Japanese knotweed (JK) is an invasive plant species in the UK (after being introduced in the 19th century as an ornamental plant). It spreads widely and reduces native biodiversity, it is difficult to control and can grow in cracks in buildings, walls and paths leading to lasting damage. Mortgage lenders in the UK may require property buyers to put management plans into place if JK is found on their or a neighbouring property which can add a significant cost. Many JK control companies offer to eradicate the plant in a short period of time, but complete below surface removal of the plant is very difficult and can take many years.
Dan Eastwood and Dan Jones undertook the world’s largest JK control field trial starting in 2012 working with company sponsor Complete Weed Control Ltd. Over 5 years they tested 19 of the main physical, chemical and integrated methods of controlling JK. Based on these field trials they developed a 4-stage method, which uses glyphosate herbicide at specific times of the year. This seasonal targeting with specific herbicides linked to the plant’s biology delivers better results with lower doses of herbicides which is better for the environment and cheaper for the landowner.
The field trials are still ongoing and new products and approaches to control the plant are being tested along with a new long-term study to regenerate previously invaded land using native plant seed mixes to suppress further non-native plant invasions.
The new 4 step model has been adopted by commercial JK control companies, National Rail (in Wales) and public land managers (such as county councils). Working with Michael Draper in Swansea University’s Law Department, the team help change the Law Society of England and Wales conveyancing documentation in 2020 in response to this research, recognising that knotweed control plans do not eradicate the plant. The latter affects ca. 1,000,000 conveyancing events per year in England and Wales.