Japanese Knotweed Treatment and Removal

This excavation and movement of Japanese Knotweed material to an area of the site where it will not be disturbed. Creation of a bund and subsequent treatment with herbicide.

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.

Is the excavation of Japanese Knotweed material and screening (sieving) the material through a mesh or other selective system to remove rhizome fragments, which are then disposed of correctly and safely. The soil that passed through the screener will still be classed as controlled waste and may be used on site but must be located where it will not be disturbed. This soil will then need to be monitored for at least two growing seasons and any regrowth treated with herbicide, or dug out (usually manually), before control can be considered complete.

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.

Digging and breaking up rhizome (underground root system) material and soil with the aim of increasing the leaf surface area to rhizome volume ratio and to un-compact, disturb and aerate the soil. Crown removal can be integrated into such works, including prior to the commencement of herbicide treatment. The subsequent Japanese Knotweed growth is then treated with herbicide.

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.

Excavation of Japanese Knotweed material with burial at another part of the site at an appropriate depth to prevent regrowth. Monitoring of the area will still be required and any regrowth treated with herbicide.

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.

Acts to prevent horizontal and vertical growth of Japanese Knotweed by installing a vertical and/or horizontal membrane barrier. Monitoring of the area will still be required for at least two growing seasons and any regrowth treated with herbicide.

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.

Excavation and transport of Japanese Knotweed material to a licensed landfill using haulage vehicles. Monitoring of the area will still be required and, although all rhizome material should have been removed, any regrowth treated with herbicide.

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.