Polygonum is from the Greek polys meaning many and gony meaning knee and refers to the many nodes on the stems.
Wireweed refers to the wiry stems of this weed.
Other names:
Hogweed
Knotweed
Prostrate Knotweed.
Summary:
Wireweed is a hairless, ground-hugging or sprawling, annual or perennial herb with small oval leaves usually 5-12 mm long. At the base of each leaf is a white to silvery sheath around the stem. In the leaf axils there are small clusters of pink-tinged flowers 2-3 mm long. Each flower is 5-lobed and has 7 or 8 stamens and 3 styles. The fruits are small, 3-angled and enclosed in the withered flower. The stems are slender, up to 1 m long, wiry and many branched.
Native to Europe, Wireweed is a common weed of pastures, roadsides and waste land. Flowering occurs in autumn and spring.
Description:
Cotyledons:
Two. Spear shaped, 10-15 mm long with a very short or no stalk. Tip pointed. Sides parallel. Base tapered. Surface hairless. Very young plants look like fine grass. The seedling has a long hypocotyl and an epicotyl.
First leaves:
The leaves grow singly and are spear shaped with a pointed tip, 10-15 mm long on a short stalk. Hairless. A membranous sheath surrounds the base of the leaf and stem. Later leaves are similar but larger.
Leaves:
Alternate. It does not form a rosette. Leaves usually fall off with age.
Stipules - (Ochrea) Long, membranous to thinly papery, later splitting into ragged fibres with age, silvery to white. Translucent at least near the top.
Petiole - Short.
Blade - Oblong to oval, 10-50 mm long by 4-12 mm wide, dull green to blue/green, tip pointed. Sides convex. Base tapered. Surface hairless. Side veins obvious on the under side. Later leaves and those on side branches are usually smaller.
Stems:
Prostrate (occasionally ascending), sprawling, up to 1000 mm long, wiry, stiff, solid, round or fluted with lengthwise grooves. Many branches at the base and along their length. Hairless. May form dense mats. Often reddish.
Flower head:
Single or in clusters of 1-5 in leaf axils on short stalks.
Flowers:
White or pink, 2 mm diameter, 2.1-2.7 mm long with a translucent membrane(ochreola) underneath.
Perianth - Tubular with 5 lobes split to below the middle. Lobes green with white or pink edges. Outer lobes curved inwards. Inner lobes flat, with wide overlapping edges.
'Petals' - 5, green with white or pink edges.
Stamens - 5-8, usually 7-8. Filaments swollen at the base. 3 short styles. 3 stigmas.
Anthers -
Fruit:
Nut. Triangular pyramid, dull brown to reddish black with dots and streaks, finely granular, 2-2.5 mm long. Usually inside the persistent flower parts. Fruit dimension and shape are used to determine separate different subspecies and varieties 655.
Seeds:
Enclosed in the nut. Tear shaped and ridged or angular. Surface shiny. About 1 mm diameter. Usually produces less than 50 seeds/plant 656.
Roots:
Strong, deep, tough, fibrous taproot.
Non-mycorrhizal 657.
Key Characters:
Stems long and wiry, glabrous, usually prostrate.
Leaves glabrous, 10-40 mm long, narrowly elliptic, main stem leaves much larger than those on lateral branches.
Stipular sheaths (ochrea) thinly scarious, later splitting into fibres, silvery translucent.
Flowers 1-5 in axillary clusters.
Floral whorl divided to below the middle.
Nut trigonous, tuberculate.
Annual.
655 has a list of 16 morphological characters for distinguishing ecotypes.
Biology:
Life cycle:
Annual or biennial. Seed germinates from autumn to early summer. Growth is rapid in warm weather. Flowers in spring to summer.
In Tasmania, plants that germinate in spring have stem leaves which are 30-50 mm long and dull green whilst those germinating later or in infertile areas have smaller leaves 15-30 mm long and are a darker green or blue green.
There is considerable variation and plasticity in phenotypes 658.
Physiology:
Tolerates heavy metals better than many plants and grasses 659.
Canola and lucerne stimulate wireweed 660.
Tolerant to flooding 661.
662 has chemical composition.
Reproduction:
By seed.
Flowering times:
Late spring to autumn in western NSW.
November to May in SA.
Probably November to March in Perth.
Summer in WA.
Seed Biology and Germination:
Sets large amounts of seed.
Germinates from autumn to spring 5.
Seed is initially dormant and requires cold stratification which makes it light sensitive, so, cold followed by light required for early germination 663. Temperature is a major factor in determining dormancy 664. Saline condition can induce dormancy and nearly 100% germination after 5/15 deg C stratification 665.
Fresh seed has maximum germination of 10% with best conditions (alternating temperatures and diurnal light). 4 deg C for 10 weeks on moist seed increased germination to 50% but sill required light for good germination 666.
Darkness or burial inhibits germination 667.
668 has a model for emergence by depth.
669 has a model of emergence taking into account seed bed preparation.
Buried seeds had a greater viability than surface seeds after one year and seeds on the surface had a higher germination level on the surface 670671.
Less than 1% of buried seed survives for more than 10 years in the soil in Alaska 672 or 5 years in the UK 673.
The highest seed set and lowest competition effect of wireweed in wheat occurred at 120 kg N/ha 674.
It tends to have high seed bank levels. 675 has seed bank levels for NSW, 676 for Bulgaria, 677 for the Balkans and 678 for Scotland.
Seed banks tend to build up under cereal cropping 679.
Passes through sheep gut unaffected but looses viability with time fermenting in the dung heap 680.
Late rains in SA lead to wireweed germination 5.
Vegetative Propagules:
None.
Hybrids:
Plants are usually hexaploid (2n=60) or less commonly tetraploid (2n=40) which gives wide ecological adaptation 681, 682.
Several forms occur that range from stress-tolerant waste land types to highly competitive cropland types 683.
Allelopathy:
Aqueous extracts inhibit the germination of lettuce and rice seeds 684 and lucerne seeds 685, 686.
Contains fatty acids that inhibit grass growth and some N fixing Azotobacter and Rhizobium 687.
Allelopathic to cotton, fat hen and several grasses but not Sporobolus 688 and displaces Bermuda grass (Couch) 689.
Affects rate of germination of medic and lettuce and causes deformed medic seedlings and probably responsible for poor medic establishment in SA 690.
Population Dynamics and Dispersal:
Spread by seed.
Carabid and other invertebrates take seed 691.
Spread in irrigation water at about 1 seed /m2 in Santiago, USA 692.
Origin and History:
Cosmopolitan. Europe.
Distribution:
ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
Occurs throughout Tasmania.
Argentina 693694695, Belgium 655, Chile 696, England 697, Finland 698, New Zealand 699, Pakistan 700, Poland 701702, Portugal 130130181, Scotland 703, 704678, Spain 705, 706.
Habitats:
Climate:
Temperate. Mediterranean.
Soil:
Prefers loams and heavy alkaline soils.
Occurs on a wide range of soils.
It can tolerate a wide soil pH range from 5.6 to 8.4 707.
Rarely occurs under Bracken but soon invades once Bracken is cleared 708.
Significance:
Beneficial:
Fodder, young plants are palatable, older plants are ignored until feed is scarce.
Honey. Used as a ground cover in areas where grass lawn is not suitable 659.
Used as a medicinal herb 709710 and acts as a vasorelaxant 711, hepatoprotective agent 712, anti-coccidial 713, anti-inflammatory agent inhibiting prostaglandin synthesis and platelet activity factor induced exocytosis 714, antipyretic, antiparasitic and diuretic 715.
Produces indigo like dye.
Resistant to root knot nematode and other nematodes 716.
Useful rehabilitation species in areas affected by heavy metals.
Detrimental:
Weed of crops causing yield reductions. The long wiry stems tangle in cultivators and occasionally it interferes with harvesters 717 especially in low or swathed crops. Competitive in young crops but most soon overgrow it. Competes for nutrients especially in conventional tillage systems 718.
Peas are sensitive to competition from wireweed 719.
Seeds may cause cereal grain contamination 720721.
Consuming large quantities of seed may cause enteritis.
May contain toxic nitrate levels. Horses eating wireweed in a hot dry period in NSW have died from nitrite/nitrate poisoning 730.
Legislation:
None.
Management and Control:
Conventional tillage favours wireweed more than no tillage planting systems 731 however 679 reports increased levels of wireweed in surveys of minimum tilled paddocks and 732 reports that shallow cultivation reduces wireweed in continuous winter wheat.
In SA, cultivating from February to June favoured wireweed 5.
Harrowing at emergence of peas is useful where herbicides can't be used 733.
Levels of wireweed increased following limitations on atrazine use in the US 734 and France 735
Ploughing provides better control than soil solarisation 731 but 736 using black plastic rather than clear film got good control.
Planting date doesn't have a big effect on infestation 737.
Tends to build up in cereal crops 679738.
Geese are ineffective for wireweed control and lead to greater infestations 739.
Spring tined weeders and brush-hoes were ineffective when wireweed was 1-9% ground cover 740.
Herbicides in combination with tillage gave more reliable control than herbicides alone 741.
In Australian summer fallows 1.5 L/ha 2,4-D amine500 plus 500 mL/ha dicamba or 1 L/ha 2,4-D ester800 gave better control than 600 mL/ha glyphosate450 plus 7 g/ha metsulfuron600 or 600 mL/ha glyphosate450 plus 400 mL/ha 2,4-D ester800 742.
Diflufenican provides long lasting pre-emergence control 743.
Thresholds:
High numbers required to affect wheat yields 744 especially in winter crops because of it normally has somewhat delayed emergence.
In common beans the greatest effect on yield occurs in the 28 days following planting 745.
For newly sown lucerne/fescue pasture there is a 3% decrease in lucerne and fescue establishment for each 10 g wireweed DM/m2 and 4% reduction in pasture production 746.
Fertiliser application has little effect on competitiveness and the main period of competition is from 20-40 days after planting in Argentina 747.
Critical period for competition with common bean is the first 60 days after planting 748.
Eradication strategies:
Cultivate before flowering. Manual removal is usually difficult because plants tend to grow in heavy soil and break off at the base and regrow. Use a weed fork to extract the taproot if removing manually.
In agricultural situations, glyphosate, dicamba and sulfonyl urea herbicides provide good control post-emergence and trifluralin, pendimethalin and sulfonyl ureas provide good pre-emergence control.
In bushland areas, wipe actively growing plants with a mixture of 1 L glyphosate(450g/L) plus 2 L water. For small areas, apply a mixture of 0.2 g metsulfuron(600g/kg) plus 100 mL Tordon®75-D to actively growing plants before flowering in spring or summer depending on when the Wireweed has germinated. On larger areas, Spinnaker® at 1 L/ha, or 20 mL per 10 L water for hand spraying, will provide reasonably selective control of small actively growing Wireweed and control seedlings for about a year. 5-10 g/ha of metsulfuron(600g/kg) or 0.2 g plus 25 mL wetting agent in 10 L water also provides good control. Inspect 3 times a year for several years.
For broadacre spraying before transplanting trees, 1 L/ha glyphosate plus 500 mL/ha 2,4-D ester(800g/L) plus 1 kg/ha simazine(900g/kg) plus 1 L/ha Dual®Gold plus 1% spray oil will control seedlings in spring and reduce summer establishments.
Herbicide resistance:
No resistance reported in Australia. Amitrole 749 and atrazine750 resistance reported from overseas 751, .
Biological Control:
Rutherglen bug feeds on the seed 62, 752.
Gastrophysa viridula causes variable but often heavy damage to wireweed in the USA 753.
Knotweed leaf beetle (Gastroidea polygoni) causes significant damage in Europe 754, 755 and Russia as both the larvae and adult 756.
Insects on wireweed host pathogens of Colorado potato beetle 757.
Related plants:
Black Bindweed (Polygonum convolvulus)
Creeping Knotweed (Polygonum prostratum)
Pale Knotweed (Polygonum lapathifolium, Polygonum lanigerum)
Princes Feather (Polygonum orientale)
Sand Wireweed (Polygonum arenastrum) is similar with smaller leaves, 5-20 mm long which are all of similar size on the same plant rather than the later leaves being smaller as in Wireweed.
Tree Hogweed (Polygonum patulum) has a much longer cotyledon and larger leaves, ochrea, flowers, and seeds.
Vietnamese mint (Polygonum odoratum)
Water Pepper (Polygonum hydropiper)
Polygonum capitatum
Polygonum glabrum
Plants of similar appearance:
Ribwort (Plantago lanceolata) is very similar as a seedling. Its cotyledon is narrower and longer, its first leaf is usually hairy and has a well defined median groove, lengthwise veins and has no sheathing membrane at the base of the leaf.
Bucks Horn Plantain (Plantago coronopus) is similar as a seedling until it produces its lobed, later, leaves. It also lacks the sheathing membrane (ochrea) at the base of the leaf.
References:
Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P206. Photo.
Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P283. Diagram.
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P153.
Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P231. Photo.
Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney). P582.
Gilbey, D. (1989). Identification of weeds in cereal and legume crops. Bulletin 4107. (Western Australian Department of Agriculture , Perth). P66. Photos.
Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia. (Plant Protection Society of Western Australia, Perth, Western Australia). P199. Photo.
Hyde-Wyatt, B.H. and Morris, D.I. (1975). Tasmanian weed handbook. (Tasmanian Department of Agriculture, Hobart, Tasmania). P50-51. Diagrams.
Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).
Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #1002.2.
Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P113.