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Japanese Knotweed Catchment Map

Non-native plants from around the world have historically been brought to Scotland for botanical garden collections and accidentally imported with other goods. Most do not cope well with the Scottish climate but a few become invasive and have a negative ecological and economical impact. The three main species are Japanese knotweed, Himalayan balsam and giant hogweed. The catchment has been surveyed and mapped and an eradication programme began in 2010. To find out more click on the plant name ad follow the link.

To prevent the spread of INNS good biosecurity is essential and the River Annan Trust Bioscurity Plan is available for download or you can visit our biosecurity page here.

Japanese knotweed
(Fallopia japonica)

Japanese knotweed is a hardy perennial plant introduced to Britain in the 19th century for garden collections. The sharing of plant cuttings and the discarding of unwanted rhizomes meant it didn’t take long for it to spread into the wild, particularly on waste ground and along water courses. Knotweed grows rapidly and quickly displaces native plant species while providing poor habitat for mammals, birds and insects. Moreover, it causes huge economic problems, particularly for the construction industry as it has the ability to grow through concrete and asphalt. It is estimated to cost the Scottish economy £4.4 million per annum.

The primary method of controlling Japanese knotweed is the stem injection system. Although a little more time consuming it has proved to be effective whilst having no impact on surrounding vegetation. Unlike the knapsack sprayer it doesn’t require a period of dry weather to be effective, which has meant control can continue through the wetter summers we have experienced recently.
Since the initial mapping in 2008 the volume of knotweed has grown as new stands have been found and knotweed stands have increased in size. A more recent survey approximates that there was 9500 M2 of knotweed within the Annan catchment at the start of the project.

Since the start of the project 112 stands of knotweed have been treated, totalling 5313 M2 over 16 miles of river bank. This leaves just 28 stands in the main catchment area, although one of these stands is 3000 M2.
The control of Japanese knotweed appears to have been very successful. Treated stands have shown a reduction of at least 95% is most cases. It is important that we continue to monitor these areas to ensure we keep on top of any re-growth.
Some assistance with the knotweed project has been provided by the Apex Trust, an organisation that provides opportunities for people with criminal records to learn skills for employment. The project provided funding for 2 Apex volunteers to gain a qualification in the safe use of pesticides.

Other Resources​

Report Japanese Knotweed:

Download the Japanese knotweed ID sheet here


View the GB Non-Native Species Secretariat fact file


Cabi biological control project

Japanese Knotweed River Annan
Japanese Knotweed River Annan

Japanese knotweed distribution within the Annan catchment

Giant Hogweed

(Heracleum mategazzianum)

​Giant hogweed is another plant introduced for garden collections in the late 19th century and can easily be distinguished from the native common hogweed (Heracleum sphondylium) by its huge size.  Giant hogweed can grow up to 5 metres tall while common hogweed will never be more than 2 metres.  It spreads solely by seed and can produce up to 50,000 of them which can be viable for 10 years or more. Similarly to other invasive plants, giant hogweed outcompetes and suppresses native species but it is also a health hazard. Giant hogweed is a phototoxic plant and the sap can cause painful blisters on the skin when exposed to sunlight.  These blisters can cause scars which persist for many years.
We are lucky on the River Annan that we have very few of these plants and they are confined to one area which was discovered in 2012. They have been treated using the stem injection system and this appears to have been effective. We will need to monitor the treated area for some time as the seeds can remain viable for many years.

Other Resources

Report Giant hogwed:

Download the giant hogweed ID sheet here

View the GB Non-Native Species Secretariat fact file

Giant Hogweed
Giant Hogweed

Invasive Non-Native Species Project

Report an Invasive Species


Tel: 01576 470600



Contact Us


Fisheries Office
Annandale Estates, St Ann's
Tel: 01576 470600

Mobile: 07710331079

American Skunk Cabbage
(Lysichiton americanus)

American skunk cabbage is native to western North America, from northern California to southern Alaska. It was introduced into the UK in 1901 and was first reported as an escapee in 1947 in Surrey. Skunk cabbage has been widely planted in gardens around ponds and up until recently was readily available to buy, even receiving the Royal Horticultural Award of Garden Merit. Skunk cabbage prefers wetland/boggy areas rather than river banks, however over 60 plants have now been removed from the River Annan. It does produce seeds which allow it to spread over short distances. In its native range squirrels and birds can help to disperse the seeds further from the parent plant.

Over the last few years we have removed 60 skunk cabbage plants from the banks of the River Annan, anecdotally it seemed to be on the increase (although we don’t have any pre-removal data to back this up) and we decided to take action before it became a problem. The plant can be dug out, although for larger, well established plants this can be a difficult task.    

Other Resources

Report Skunk Cabbage :

Download the skunk cabbage ID sheet here

View the GB Non-Native Species Secretariat fact file

Giant Hogweed
Giant Hogweed
Photo: NNSS

Himalayan Balsam

(Impatiens glandulifera)

Another plant brought to Britain for garden collections in the 19th century is the highly invasive Himalayan balsam. Balsam often forms dense monocultures reducing the diversity of plant life, particularly in the riparian strip were it thrives. The die back of large areas of balsam in winter can leave river banks bare making them vulnerable to erosion and flooding. Although the plant can be popular with be keepers as it produces large amounts of pollen, this also impacts on native plant species as balsam is pollinated rather than native plants, reducing their seed production.
As it is an annual plant, the aim of control work is to remove it before it can set seed and eventually exhaust the seed bank. Himalayan balsam control has been carried out in partnership with the Criminal Justice Service who have provided an unpaid workforce of around five people to cut and pull balsam from the river bank. This element of the project finished in 2011 and in 2012 we began working with the Apex Trust. In conjunction with this a number of volunteer days have been organised to help remove this plant from the river bank.
As part of the project the CJS unpaid workers received training in the safe use and maintenance of a brushcutter. While enabling the recipients of these qualifications to contribute significantly to the removal of balsam it also provided them with demonstrable skills they can use in the future. Approximately 2 kilometres of river bank have been worked on to date.

Other Resources

Report Himalayan balsam:

Download the Himalayan ID sheet here

View the GB Non-Native Species Secretariat fact file

Cabi biological control project

Himalayan Balsam Catchment Map

Himalayan balsam distribution within the Annan catchment

Balsam Bash
Balsam Bash
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