Japanese Knotweed and another species Giant Knotweed, Fallopia sachalinensis, and Hybrid Knotweed, Fallopia japonica x Fallopia sachalinensis are Schedule 9 species on The Wildlife and Countryside Act 1981 (Variation of Schedule 9) (England and Wales) Order 2010. Under this act it is an offence to plant or cause to grow any plants listed in Schedule 9.
The stems grow vigorously from mid to late May dominating areas and creating stands where it is the only species present. The dried stems from previous years are generally present. Fresh stems are green and red with a similar appearance to rhubarb and can grow in excess of two metres in height. The leaves have a stem, are oppositely arranged on the stem. Stems are hollow. Later in the season small creamy white flowers appear in the leaf axils.
Rhizomes (underground stems that are capable of producing the stems and roots of another plant) grow rapidly underground producing long white shoots at the tips which send up shoots to the surface. Disturbance increases the stem density and if the tops are cut it is important to dispose of them properly.
All Japanese Knotweed plants within the UK are female and all male plants are shown to be infertile hybrids. Japanese Knotweed has an incredible capacity to spread: as little as a 10mm2, 0.7 gm section of rhizome has the capacity to produce a whole new plant. The plant spreads vegetatively from stems, crown and rhizomes and has spread throughout the entire UK since its arrival here in 1854.
Cultural – Japanese Knotweed can be excavated and then either removed from site which requires a specialist/properly licensed organisation to remove the waste from site where it must then be transported to a licensed waste facility. (The Environmental Protection Act 1990 contains a number of legal provisions that designate Japanese Knotweed contaminated soil as ‘controlled’ waste.) Or Japanese Knotweed can be excavated and then buried on-site, but unless it can be covered with 5 metres or more of overburden, a specialist root barrier membrane should be installed to fully or partially encapsulate the Japanese Knotweed-bound soil, to prevent any regrowth.
Chemical – Chemical control is often the most cost-effective means of controlling Japanese Knotweed and refers to applying a professional herbicide over a period up to three years depending upon the infestation. The main consideration is the locality of the plant in relation to water. Consent is needed from the Environmental Agency if herbicides are to be sprayed near water. In situations near water it is advisable to use a method of application known as ‘Stem Injection’. This method of application is labour intensive but minimises the herbicide coming into contact with other plants and is particularly effective later in the year when the plant is marshalling resources into its extensive rhizomes for the next year’s growth.
The ALS Contracts Team can be contacted on 01952 898518/9 for enquiries regarding Japanese Knotweed Control or email firstname.lastname@example.org