Japanese Knotweed Survey
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Japanese Knotweed Survey

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Japanese knotweed foliage

Japanese knotweed foliage

Japanese knotweed stems

Japanese knotweed stems

 

Japanese Knotweed Identification  

tel: 0333 456 7070
mob: 07950 259 905

Introduction

Many knotweed species, particularly Japanese knotweed, Giant knotweed and Himalayan knotweed are considered noxious, invasive weeds. Like many such weeds, Japanese knotweed was introduced from Japan into the U.K., in the 19th century as an ornamental plant. In its native countries of Japan, North China, Korea and Taiwan, the weed presents nowhere near the problem it now poses across the UK. With its natural habitat being on the slopes of volcanoes, it is no surprise that the less harsh and more fertile environment of Britain has allowed this plant to flourish to extreme proportions.

Japanese knotweed is a perennial (winter hardy herbaceous plant) and extremely invasive. It thrives on disturbance. The tiniest piece can re-grow. Root and stem fragments as small as 0.7grams (dry weight) can form new plant colonies. Japanese knotweed has been spread by both natural means and by human activity. It soon overruns riverbanks, railway embankments and road verges. In coastal and riparian areas, high water flows disperse fragments of the plant downstream where new colonies form. In the past, fly-tipping and transportation of soil containing rhizome fragments have been a major cause of establishment, particularly in the urban environment. Green waste recycling schemes are also sites of potential contamination which is a cause for concern.

Some knotweeds grow extremely quickly during the spring; Giant knotweed can reach 4.5 m by summer, Japanese knotweed 3 m, and "dwarf" Himalayan knotweed 1.5–2 m. Some species can spread rapidly from an extensive network of rhizomes (roots that can sprout) spreading from 7–20 m from the parent plant and at least 3 m deep. Floods and high water events wash whole or partial plants into rivers and creeks, dispersing pieces of Japanese knotweed throughout the flooded area and banks, which give rise to new plants. As with other invasive species of plants, freshly disturbed soil allows the rapidly growing young knotweed plants to outgrow other plants and take over the area, suppressing other species. Cutting, mowing, digging and some herbicide treatments, especially in early to mid growing season, fail to curb knotweed growth and in fact often stimulate the production of shoots from latent buds dispersed on the root crown or rhizomes.

Identification

In the early spring red/purple shoots appear from the ground and grow rapidly forming canes. As the canes grow the leaves gradually unfurl and turn green.
In spring, the newly expanded leaves are a yellowish green, becoming darker as they mature through summer. They alternate along the stem forming a zigzag pattern.The plants are fully grown by early summer and mature canes are hollow with a distinctive purple speckle and form dense stands up to 3 metres high. The plant flowers in late summer and these consist of clusters of spiky stems covered in tiny creamy-white flowers. The seeds are rarely fertile and in Britain the plant spreads mainly by vegetative means.

The canes arise from the rhizome which grows underground, from an existing crown, where previous growth has taken place, or from a cut stem. Towards the end of autumn, leaves begin to turn a yellowy-brown and eventually drop, revealing feathered branches from the remains of the flowers. Hollow canes shed the darker outer skin exposing a lighter, smooth cane that is quite brittle. The canes remain standing throughout the winter and can often still be seen in new stands in the following spring and summer.

The rhizome is the underground part of the plant. It is knotty with a leathery dark brown bark and when fresh snaps like a carrot. Under the bark it is orange or yellow. Inside the rhizome is a dark orange/brown central core or sometimes it is hollow with an orange, yellow or creamy outer ring, although this is variable. Young rhizomes are very soft and white. The 'knots' are nodes, spaced at 1-2cm intervals where there are often small white fibrous roots or buds emerging. Each of these 'knots' can potentially become a new plant if the rhizome is cut up (e.g. through digging).

> Identification Service

Not sure if it is Japanese knotweed? Email photographs for our surveyor's expert opinion.

We can also send a surveyor's letter identifying the plant in the photographs if required.
*fees and conditions apply

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Company’s Registered Office Address: 597 Etruria Rd, Basford, Stoke On Trent, Staffordshire. ST4 6HP.
Japanese Knotweed Survey © Copyright 2011

Japanese knotweed survey, management, control, eradication & land remediation relief.
Areas include Staffordshire, Cheshire, West Midlands, Manchester, Birmingham & Stoke On Trent.

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