Japanese knotweed is an invasive species that can cause a lot of damage to both property and the environment. There are a few methods people use to control it, but none are 100% effective.
The most common way to control Japanese knotweed is through herbicides, though this can be expensive and time-consuming, especially if you have a large area to cover.
Another option is physical removal, which is often the most effective method but can be very labour-intensive. Finally, there is the option of using natural predators, though this is still being studied and is not as widely used.
In this article, we’ve outlined six of the most popular Japanese knotweed control methods in order for you to make an informed choice about which method will suit your needs best.
There are several methods for controlling and removing Japanese Knotweed, and which one is used will depend on a number of factors, including:
- the size of the infestation
- whether it is growing among plants and vegetation that you want to keep
- whether it is near a water source
- whether it is on a development site where work must be started quickly
Japanese Knotweed, also known as fallopia japonica, can be controlled and removed by one of our professional contractors. We have years of experience as well as all of the necessary credentials and accreditations to control, treat, and eradicate the invasive weed that may quickly take over an area.
All of our Japanese Knotweed treatment procedures are approved by the Environment Agency Codes of Practice and the Property Care Association, and they will be adapted to your specific needs and the property or area where the Knotweed is growing.
The six most popular methods are listed below.
Method One – Stem Injection
This is an excellent treatment option because it is low-impact and has little risk of disturbing the growth of other plants in the area. Stem injection is typically utilised for lesser infestations, especially where the Japanese Knotweed has established itself among attractive plants or near a watercourse that could become polluted if another treatment is used.
Using a stem injector, we inject an Environment Agency-approved herbicide into the lowest half of each mature Knotweed stem. Younger infestations may not be acceptable since the Knotweed plants must have thick enough stems for the pesticide injection to be effective.
The stem-injection technique used is particularly effective in dry or inclement weather, but the soil cannot be disturbed after the treatment. The stem injection approach is most successful from late summer to early autumn, and it has the greatest impact when the plant is blossoming.
Method Two – Foliar Application
As long as the Japanese Knotweed can be treated across numerous growing seasons, the foliar spray is often the most pursued technique of therapy alongside stem injection. The plants are treated with a herbicide that has been approved by the Environment Agency. Knotweed is sprayed on two or three distinct occasions in the first year, depending on the size of the infestation, and once in future years.
Dry weather is required for foliar treatment, and the soil must stay undisturbed in subsequent years. When the infestation is close to a watercourse, it is not permitted, and it is not the ideal option to employ when the Knotweed is growing among other plants and flora that you want to maintain. The approach works best in the late summer when the weed is blossoming and has the most impact.
Method Three – Weed Wiping
Weed wiping is a simple procedure that, like stem injection, has the advantage of having a modest impact on other nearby plants and foliage, affecting only the Knotweed and not the surrounding flora. The plant’s leaves are cleansed using a sponge that has been drenched in the herbicide. It’s a low-impact therapy that can be employed if the infestation is near water.
The treatments employed are dependent on the size of the Knotweed infestation, and they are not effective for vast regions where it has already taken over. When the knotweed stems aren’t thick enough for the herbicide injection to be successful, it’s commonly utilised instead of the stem injection approach.
Method Four – Bund / Stockpiling
When building on a development site it needs to commence fast and the site is large enough for Knotweed-infested soil to be temporarily stockpiled and treated, the best method to manage this is the bund/stockpiling method.
Bunding or stockpiling is essentially a combination treatment approach of stem injection or foliar application, followed by excavation of the underground material and removal of the soil and material to a separate portion of the site to allow development to begin.
The soil is then stockpiled in a non-critical region on-site that does not need to be built or worked on right away, preferably no more than 500mm thick. The Knotweed is then encouraged to develop in the stockpile so that it can be treated with herbicide later. Procedures are in place to prevent knotweed-infested soil from spreading to otherwise clean portions of the site or from the stockpiling.
This procedure is substantially faster than traditional herbicide treatment methods, saving the developer or landowner a significant amount of time. It can be done at any time while the knotweed’s growth is above ground to identify the infection region, and it’s especially beneficial on construction or development projects to allow work to begin at the original infestation site.
Method Five – Cell Burial / Root Barrier
If there is enough space on-site, a cell burial or the use of a root barrier can be used to avoid the high cost of transporting infested Knotweed soil and debris to a licensed landfill.
The Japanese Knotweed material is buried to a minimum depth or encapsulated and buried within a geo-membrane that can be closer to the surface.
Root barriers can be constructed both vertically and horizontally (usually where there is a concern of cross-border contamination).
If there is enough space on-site to bury or employ a root barrier system for the Knotweed, cell burial or root barrier approaches are applied. Knotweed waste is buried to a minimum depth on-site, and if encased within a geo-membrane, it can be buried closer to the ground’s surface.
If there is a possibility of cross-border contamination, root barrier barriers can be used and erected both vertically and horizontally. Root barriers are utilised to physically control and stop the Knotweed from spreading. If there is a suitably sized area for it to be buried, this method can be employed on both building sites and residential homes.
These strategies are best used on construction sites where building and construction activities must begin rapidly.
Method Six – Excavation and Removal Off-Site
The Knotweed and subterranean dirt are removed and transferred away to a licensed dump site using the excavation and removal process.
Although excavating and removing Japanese Knotweed material off-site is a legal and quick control option with benefits for development sites if done correctly with the right licenses, we are not proponents of this strategy because it poses considerable logistical issues.
When moving Knotweed, there is a considerable chance of it spreading, as well as the cost of transporting the waste to a designated and licensed disposal site.
The Environmental Protection Act (EPA) of 1990 imposes a responsibility of care on those carrying and disposing of Knotweed. We are, however, willing to function as a clerk of the works on a consulting basis if certain requirements are met with the landowner/developer.
Utilising anyone of these tried and trusted methods will come down to your own finances and logistical challenges. If you are still unsure then it is best to reach out to a qualified contractor who specialises in Japanese knotweed removal who will not give you advice but will propose the best method to suit your individual situation.
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