Foreign, water-borne weeds are already beginning to clog our rivers, lakes and ponds. As this invasion of pernicious and environmentally deadly flora reaches epidemic proportions, the balance of nature of our countryside and parks will come under threat, endangering the very existence of many species of our own indigenous plant and water life.
John Colton, managing director of Kingcombe Aquacare, says: “These weeds are extremely hardy and their presence in our inland waters is now an extremely serious issue. They are not only destroying our environment, but are now beginning to have a negative effect on our water margins, fish and pond life. I would ask anyone finding a colony of these weeds on their land to get them eradicated as best they can and as soon as they can.”
The first hurdle is to recognise an incursion of these weeds when you see one. To help in their identification, the photographs on this page are accurate recordings of examples of the main offenders. Should you have an outbreak you can’t control, contact us for advice.
Sharing first place on the list of non-native, pernicious weeds are the Australian Swamp Stonecrop (Crassula helmsii) and the Japanese Knotweed (Fallopia japonica), followed closely by Giant Hogweed (Heracleum mantegazzianum) and Floating Pennywort (Hydrocotyle ranunculoides).
Unfortunately, getting rid of them is not easy as each species has to be eradicated using different techniques. What will work for one can actually accelerate the continued spread of another!
As an example, the Australian Swamp Stonecrop, which was introduced from Tasmania as an “oxygenating plant” in 1927, must be controlled by chemical rather than mechanical means. Any fragments resulting from cutting or tearing can re-grow and worse, spread the infestation downstream. Fragments as small as one node (5mm) can re-grow. Special herbicides are the only answer.
Japanese Knotweed is rapidly colonising river banks and areas of waste land forming dense stands up to 3 metres high in summer, severely impeding access to river banks and shading out native species, leaving banks bare and liable to erosion in winter. Then, it survives in the form of rhizomes which grow rapidly and have been known to grow through rock, tarmac and concrete, damaging embankments and structures.
Killing by mechanical means just does not work with this weed; in fact, such efforts assist its spread as even the smallest surviving fragments have the ability to re-grow. Spraying with the chemical Glyphosate will work, but further applications will almost certainly be necessary.
Another alien weed to watch out for is the Giant Hogweed. Its sap contains a toxic chemical which sensitises the skin and can lead to blistering of the skin when exposed to sunlight. Once a plant has produced seeds, it can be assumed they will be present in the surrounding area – and it is believed they can remain viable for up to 15 years. A chemical treatment is available, but the timing of application is critical if it is going to be effective.
Floating Pennywort was introduced into the UK from North America as a plant for tropical aquaria. It roots in the margins of slow-moving waters and lakes and forms dense mats of vegetation. It has been recorded as growing up to 20cm per day! This weed has proved particularly difficult to control and can cover the surface of waters interfering with the ecology and amenity value of any water it may infest.
Cutting Floating Pennywort is only a short-term solution as it can grow back to its former bulk extremely rapidly. There is a chemical solution, but the timing of its application is critical to any success. However, any application of herbicides to water can only take place with prior approval from the Environment Agency. Kingcombe Aquacare arranges all the necessary consent on behalf of their clients. The best solution is to remove any stands of this weed as soon as they are spotted and before it has had a chance to fully establish itself.
If you think you have an invasive weed problem and you would like some advice, phone and speak to our Environmental Manager on 01460 279 200.
The list below names current species of GB non-native aquatic plants. To view a data sheet for each plant please click on the relevant name. All data sheets are linked to – with thanks – from the GB non-native species secretariat website.
- Australian Swamp Stonecrop/New Zealand Pygmyweed (Crassula helmsii) (around 4.5MB)
- Canadian Pondweed (Elodea canadensis) (around 500KB)
- Curled Pondweed (Lagarosiphon major) (around 900KB)
- Floating Pennywort (Hydracotyle ranunculoides) (around 2.7MB)
- Giant Hogweed (Heracleum mantegazzianum) (around 7.3MB)
- Himalayan Balsam (Impatiens glandulifera) (around 5.2MB)
- Japanese knotweed (Fallopia japonica) (around 4.7MB)
- Parrots Feather (Myriophyllum aquaticum) (~ 3.3MB)
- Water Fern (Azolla filiculoides) (around 2.9MB)
- Water Primrose (Ludwigia peploides) (around 2.8MB)
If you think you have an invasive weed problem and you would like some advice, please phone and speak to our Environmental Manager on 01460 279 200.