Japanese knotweed (Fallopia japonica)
Japanese knotweed does not produce seeds and spreads from cuttings of rhizome and plant stem. A finger nail piece of plant material is all that is needed for a new plant to grow. Because of this it is essential that Japanese knotweed is controlled correctly.
- Never throw away or fly tip plant material or soil – under the Wildlife and Countryside Act 1981, it is an offence “to plant or otherwise encourage in the wild” the growth of Japanese knotweed
- Avoid strimming, flailing, mowing or chipping Japanese knotweed – pieces of stem as small as a fingernail can grow into new plants
- Scottish Environment Protection Agency (SEPA) must be contacted before using chemicals in or near water.
- Removal of plant material off site must be undertaken by a licenced carrier.
- Report Japanese knotweed to firstname.lastname@example.org
Key ID Features
Purple speckled stems
Regular nodes (like bamboo)
Creamy clusters of flowers (Aug to Oct)
Ability to grow through weaknesses in concrete and asphalt
Large shield shaped leaves - can grow up to 120mm long
Flat at base of leaf
- Spraying with a commercial glyphosate-based chemical is effective on Japanese knotweed. Spraying needs to take place at least twice during the growing season, once the plant is fully in leaf but before flowering. Over a period of 5 to 7 years the plant will be controlled although eradication is unlikely. The area needs to be checked annually to treat small areas that may have re-sprouted.
- Injecting the plant with a stem injection unit is very effective and can reduce the plant in size by as much as 95% in one year. This works by injecting a measured dose of herbicide into each cane of the Japanese knotweed infestation which allows the herbicide to translocate throughout the roots and rhizome of the plant.
- Grazing will suppress growth but cannot completely eradicate the plant.
Best Methods of Control
Do's & Don'ts