Japanese knotweed is one of the most notorious and difficult invasive species to control. It spreads from rhizome fragments (which can be transported by water, animals, humans or as soil contamination) and can be very difficult to eradicate once it has taken hold. However, by following a few key guidelines, it is possible to prevent its spread and limit the scale of infestations.
Generally speaking, the best way to get rid of japanese knotweed is through a combination of approaches, and over time. A regular routine of cutting, foliar herbicide treatments and stem injections will eventually achieve eradication. The invasive plant management team at Acadia National Park, for example, uses a combination of these methods to manage established stands. Pulling or digging up the weed is usually ineffective and may actually stimulate new growth due to rhizome disturbance.
Cutting is important, especially during the growing japanese knotweed removal season, as it stops the weed from photosynthesizing. Regular inspection and clipping of any new shoots is also advisable. If you’re using a contractor to carry out work on your site, basic reputation and credential checks should help separate the wheat from the chaff, so always ask for references from previous clients and compare estimates before hiring anyone.
The Environment Agency recommends that you use a PCA-accredited firm that can offer an insurance backed guarantee with their work. This is a must for properties where knotweed is present as mortgage lenders will only lend on sites that have a risk assessment and treatment plan in place.
While some gardeners avoid the use of chemical weed killers, it is generally agreed that using high-quality glyphosate-based products is the most effective method for getting rid of knotweed. Glyphosate is a powerful herbicide which can be used to kill plants at all stages of development. When used correctly by a professional, it will kill the Japanese knotweed quickly and completely.
If you’re removing knotweed yourself, it is a good idea to use tarps to cover the area, and ensure that it doesn’t move. This will prevent it from spreading to other areas, and make it much more difficult for it to take root in the ground beneath it. If you have any doubts about using tarps, contact a reputable landscape expert for advice and guidance.
Lastly, never add any living Japanese knotweed to home compost or council-run garden waste bins as this is considered ‘controlled waste’ and you could be fined if you do so. It’s essential to dispose of it correctly at a licensed landfill site.
For a larger infestation, professional weed control specialists will have access to stronger chemicals than the general public and can often treat the problem in a matter of days. They will draw up a risk report and put in place a treatment plan that is guaranteed to remove the knotweed. This will be acceptable to mortgage lenders and property buyers, and will provide peace of mind that the site has been treated and is under control.