Kingcombe Aquacare Specialists in Water Management, Water Engineering and Maintenance for Landscapes, Fisheries, Leisure and Conservation

Specialists in Water Management for Landscapes, Fisheries, Leisure and Conservation

Alien Invasive Weeds

Warning as killer weeds endanger our plant and water life

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, Brussels has banned the only known weed killer that can eradicate some of the worst offenders.

Giant Hogweed

Banning of the chemical Diquat alginate will allow the spread of invasive weeds to such an extent that 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.

"We all have to act extremely quickly to get rid of these atrocities before existing stocks of Diquat alginate are exhausted.," according to John Colton, managing director, 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. It's just typical of EC bureaucrats to ban the only effective weapon we had in our fight to eradicate these foreign invaders from our island. 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!

Australian Swamp Stonecrop, Water Fern and Duckweed

Spring growth of Japanese Knotweed
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.

Unfortunately, due to EEC legislation, effective herbicides will soon be unavailable for tackling this plant, so it is important to deal with the problem now, while we still have the means to do so,

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 it by mechanical means just does not work with this weed and will certainly 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.

Parrots Feather

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.

Pennywort encroaching onto grassland

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.

Back to Maintenance