Japanese knotweed (Fallopia japonica) is an increasing problem within the county. The invasive alien plant, which was introduced into the UK as an ornamental plant in the 1800s, is most often found in urban settings and along water courses but increasingly turns up all over the county in rural hedgerows and building plots. It was first noticed in the wild in 1900 and by the early 1960s colonies stretched from Land’s End to the northern tip of the Isle of Lewis. Just a tiny piece of the plant’s rhizome (root) can be enough to allow the plant to spread. These pieces can easily be carried on a vehicle’s wheels. Allowing this spread or intentionally introducing Japanese Knotweed into the wild is illegal under the Wildlife and Countryside Act 1981. Without the plant’s proper eradication from a site it can be problematic for many years –reappearing even through concrete and tarmac. Eradication usually involves the use of strong herbicides over aperiod of years. This can obviously have adverse effects on adjacent vegetation and some persist for some time in the natural environment and enter water courses.

Research carried out by CABI (Commonwealth Agricultural Bureaux International) and funded by a number of organisations, including WAG and the Environment Agency have been undertaking research to look at potential natural control of Japanese Knotweed.

UK and Japanese organisations have worked together on the project. In Japan the plant does not cause the problems it does in this country. There it has natural herbivores and diseases that attack it and keep it in check.

Plants there can be heavily defoliated and suffer stem damage.

In the UK all the plants are thought to be clones of a single original plant. The plant cannot form seeds but spreads through root growth or movement of the rhizome. Imagine how the plant could spread if it had viable seeds!

Because the plant is a clone scientists could establish that theplant originated from Omuraarea on Kyushu Island. Survey expeditions to Japan were carried out and samples ofinsects and fungi found on knotweed growing there were collected. Around 50 species of fungi and 186 species of arthropod (insects, spiders, etc.) were found to be associated with Japanese Knotweed. The researchers, after studying and dismissing a number of candidates, narrowed the list down and are focusing on a sap-sucking insect and a leaf-spot fungus. Studies on both of these looks promising and research is continuing this year. Care must be taken as Japanese Knotweed is in Polygonaceaefamily, which also includes native British species such as the bistorts and knotgrass. Introducing a pathogen that starts attacking our native species could have devastating outcomes.

In Japan the young shoots of the plant are used as a vegetable, and Richard Maby’s Flora Britannica states that ‘in parts of Dyfed the young shoots and leaves are cooked like spinach’. Maybe this needs to be further investigated!