicates that P. nepalense prefers not too dry soils in open or lightly shaded situations and is favoured by high soil fertility.

List of Pests

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Natural enemies

Natural enemyTypeLife stagesSpecificityReferencesBiological control inBiological control on
Puccinia polygoni-amphibiiPathogen     
Ustilago polygoni-alatiPathogen     

Impact

P. nepalense is a weed which apparently only thrives in high altitude tropics but in these areas can become dominant. It is listed by Holm et al. (1979) as a 'principal' or 'serious' weed in Ethiopia, Sri Lanka and India. It is noted as being one of the six most prominent weeds of potato in the Nilgiri Hills of southern India (Nimje, 1988), one of the most important weeds of maize and potato in the 'dry subtropical' and warm and cool temperate zones between 1200 and 2400 m in Bhutan (Parker, 1992) and one of the three most aggressive weeds of wheat in Ethiopia (Gebre et al., 1987). Comparably, in Colombia, it was one of the predominant weeds of carrot on the altiplano de Pasto (Mena et al., 1984). In Indonesia, Everaarts (1981) refers to it as 'one of the commonest and troublesome weeds' of vegetables in highland Java at 1100-2300 m.There are no reports on the competitive effect of P. nepalense and it has sometimes been regarded as relatively non-competitive in tea, to the point that it may be encouraged as a ground cover to suppress other, more serious, weeds (see Uses), but there can be little doubt that the dense infestations that can occur under suitable conditions must be competing significantly for nutrients.

Uses

In Sri Lanka, P. nepalense has been regarded as a valuable ground cover, protecting soil from erosion (Eden and Bond, 1925). Weeding methods were deliberately aimed at encouraging P. nepalense in preference to other more troublesome species. It is not known whether this is still practiced, though in 1951, Haigh commented that P. nepalense was 'a very good cover for tea above 1000 m', only needing to be removed from around the base of bushes.

Uses List

Environmental > Erosion control or dune stabilization

Prevention and Control

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Cultural Control

P. nepalense is shallow-rooted and readily removed by manual or hoe weeding.

Chemical Control

Recent information on the response of P. nepalense to herbicides is sparse. Older reports from Ethiopia show that it is susceptible to many of the standard herbicides for control of broad-leaved weeds, including MCPA, 2,4-D, dicamba, ioxynil, bromoxynil, fluorodifen, ametryne and prometryne (CADU, 1975; Anon., 1978). It is susceptible to terbutryne and methabenzthiazuron post-emergence, but possibly not pre-emergence. It was not controlled by bentazon. It is controlled by full doses of paraquat but may be relatively favoured by the use of reduced doses.

References

Eden T, Bond TET, 1925. The effect of manurial treatments on the growth of weeds in tea. Empire Journal of Experimental Agriculture, 13:141-157.
Ethiopia, Arssi Rural Development Unit, Crop and Pasture Section, 1978. Report on crop protection surveys and experiments 1976/77. Report on crop protection surveys and experiments 1976/77. P.O. Box 3376, Addis Ababa. Ethiopia, 75 pp.
Ethiopia, Chilalo Agricultural Development Unit, 1975. Crop protection activities, 1974. Parts from report on surveys and experiments carried out in 1974 by Crop and Pasture Section. Crop protection activities, 1974. Parts from report on surveys and experiments carried out in 1974 by Crop and Pasture Section. CADU. Asella Ethiopia, CADU Publication No. 111:147-195
Everaarts AP, 1981. Weeds of vegetables in the highlands of Java. Weeds of vegetables in the highlands of Java. Horticultural Research Institute. Pasarminggu, Jakarta Indonesia, 121 pp.
Gebre H, Tarekegne A, Asmare E, 1987. Preliminary indications on the importance of yield limiting factors on wheat. Fifth Regional Wheat Workshop for Eastern, Central and Southern Africa and the Indian Ocean. Mexico City, Mexico: CIMMYT, 189-193
Grierson AJC, Long DG, 1983. Flora of Bhutan, Volume 1, Part 1. Edinburgh, UK: Royal Botanic Garden.
Guo L, 1993. Ustilago deyeuxiae sp.nov. and three smut species new to China. Mycosystema, 6:51-55
Hafliger TJ, Wolf M, 1988. Dicot Weeds. 1. Basle, Switzerland: CIBA-GEIGY Ltd.
Haigh JC, 1951. A Manual of the Weeds of the Major Crops of Ceylon. Peradenya Manual No. 7. Colombo, Sri Lanka: Department of Agriculture.
Henty EE, Pritchard GH, 1975. Weeds of New Guinea and their Control. Lp, Papua New Guinea: Department of Forests, Division of Botany, Botany Bulletin No.7.
Holm LG, Pancho JV, Herberger JP, Plucknett DL, 1979. A geographical atlas of world weeds. New York, USA: John Wiley and Sons, 391 pp.
Hutchinson J, Dalziel JM, Keay RWJ, 1954. Flora of West Tropical Africa. Volume 1, Part 1, 2nd edition. London, UK: Crown Agents.
Ivens GW, 1967. East African Weeds and their Control. Nairobi, Kenya: Oxford University Press.
Kaul MK, 1986. Weed Flora of Kashmir Valley. Jodhpur, India: Scientific Publishers, 422 pp.
Mena F, Madronero E, Salcedo-Z A, Criollo-E H, 1984. A study of the critical period of competition between weeds and carrot (Daucus carota L.) crops on the Pasto plateau, Narino Department. Revista de Ciencias Agricolas, 8(1/14):114-120
Nimje, 1988. Weed survey of potato fields of the higher hills of Nilgiris. Indian Journal of Weed Science, 20(4):26-31
Numata M, Yoshizawa N, 1975. Weed flora of Japan. Japan Association for the Advancement of Phyto-Regulators. Tokyo, Japan: Zenkoku Noson Kyoiku Kyokai.
Parker C, 1992. Weeds of Bhutan. Weeds of Bhutan., vi + 236 pp.
Reed CF, 1977. Economically important foreign weeds. Potential problems in the United States. Agriculture Handbook No. 498. United States Department of Agriculture. Washington D.C., USA: USDA-ARS.
Stace C, 1991. New Flora of the British Isles. Cambridge, UK: Cambridge University Press.
Stroud A, Parker C, 1989. A Weed Identification Guide for Ethiopia. Rome, Italy: Food and Agriculture Organization.
Tadulingam C, Venkatanarayana G, Mudaliar CR, Sakharam Rao J, 1955. A Handbook of some South Indian Weeds. Second edition. Madras, India: Madras Government Press.
Vibrans H, Hanan Alipi AM, 2008. Notes on neophytes 4. Polygonum nepalense (Polygonaceae), an invasive plant new for Mexico. (Notas sobre neófitas. 4. Polygonum nepalense (Polygonaceae), una planta invasora nueva para México.) Acta Botanica Mexicana, No.82:1-6. http://www.ecologia.edu.mx/publicaciones/ABM.htm
Wang ZR, 1990. Farmland Weeds in China. Beijing, China: Agricultural Publishing House.
Watanabe Y, 1978. Physiological and ecological studies on upland weeds in Hokkaido. Research Bulletin of the Hokkaido National Agricultural Experiment Station, No. 123:17-77
Webb DA, Chater AO, Akeroyd JR, 1993. Polygonum L. In: Tutin TG, Burges NA, Chater AO, Edmondson JR, Heywood VH, Moore DM, Valentine DH, Walters SM, Webb DA, eds. Flora Europaea Volume 1 Psilotaceae to Platanaceae 2nd edition. Cambridge, UK: Cambridge University Press, 91-97.
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.

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Published online: 21 November 2019

Language

English

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CABI
CABI Head Office, Wallingford, UK

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