Japanese Knotweed Treatments

Our surveyors can advise the best treatment solutions, plans & costs.

As no two Japanese knotweed-contaminated sites are the same, treatment starts with our surveyors visiting the site to establish the most appropriate treatment or removal method in accordance with our management plan.

Treatment may involve the use of more than one of the recognised Japanese Knotweed treatments, including: –

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 solution depends on various important factors. For example, if there is no building work planned in the near future and there is no urgent requirement to have the Japanese knotweed removed, then treatment can often proceed by means of a Herbicide Application Programme (HAP) alone. Most lenders are willing to release mortgage funds on the basis that the (new) owner (or, in some cases, the vendor) undertakes to complete a HAP, and the programme is carried out as necessary.

Southwest Knotweed are qualified to provide the following treatment solutions:

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

Herbicide Application Programme (Economical Treatment Option)

A variety of herbicides can be used to treat Japanese knotweed. The most cost-effective treatment is to spray the foliage of the knotweed plant with those chemicals which are permitted for use on Japanese knotweed. Treatment typically has to be repeated for several years before the knotweed is effectively controlled, since the rhizomes can still be viable for a period of time.

Japanese knotweed treatment will occur between April and September and will involve at least two applications each season for a minimum of three years. This will be followed by monitoring visits.

The Herbicide Application Programme offers treatment to on-site knotweed with a recognised suite of herbicides applied over three consecutive growing seasons. Evidence of dieback is usually seen following the first application in year one.

Excavation and Landfill Disposal (This Process Can Be Very Costly)

Where time is of the essence, e.g., a developer wishes to proceed with development and would incur costly delay if works did not commence immediately, a combined spraying and mechanical JK removal approach is usually the best option.

The ideal process is to apply herbicide a few weeks prior to mechanical removal in order to allow the herbicide to penetrate the root system as thoroughly as possible. Excavation to a depth of 3 to 5 metres and lateral excavation around any remaining knotweed sites to allow for spread.

All knotweed rhizomes must be removed and taken to a duly licensed facility authorised to take knotweed waste.

The carriers for all waste must be duly licensed, as must the landfill sites, and correct transfer documentation should be obtained.

This Japanese knotweed removal process is far more costly than a chemical treatment.

In some cases, geomembranes are placed to line the area to ensure that if there are any remaining rhizomes, the spread is contained and does not lead to any further spread.

Strictures for biosecurity must always be followed, including:

Wash down of all vehicles in a designated area
Wash down of footwear
Wash down of overalls
Fencing of knotweed area and marking it off, especially in public areas
Assessing the risk of areas where JK might spread
Monitoring the waterways in relation to JK spread

Be warned that even a piece of rhizome the size of your fingernail, or 0.7 grams – an incredibly small piece can result in an entirely new plant. Even after mechanical removal, it is highly recommended to monitor for any regrowth and follow up with spraying that may be required.

Japanese Knotweed Treatments

Our surveyors can advise the best treatment solutions, plans & costs.

Which Japanese Knotweed Treatment Option is the Right one?

Herbicide Treatment:

Pros:

Cons:

Knotweed Stockpiling:

Pros:

Cons:

Knotweed Screening:

Pros:

Cons:

Rhizome Fragmentation and Cultivation (Including Crown Removal):

Pros:

Cons:

Knotweed Burial:

Pros:

Cons:

Root Barrier Installation:

Pros:

Cons:

Licensed Landfill Sites:

Pros:

Cons:

Herbicide Application Programme (Economical Treatment Option)

Excavation and Landfill Disposal (This Process Can Be Very Costly)

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