JAPANESE KNOTWEED
Introduced to Britain in the 19th century as an ornamental plant, Japanese knotweed is a tall, vigorous perennial that can quickly grow to over 3m in height, with a complex underground network of rhizomes which may extend to a depth of 3m and 7m laterally from visible, above-ground plants.
The aggressive growth pattern of Japanese knotweed is capable of exploiting weaknesses in hard engineered structures such as concrete, tarmac and brick. Early intervention can limit this damage, prevent spreading and stop any civil actions (as it is an offence under the Wildlife and Countryside Act 1981 to cause it to grow in the wild, or plant it in the wild).
Japanese knotweed's rhizomes can remain viable for several years without producing visible shoots above ground, but when disturbed, regrowth may appear. Several control methods can be implemented, however, disturbing the plant and rhizomes can also lead to further spread.
Japanese Knotweed Through the Seasons
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Red shoots
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Red stems, lighter shade green tips (similar to asparagus)
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Greenish shoots
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Green stems speckled with purple/red; alternate leaves (left then right)
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Bamboo like hollow stems, green alternate leaves, small white flowers
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Brown outer skin on stem (can peel); remains of flowers
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Smooth, light-coloured, brittle canes
Types of Japanese Knotweed Treatment
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In-situ herbicide treatment: This is the application of herbicide to the foliage.
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Combined excavation to landfill and herbicide treatment: This method removes the majority of the stand(s) to landfill, leaving any sensitive areas in-tact. These areas are then treated with herbicide.
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On-site treatment, ex-situ: Japanese knotweed contaminated soil is excavated and moved to a more convenient area of the side for stockpiling and ongoing herbicide treatment.
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On-site burial: Contaminated soil is buried in a 5m-deep cell lined and encapsulated with a root barrier membrane. This is then capped with clean topsoil.
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Off-site disposal: This option can be used as a last resort when other options are not viable.
ERS has extensive experience in identification, management and remediation of Japanese knotweed infested sites. We work with clients to develop a treatment strategy which meets their timescales, budget and future development requirements.
When Japanese knotweed is identified on site, ERS can develop and implement a Japanese knotweed management plan. This plan is essential, both for the current owner and any future owners, as a record for treatment of the site
ERS are members of the Property Care Association (PCA) and are able to provide up to a 10 year insurance backed guarantee for the treatment of Japanese knotweed.
To enquire about a survey or management plan for Japanese knotweed on your site, contact us today to speak to one of our Invasive Weeds experts.