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A Brief Guide: ‘What is Japanese Knotweed (Fallopia japonica)?’


Japanese Knotweed Growing in a Garden

A Brief Guide: ‘What is Japanese Knotweed (Fallopia japonica)?’

Japanese Knotweed (Fallopia japonica) was introduced into the UK in the 19th Century as an attractive ornamental plant but it is now considered one of the most aggressive, destructive and resilient non-native, invasive species. Japanese Knotweed’s notoriously rapid growth allows the plant to colonise and completely dominate riparian ecosystems, destroying habitats of native herbaceous species and also solid structures. So much so, mortgage lenders may reconsider financing a loan if Japanese Knotweed is identified and not just within the boundaries of the property but also within the local area.

 ‘How is Japanese knotweed spread?’

Japanese knotweed is spread through fragments of the rhizome system or cut stems; it only takes a piece of rhizome the size of an AAA battery to produce a new plant. These knotweed fragments can be spread very easily and innocently in the tread of a tyre, on the sole of a shoe or attached to a piece of clothing. The destructive nature and rapid growth of Japanese knotweed means that it must be identified, controlled, eradicated and treated as quickly and safely as possible.

Although it is dormant for winter at present, Japanese knotweed will start to grow again in the spring, with shoots appearing in late March to early April. This is when knotweed identification is vitally important. Japanese knotweed shoots are similar to asparagus spears but have a purple tint to their colour and within a couple of months these shoots will rapidly grow into large mature plants.

‘What does Japanese knotweed look like?’

 Identifying Japanese knotweed is relatively easy once you know what you are looking for (or check out our gallery) as the plant is really quite distinctive and very large once mature. Japanese knotweed has large, shield-shaped leaves that grow in a zig-zag from the reddish coloured stem (sometimes green speckled with red), then towards the autumn knotweed produces creamy-white flowers.

If any company or person suspects they have Japanese knotweed on their land then they must contact a reputable and qualified weed control company, such as Invasive Weeds Agency, before removing any plant material from site in order to ensure that the procedure is in line with the law.  Japanese knotweed eradication requires fully trained Japanese knotweed control experts to manage the project as knotweed can spread very easily if handled or disposed of incorrectly.

‘How do I get rid of Japanese knotweed?’

Quite simply, you don’t. Leave it to the experts. Although difficult to eradicate, it is possible to treat Japanese knotweed using an annual application programme of herbicide but this may be considered damaging to the environment. However, it is the most common method of knotweed eradication as it is cost effective and suitable for most situations. The herbicide is usually applied over the summer months but this can take years to fully control and eradicate the knotweed. The knotweed stand can also be excavated and buried 5m below ground within a root barrier membrane, this is a very quick way to control knotweed rhizome but this should be done by a qualified Japanese knotweed control company because incorrect disposal can lead to further spread of this weed and damage to the environment. Any fragments of the plant that are not within the membrane can produce new shoots and eventually a new knotweed stand, therefore deeming any prior work pointless. This is why Japanese knotweed control must not be tackled by anyone and the responsible party must be by a licenced and competent knotweed control company.

It is against the law for any person to knowingly allow the spread of Japanese knotweed into the wild; therefore, should the removal of Japanese knotweed be carried out incorrectly and the weed is spread then the offending person or company may be charged due to contravention of the Wildlife and Countryside Act 1981.

For further advice on Japanese knotweed eradication, call Invasive Weeds Agency now on 0845 676 9252 or contact us here.

IWA. Getting to the root of the problem.