Weed of the Week: Knotweed

Laurence Gale MScin Consultancy

Weed of the Week: Knotweed (postrate) Polygonum aviculare L.

By Laurence Gale MSc


What is a weed? By definition a weed is a plant that is growing in the wrong place. Weeds take valuable space, water, sunlight and nutrients that may otherwise be accessible to important crops, in our case turf grasses. Weeds not only compete for these resources they can disfigure and cause problems to playing surfaces.

Weeds are very good competitors and take advantage of any opportunities to colonise turf situations, particularly when the sward is under stress and weak, leaving bare soil areas for weeds to populate. Weeds have many mechanisms and characteristics that enable them to do this, having thick waxy cuticle leaves that can be resistant to some chemicals, fast reproduction methods, the ability to reseed in 6 week cycles and deep tap roots enabling the weed to survive in compacted dry ground conditions.

Weeds have one of three life cycles: annual; biennial or perennial.

  • Annual weeds: Live for a single season. These weeds germinate from seed in the spring or summer, flower and then die.

  • Biennial weeds: Live for two seasons. During the first growing season, these weeds remain in a vegetative stage and, in the following year, produce flowers, set seed and die.

  • Perennial weeds: Live for multiple seasons and flower more than once. Perennial structures (rhizomes, stolons, crowns, entire plants or roots) survive from year to year.

Some weeds may be harmful to the environment or noxious to your regional ecology. For example Japanese Knot weed (Fallopia Japonica) is fast becoming a major weed problem on road side verges and urban landscape areas, a very difficult weed to eradicate. It is very important to recognise weeds and seek effective controls methods to eradicate them from our facilities.

Weeds can also be used as an indicator of soil conditions. For example, knotweed and plantains both indicate soil compaction because they can maintain adequate root respiration at lower oxygen diffusion levels than other plants. Different weeds tolerate different soil conditions, some are alkaline loving and others acid loving. Getting to understand and recognise the physiology of these plants will help you become better turfgrass managers.

This weeks weed is: Knotweed Polygonum aviculare L.

Scientific name


Life cycle

Polygonum aviculare L.



Form / Appearance

Knotweed is a weed mainly found in paddocks and pastures and, occasionally, pavements, roadsides, gardens and lawns. It has a prostrate form of growth, especially in close mown turf. Stems are very long and nodal with leaves forming alternately along the stem. Height: 10-60 cm.



Roots are fibrous and shallow.


Prostrate stems can grow up to 1 metre in length. Stems often sprawl over the ground surface but may have an erect habit in other situations.


Flowers are small and white. petals 2.5-3.5 mm long, greenish with pink or white margins. In contrast to other Polygonums, there is little or no honey or scent, so that the flowers are very rarely visited by insects and pollinate themselves by the incurving of the stamens. Flowering period May-October.



Leaves are alternate, oval, apex pointed and hairless 5-30mm long 1-8mm wide


Reproductive method

By Seed


Found mainly on arable land, however once established can be a problem in turf grass areas.

Miscellaneous info

Common Names: Knotgrass, Wireweed, Common knotgrass, Matgrass, Doorweed, Pinkweed, Birdgrass, Stonegrass and Prostrate knotweed.

The plant has astringent properties, and is used as a herbal remedy for treating diarrhoea, bleeding piles and all haemorrhages.

Cultural Control

Knotweed can be mechanically or physically removed. Care should be taken to assure that all roots are thoroughly removed. Close mowing reduces seed head formation and maintaining a dense sward will deter or prevent plantains from establishing. Regular aeration of the soil will help establish better grass growth and reduce the likelihood of compacted soils.

Chemical Control

Apply selective broadleaf herbicides when plant growth is active. There are a number of products available for controlling broad leaf weeds in established turf.

These chemicals are best used when the weeds are actively growing, usually between April-October.

  • Intrepid 2. (Contains 20.8g/L dicamba,166g/L dichlorprop-p ans 166.5g/L MCPA). Scotts.

  • Greenor. (Contains: 40g/L fluroxypyr, 20g/L clopyralid and 200g/L MCPA). Rigby Taylor.

  • Bastion T. (Contains: 72g/L fluroxypyr and 300g/L mecoprop-p ). Rigby Taylor.

  • Dormone (Contains 465g/L2,4-D(38.1%w/w) as the diethanolamine salt). A herbicide which can be used near water. Bayer Environmental Science.

  • Supertox 30 (Contains 95g/L (8.8%w/w) mecoprop-p and 93.5g/L(8.7%w/w) as the diethanolamine salts). Bayer Environmental Science.

These herbicides are usually applied as a liquid using watering cans, knapsack sprayers and vehicle mounted sprayers.

Ensure you follow manufacturer's directions, health & safety and product data sheets, and comply with COSHH regulations when using these chemicals.

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