Invasive Species Management

As part of our environmental commitment, our expert teams are trained in the removal and management of invasive species. Both Japanese Knotweed and Himalayan Balsam are an increasing problem and a threat to our native species, they can also represent huge financial burdens for landowners and occupiers. 4th Corner can provide a comprehensive removal and management scheme, which will be tailored to your site and surrounding areas. 

Himalayan Balsam

Whilst complete removal is extremely difficult, our experienced grounds maintenance teams are trained to follow government endorsed procedures for dealing wtih this invasive species.   The species is particularly frequent along the banks of watercourses, where it often forms continuous stands. It can also establish in damp woodland, flushes and mires. Due to its rapid growth, it shades out most of our native species. Each plant produces about 2,500 seeds which fall to the ground, and with several parent plants close together, seeds can occur at a density of between 5000-6000 seeds per square metre. The seeds float, making watercourses a prime route for dispersal of the species. Seeds can also begin to germinate in water on their way to new sites.



Mechanical/physical control
Mechanical control, by repeated cutting or mowing, is effective for large stands, but plants can regrow if the lower parts are left intact. The plant must be cut below the lowest node to stop regeneration. Access to the sides of riverbanks can be difficult and inaccessible stands can quickly recolonise accessible cleared areas, so vigilance is needed if an area is to be effectively cleared. Small infestations (most common in gardens) are easily be controlled by hand-pulling as the species is shallow rooted. To avoid additional spread we do not disturb plants if seeds pods are visible (usually sometime after May). Programmes should be undertaken in April or early May. If hand pulling after this time, we bag plant tops to prevent seed spread.

Chemical control
Himalayan balsam can be controlled by spraying the foliage with glyphosate. The plants are  sprayed in the spring before flowering but late enough to ensure that germinating seedlings have grown up sufficiently to be adequately covered by the spray. Small infestations and individual plants are controlled by using glyphosate in a weed wiper, this has the advantage of preserving native plants and grasses which would otherwise be killed by the glyphosate. The herbicide 2,4-D amine controls many broadleaved annual weeds and may also be used to control this species but is not recommended for use near waterbodies. This selective herbicide may be preferable to glyphosate in situations where the weed has not reduced complete cover of the grasses. A long-lance sprayer is used to assist in the spraying of less accessible areas out of the reach of conventional knapsack sprayers.


4th Corner always follow health and safety procedures outlined by the herbicide manufacturer and take appropriate precautions when working near water.


Japanese Knotweed

Herbicide treatment

The proximity of desirable trees and more importantly any watercourse affect the choice of permissible herbicides.  There are three options with regard to the means of treatment.  The first of which is to apply the herbicide to the leaf of the plant in order that it can translocate through the plant and into the rhizome system.  This method is best performed in the late summer and autumn, the reason for this being that the natural senescence of the plant aids the movement of the herbicide into the rhizome.  Additionally the leaf area is significantly greater at this time of year and as such provides a greater opportunity to absorb the chemical. Stem injection is another means of getting herbicide into the plant.  This involves cutting the stem above a node and then injecting concentrated product into the hollow inter-nodal cavity through the cuticle.  This method can be carried out once the stem has reached a suitable size. Stem cutting, then filling the resultant cavity with a herbicide solution. The cut canes need to be stored on site, allowed to dry and then burnt.


Stockpiling methods

These are used in combination with herbicide programmes. Japanese Knotweed contaminated soil is re-located to another part of the site, spread out into a thin layer (500mm is normally regarded as suitable) and treated following a herbicide programme; a quick and cost effective solution for many development sites. Most suitable for larger sites, where an area of land for the relocated knotweed may be used for several years, while the herbicide programme is undertaken. Costs vary with site, volume of soils to be moved and other factors that will need to be discussed.


Vertical root barriers 

These are used to minimise the risk of an infestation from an adjoining property spreading across the boundary. Other uses of root barriers - are to protect buildings or structures from being damaged – particularly to line foundations if knotweed is in the vicinity. However although vertical barriers comply with Environment Agency recommendations, the Japanese Knotweed Control Company would only advise the use of this method with an appropriate herbicide programme.

Costs of installing root barriers are variable and demand on site visits, discussions and planning. It must be noted that they may need be installed to a depth of nearly 2m (or deeper; one of many factors that will affect final costs).


Reduced level excavation 

This is perhaps one of the most underused methods; simple, adaptable, reliable and suitable in many situations. Essentially a layer of soil (which includes the Japanese knotweed) is removed and taken to a licensed landfill site. The depth of this layer may vary, but may typically be 300mm. Following this removal, a root barrier is placed over the excavated surface and up the exposed sides of the dig out. Excavations adjacent to a building or structure may demand either the barrier to be heat welded to its surface or left in contact. Backfill of excavated areas must only be done with knotweed free soil, aggregate or rubble.

Reduced level excavation is used on large or small areas.


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4th Corner Ltd
Colin Sanders Innovation Centre
Mewburn Road
Banbury , Oxfordshire OX16 9PA
Phone: 01295 817628 01295 817628
Mobile phone 07540 160201
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