Japanese Knotweed (Polygonum cuspidatum)

 

Japanese knotweed (Polygonum cuspidatum) is a large, herbaceous perennial plant, native to eastern Asia in Japan, China and Korea. In the UK the species is has been classified as invasive. It is illegal to promote its growth by the Wildlife and Countryside Act 1981.

A member of the family Polygonaceae, Japanese knotweed has hollow stems with distinct raised nodes that give it the appearance of bamboo, though it is not closely related. they are Green, with red or purple specks and form dense cane-like clumps.

While stems may reach a maximum height of 3–4 m each growing season, it is typical to see much smaller plants in places where they sprout through cracks in the pavement and are cut down on a regular basis. The leaves are broad oval approximately, 7–14 cm long and 5–12 cm broad. green, shield or heart-shaped, with a flat base, the flowers are small, creamy white on stems about 6–15 cm long in late August through to mid September.

Japanese knotweed was first introduced to the UK in the late 19th century for its attractive covering foliage and flowers by the Victorians. Little did they know it would cause such problems.

An interesting fact about Japanese knotweed is that it is a concentrated source of emodin used in stomach upsets. The roots are used in traditional Chinese and Japanese herbal medicines as a natural laxative.

Japanese knotweed is notoriously hard to kill due to the fact that it spreads via rhizomes rather than seed.

 

Since 1980 we have been controlling Japanese knotweed with success. We now come to the final eradication.

The method we have found to be the easiest and cheapest is to use a spraying technique using GLYPHOSATE. You use this when it is in flower which is late August early September. The best time to spray is early morning or evening when no rain is forecast for at least 6 hours after spraying.

Once you leave the product to do its job it will take anything up to 4 - 6 weeks. After this time you will have noticed the change to give a strong dark brown coloration and a noticeable dead appearance.

The images below show the Japanese knotweed in various stages of the treatment. The test we have done is to prove the effectiveness of this method and to control the spread to other areas of the Chine. Next year we plan to expand our programme.

 

We hope you find this information helpful.