Chemical Treatment

The most common and sustainable method of treatment for Japanese knotweed is through the use of herbicides. There are several products on the market that can be used to combat knotweed and they have varying degrees of effectiveness, as well as differing impacts upon the surrounding land and vegetation.

At present, there is no single product legally available in the UK capable of killing 100% of all Japanese knotweed with only a single application (unless the growth is extremely weak). Whilst an impressive result can be obtained by the first application, provided it is applied at the optimum time of the year, further re-growth will usually occur during the following year(s) Because it is necessary to kill off all of the plant’s extensive rhizome system, knotweed eradication can take several applications over a prolonged period of time. Treatment through purely chemical means takes, on average, three to four years (and occasionally longer).

Residual herbicides can kill off the knotweed’s top growth and any rhizomes growing close to the surface. Once in the soil the herbicide forms a chemical barrier, preventing rhizome at deeper levels from sending new shoots to the surface. This can give the appearance above ground of total eradication, though the viable but dormant rhizome tends to reappear once the ground is disturbed or the chemical barrier breaks down over time. As such, the results obtained from these chemicals can be misleading. There is an important place for residual products in the treatment of Japanese knotweed, though dependence upon them alone is inadvisable.

When planning a treatment programme Wreford consider:

* Proximity of Japanese knotweed to watercourses and lakes
* Sensitivity of other species of vegetation growing in the vicinity
* Size of the infestation and density of the stand
* Proximity of tree roots if using residual herbicides
* Proximity of badger sets or other forms of protected wildlife

This enables us to determine the best choice of herbicide and the best method of application (knapsack sprayer, stem injector gun, weed wiper, etc.)

The use of combination techniques can speed up the timescale required for using herbicides. Click here for more information. Wreford can also offer an ‘advance and treat’ system that applies non-destructive methods to herbicide control, which can increase the effectiveness of treatment over a shorter period of time.

There is a substantial amount of legislation concerned with the use of pesticides. Examples include the Control of Substances Hazardous to Health Regulations (COSHH) 1988 and the Code of Practice for Using Plant Protection Products 2006. The control of pesticide regulations can be found within the Food and Environment Protection Act (FEPA) 1985. It is also a requirement that any intention to apply any herbicide within 5-10m of a watercourse must not be carried out until written confirmation has been received from the Environment Agency.

The application of any pesticides should only be carried out by contractors with a recognised National Proficiency Test Council (NPTC) Certificate of Competence. This ensures that the right herbicides are used and applied correctly. It is an offence to use non-approved products or to use approved products in a manner that does not comply with the specific conditions of approval. All Wreford staff are appropriately trained and conform to the set legislation.