Japanese Knotweed Treatment Solutions, Plans & Costs

Our surveyors can formulate and advise the best method of Japanese knotweed treatment for your specific situation

Residential or Commercial Japanese Knotweed – We Have the Solution

As each Japanese knotweed site is unique, treatment starts with our assessors, who will visit the site to determine the appropriate course of action for treatment or removal in accordance with our management plan. This could involve the use of more than one of the proven Japanese Knotweed solutions, such as: –

  • Herbicide Application Program (HAP)
  • Stem injection
  • Dig & dump (landfill)
  • On-site burial
  • Cell burial
  • Root barriers (Geo textile membranes)

Which Japanese Knotweed Treatment Option is the Right one?

The treatment plan used can depend on certain key factors for example; if there is no immediate construction planned or any urgent pressing need to remove the Japanese Knotweed then it can be controlled with a Herbicide Application Program (HAP). Some lenders are quite happy to lend funds for mortgages as long as the purchaser, or in some cases the vendor, has made a commitment, and a HAP is in place and will be carried out. Southwest Knotweed have the experience and knowledge to carry out the following options:

Herbicide Treatment:

Pros

  • Cost effective
  • Treatment can be carried out in situ without risk of spreading the plant further
  • Quickly reduces the capacity of the plant to spread on/off site
  • Quickly eliminates the capacity of the plant to impact built structures
  • Easy to administer

Cons

  • Can take many years to achieve acceptable results, especially where stands are mature
  • Management plans that rely solely on herbicide treatment must include at least 2 years of monitoring after all evidence of growth has ceased
  • Herbicide treatment alone should not be recommended on sites with future development plans that involve the soil being dug and disturbed
  • Construction works cannot continue in areas still containing the plant and the risks associated with landscaping treated soils, e.g. stimulating regrowth, should be made clear to the client and mitigated for
    The use of some herbicides is restricted near waterbodies and desired vegetation
  • Some herbicides can persist in the soil
  • If soil is disturbed at a later date, regrowth can occur
  • Effective control requires expert knowledge of herbicide treatment of Japanese Knotweed
  • Soil which contains Japanese Knotweed that has been treated with herbicide is still classed as controlled waste if it enters the waste stream
  • Herbicide treatment can induce temporary dormancy

Knotweed Stockpiling:

Pros

  • Cost-effective
  • Site work can be undertaken while treatment takes place elsewhere on-site

Cons

  • Requires an area that can be left undisturbed for several years
  • Soil from a stockpile must remain on the site
  • The same cons as herbicide treatment apply in the stockpile area
  • Plant material can be accidentally spread e.g. after a change in ownership
  • The depth of the stockpiled soil must be appropriate for the future use of the soil
  • Rhizome buried deeper in a bund is less likely to express itself and may become dormant; as such, bunds should be created a shallow as is practical and should not exceed 0.5m
  • If larger bunds are created, it may be necessary to apply for planning permission

Knotweed Screening:

Pros

  • Can be cost effective but not always
  • Less material needs to be disposed of to waste facility
  • The treated soil can be re-introduced on site as fill or in soft landscaping areas
  • Where soil needs to be imported, less is required from elsewhere to fill voids created by excavation

Cons

  • All screened soil is still classed as controlled waste
  • Small fragments of Japanese Knotweed will still be present in the soil and could lead to re-infestation
  • Area where screened soils are re-used must be monitored for regrowth
  • Follow up herbicide treatment or manual removal may be required
  • Plant material can be accidently spread during movement
  • Soil type and makeup dictate if it can be screened or not

Rhizome Fragmentation and Cultivation (Including Crown Removal)

Pros

  • Increases the leaf surface area to rhizome volume ratio
  • Breaks up and aerates the soil
  • Can increase the effectiveness of herbicides under certain scenarios
  • Can improve the potential for eradication on sites where the Japanese Knotweed is persistent
  • Crown removal removes a large amount of surface and underground biomass

Cons

  • Most above ground vegetation must be cleared, even desirable plants
  • Cleared vegetation would usually need to be disposed of
  • A large area must be dug to ensure all rhizome containing soil has been included
  • Rhizome located deeper in the soil may be missed and result in regrowth
  • Soil should be compacted at the end of the treatment to help reduce the potential of deep soil rhizome regrowth
  • Crown removal can be time-consuming or impractical for large infestations and removed crown must be managed appropriately

Knotweed Burial:

Pros:

  • Does not require a set-a-side area for control
  • Work can continue immediately after burial
  • Quickly removes the Japanese Knotweed from an undesirable area

    Cons:

    • Restrictions remain on the site, e.g. in some areas deep excavation would interfere with buried material
    • The use of the area above burial site is limited
    • Typically requires a large hole to receive material, so it may not be possible if soil is shallow, or water table is high
    • The appropriate environment agency must be notified
    • Plant material can be accidently spread during movement

    Root Barrier Installation:

    Pros:

    • Can be installed to reduce the chance of horizontal and vertical rhizome spread
    • Can be used to protect structures, hard surfaces, and services
    • Work can continue immediately after installation in areas protected by membranes

      Cons:

      • Tears in the membrane or poorly sealed seams between sheets can be exploited by growing rhizome
      • Can only be installed in favourable weather conditions
      • Damp and/or wet conditions and/or work surfaces will reduce the robustness of heat welded seals
      • Surface drainage and underground water can affect installation and ponding can occur, all of which must be taken into consideration
      • Installation of root barrier is a form of control/prevention to be used in conjunction with other methodology, as it is not in itself a method of eradication

      Licensed Landfill Sites:

      Pros:

      • Quickly removes the Japanese Knotweed from an undesirable area
      • No restrictions left onsite
      • Work can continue immediately after removal
      • Fast and efficient

        Cons:

        • Relatively expensive
        • Disposal to landfill reduces valuable landfill capacity and needs haulage (which damages the environment and increases the risk of Japanese Knotweed spreading) and in the long term unsustainable. As such, disposal to landfill should only be considered as last resort when Japanese Knotweed cannot be suitably disposed of on-site

        Spraying or Stem Injection with Herbicide (Lowest Priced Treatment)

        There are a number of herbicides that can be used to treat Knotweed. Spraying the foliage (leaves) of the plant with a license for Japanese Knotweed chemicals is the most cost effective and efficient method. It does however take several repeated applications over several years to be entirely effective. The rhizome or roots can remain viable for several years.
        Japanese Knotweed treatment normally takes place between April and September with a minimum of two, preferably three, applications per year over at least three years. This would be followed by monitoring visits.
        The HAP involves treating the Japanese Knotweed on site with a selection of appropriate herbicides at regular intervals over the next three growing cycles. – Although you will see signs of deterioration after the first application in year one.
        The overall time to control the plants depends at what time of the year the first application of the programme is made. In total we offer a three year treatment programme (six systemic herbicide treatments in total) followed by two years monitoring with a visit each year, further treatments applied if required.

        Digging & Taking to Landfill (THIS CAN BE VERY COSTLY)

        When time is a major factor, such as when a developer wants to build on a site where delays will add significant costs to the project, then spraying and mechanical Japanese knotweed removal solutions are usually the solution, for when time is a factor.
        The best method is to spray the affected area several weeks prior to mechanical removal to attempt to get herbicide into the root system.
        The area affected should be excavated to a depth of three to seven metres laterally around any stand of Knotweed, to allow for the spread of the root system.
        It is essential that all Knotweed rhizomes are removed from the site and carefully transported to an approved licensed site that will accept Knotweed. Throughout the whole process only approved licensed transport companies should travel to approved licensed landfill sites, which can provide the correct official transport notes to show disposal. Japanese Knotweed removal costs in this fashion are substantial when compared to the costs of chemical application.
        In some case Geo Membranes will be used to line the excavated area to prevent the spread of any remaining rhizomes.
        With all Japanese Knotweed work, BIO SECURITY must be applied including:

        • All equipment washed down in a designated area
        • Footwear cleaned
        • Overalls cleaned
        • Japanese Knotweed fenced off and signed (mainly public areas)
        • Pathways of spread (risk evaluated)
        • Water Courses

        Japanese Knotweed rhizomes can grow into a new plant from a piece as little as you little finger nail or 0.7 grams in weight – That’s really small!!!!!
        Even after mechanically removing the Knotweed it is advisable to continue to monitor the site and be prepared to spray for re-growth.