Reynoutria sachalinensis (giant knotweed or Sakhalin knotweed ) is a species of Fallopia native to northeastern Asia in northern Japan (Hokkaidō, Honshū) and the far east of Russia (Sakhalin and the southern Kurile Islands)
Reynoutria sachalinensis is a herbaceous perennial plant growing to 2–4 m (79–157 in) tall, with strong, extensively spreading rhizomes forming large clonal colonies. The leaves are some of the largest in the family, up to 15–40 cm (6–15.5 in) long and 10–28 cm (4–11 in) broad, nearly heart-shaped, with a somewhat wavy, crenate margin. The flowers are small, produced on short, dense panicles up to 10 cm (4 in) long in late summer or early autumn; it is gynodioecious, with male and female (male sterile) flowers on separate plants. The species is closely related to the Japanese knotweed, Reynoutria japonica, and can be distinguished from it by its larger size, and in its leaves having a heart-shaped (not straight) base and a crenate margin. Reynoutria sachalinensis has a chromosome count of 2n=44.
This plant is useful.
How to get rid of:
A comparative study of control measures used on the various knotweeds showed that digging led to a greater biomass reduction of F. sachalinensis than F. x bohemica, whereas cutting had the opposite effect. Mowing has been considered and a study in the Czech Republic using traditional meadow management with mowing and grazing suggested that such traditional management, provided it is applied continuously, may represent an effective barrier against invasion.
Japanese knotweed infested soil is dealt with as a contaminated waste issue in the UK, and as such its transport and burial are regulated by the Environment Agency.
A biological control programme has been underway since 2003 against the closely related Japanese knotweed, which has involved research on behalf of the UK, USA and Canada. In this time, surveys have been undertaken in Northern Honshu and Hokkaido where giant knotweed is the dominant or only knotweed in the area. Numerous natural enemies of giant knotweed have been identified including a northern strain of the sap-sucking psyllid Aphalara itadori, the chrysomelid beetle Gallerucida bifasciata and the pyralid moth Ostrinia ovalipennis amongst many other arthropods and fungi. Giant knotweed has not been the priority target so far but it is included in the host range testing procedures undertaken by the partner institutions so potential biological control agents may emerge in this on-going collaborative research project
It is rare to find specific information about the control of giant knotweed as separated from the more common Japanese knotweed for which there has been much written. In general the key to successful control with chemicals is to use a systemic chemical once the plant has reached its full height but before the first winter frost. In this way, the largest leaf to rhizome ration is presented and proportionally more chemical is absorbed through the leaves and moved along with the carbohydrates to kill the root. Herbicides containing glyphosate can be effective and have an advantage over the more persistent herbicides containing imazypyr, picloram and dicamba in that they have a lower soil activity. Care must be taken when using chemicals in general and especially on or near water where restrictions exist.