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Invasive Species


Invasive Non-Native Species can have huge impacts on humans, wildlife and the environment. These organisms are non-native to the area in which they are found, and as such don't have predators or diseases adapted for them in the environment. This allows them to move into new areas without being afflicted by the problems native species have, and outcompete them. This can not only result in a huge decline in native biodiversity, but can also have substantial physical impacts on the environment.

The two predominant Invasive Species living on the River Clun are Japanese Knotweed and Himalayan Balsam. Both of these plants grow in the summer and die back in the winter leaving bare ground. With winter weather this can lead to riverbank erosion and mud entering the river and clogging the gravel at the bottom which can have serious negative impacts on local wildlife (e.g. the suffocation of fish eggs, reduction in habitat for fish spawning and freshwater insects, less food for birds and otters).


Japanese Knotweed

Japanese Knotweed.JPG

Japanese Knotweed is a plant that was introduced from Eastern Asia (Korea, China & Japan). The plants originally arrived in the UK in 1850 when it was sent to Kew Gardens, in London, shortly after that it arrived to the Royal Botanic Gardens in 1854. Following this the plant was sold to gardeners the country over and from there it has gradually been taking over the countryside.

Japanese Knotweed is particularly infamous due to it's ability to grow through concrete and damage buildings, paths and walls. When it comes to selling a house with Knotweed on the grounds you may find that buyers find it difficult to get a mortgage unless a set multi-year treatment plan is in place. 

One of the reasons the plant has beccome so prolific is that a broken stem or fallen leaf when lying on the ground can grow into a whole new plant. Under no circumstances is cutting or strimming JK recommended as this only serves to spread the plant. This method also raises the problem of dealing with the cut material which becomes controlled waste and must be sent to a licensed landfill facility willing to accept this waste. Leaving the cut material to decompose in situ is not acceptable as it can re-grow thereby increasing the problem.​

There are two effective methods of getting rid of Japanese Knotweed, spraying or stem injection of the plant using Glyphosphate based herbicides (e.g. Roundup Pro Biactive).  The timing of treatment is important with the most effective results occuring when the plant is in flower (around autumn) as the herbicide is absorbed more readily into the roots of the plant. Re-growth in spring should be treated with the same methods. Ongoing monitoring of the stands is essential due to the persistantness of the plants, it is very likely that more than one application of glyphosphate will be nessesary to kill the plant.

Himalayan Balsam


Balsam flowers and seeds.jpg

​Also known as Policeman's Helmet these pretty flowers were also introduced by the Victorian's into the country as ornamental garden plants. The seed pods produced by these plants have explosive tendancies when ripe which can send the seeds scattering up to 7m away from the original plant.

Bee's love the nectar from these plants but it comes at the cost of native plants, which suffer by not getting pollinated, and the subsequent outcompeting of the Balsam ultimitely leading to the loss of native plants from the area.

The most effective method of removing Himalayan Balsam is to pull it. When in In spring and summer Himalayan Balsam can easily be pulled by the roots from the ground. If left to hang on a tree, or tarpaulin the plant will dry out and die. Do not try pulling Himalayan Balsam after it has gone to seed (see second picture) as the seed pods will probably explode, spreading the plant further throughout the site.

Cutting the plant is also an option, however to destroy the plant it MUST be cut below the lowest node or it will regrow and flower later in the season.​ Again this must be done before the plant has gone to seed.

Further Information: 


"Japanese knotweed, giant hogweed and other invasive plants"​, UK Government (2013) -

https://www.gov.uk/japanese-knotweed-giant-hogweed-and-other-invasive-plants