ABSTRACT
Japanese knotweed is the plant that every one loves to hate; it is regularly the subject of newspaper articles, where it attracts epithets such as monster, triffid barbarian and so on. The general public are terrified that it is going to turn up in their gardens and developers worry about potential costs of infestations on their sites. Environmentalists despair as continuous stands cover mile after mile of picturesque and ecologically sensitive rivers, while politicians look aghast at the vast sums spent on herbicides and removal of this plant. Japanese knotweed is indeed a very successful plant in Europe and is particularly at home in the more western regions. In its native Japan it is just one component of a giant herb community, where it must compete with other giant herbs such as Miscanthus. It is rarely considered to be a problem in Japan, where it is preyed upon by a large range of invertebrates, and struggles to find a niche along riverbanks and forest edges. Each year it grows to about 3m in height and by autumn is covered with small white nectiferous flowers; it is then cut back to the ground by the first frost, and overwinters with its extensive system of woody rhizomes. What might appear to be profligate vigour in the plant’s growth in Europe is the bare minimum needed to compete successfully in its native regions. Much has been written on theories of invasion and invasability; but the consequences of transferring a heavily predated plant from an intensively competitive giant herb community to an environment where it towers over the native herbs and is ignored by the native invertebrates are scarcely surprising! Due to its rhizome (small fragments of which can produce a new plant), the plant is spread vegetatively along watercourses and by people’s earth-moving activities. On account of the rhizome, well-established stands are extremely difficult to eradicate by herbicide alone.
