|Fallopia japonica subsp. var.||Japanese knotweed|
Japanese Knotweed (Fallopia japonica, syn. Polygonum cuspidatum, Reynoutria japonica) is a large, herbaceous perennial plant, native to eastern Asia in Japan, China and Korea. In North America and Europe the species is very successful and has been classified as invasive in several countries.
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. 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 or are repeatedly cut down. The leaves are broad oval with a truncated base, 7–14 cm long and 5–12 cm broad, with an entire margin. The flowers are small, cream or white, produced in erect racemes 6–15 cm long in late summer and early autumn.
Closely related species include giant knotweed (Fallopia sachalinensis, syn. Polygonum sachalinense) and Russian vine (Fallopia baldschuanica, syn. Polygonum aubertii, Polygonum baldschuanicum).
Other English names for Japanese knotweed include fleeceflower, Himalayan fleece vine, monkeyweed, Hancock's curse, elephant ears, pea shooters, donkey rhubarb (although it is not a rhubarb), sally rhubarb, Japanese bamboo, American bamboo, and Mexican bamboo (though it is not a bamboo). There are also regional names, and it is sometimes confused with sorrel.
The invasive root system and strong growth can damage foundations, buildings, flood defences, roads, paving, retaining walls and architectural sites. It can also reduce the capacity of channels in flood defences to carry water.
The most effective spraying solution contains about 5%-10% glyphosate in water. (To make a 5% solution from a 40% concentrate mix 1 part concentrate with 7 parts water.) Ready-to-use solutions that contain less than 5% glyphosate are too weak and do not work. A small amount of liquid dish-washing detergent can be added to improve wetting of the leaves. If possible, both sides of the leaves should be sprayed until they are completely wet. It takes about 3 weeks for most of the plants to die. After 3 weeks, all remaining plants should be sprayed again. This process needs to be repeated until all the plants die. The US federal government will come and spray Japanese knotweed for no charge in many areas under the Invasive Species Act. Local county extension agencies can be contacted for more details.
Pests and diseases
- ↑ Biological control of invasive plants in the Eastern United States
- ↑ IUCN Global Invasive Species Database
- ↑ Article on the costs of Japanese Knotweed