JKSL Features in Environment Industry Magazine
Mike Clough's recent article on Japanese Knotweed was one of the key features in the first issue of Environment Industry Magazine.
To view the latest issue, please click on the link http://www.eimag.co.uk/Home.html
Or, read below for the full article:
New Plants, New Ideas, New Technology.
In the battle for supremacy within the natural world Alien Invasive Plants will definitely always have the upper hand. If you introduce an alien plant such as Japanese Knotweed into a new environment where it has no natural enemies - it will grow to the preclusion of all native species.
Once Japanese Knotweed has established and begun to spread - the alien plants will develop into massive monoculture stands of single species blocks. If you attack the infestation and manage to control the plant then you often will have a secondary problem of potential for erosion or embankment de-stabilisation particularly where the infestation is beside a watercourse.
The spread of Japanese Knotweed has been nothing short of a spectacular environmental disaster. Since its introduction in the 1800’s the plant has spread phenomenally. A recent study cited Japanese Knotweed as being present in every 10 square kilometers in the UK with costs for removal estimated to be in the region of £1.56 billion.
Many of our ‘problem plants’ of today were introduced on purpose by Victorian Gardeners. In simplistic terms the horticulturalists of the era thought themselves ‘masters of the universe’ able to control and manage ‘nature’ to their own ends. They introduced Japanese Knotweed, Giant Hogweed and Himalayan balsam as ornamental garden plants admiring their ease of propagation and rapidity of growth. The gardeners of the time then saw that ‘all nature was a garden’ using false ditches instead of walls to demark their property boundaries. Whilst confined within high walled gardens these plants could be managed and contained – however once introduced into the ‘wild’ their growth simply went exponential.
To create an answer to these problems one must first understand how and why these plants were first introduced and then spread so dramatically. It is in understanding these issues that we will begin to find alternate strategies to control and eradicate them.
New Plants - Japanese Knotweed
The rhizome system is the main part of the Japanese Knotweed plant – extending up to two metres in depth and seven or more metres horizontally. The rhizomes are storage organs containing water, carbohydrates and elements required for stem growth. Energy and compounds required by growing stems are supplied by the rhizome until the stem reaches approximately one half to two thirds of its total height. After this point, photosynthesis products are translocated via the stem to the rhizomes.
Japanese Knotweed spreads through rhizome expansion, fragments of live rhizome or stems. Dispersal of these fragments is provided by for example fly tipping, movement of contaminated topsoil or cutting of stems.
As little as 0.7g of live material is required for propagation. The hollow knotweed stems have internodes at regular intervals all of which have the ability to propagate.
Following invasion Japanese Knotweed typically out competes other plant species by shading our other plants and depositing a heavy leaf litter smothering any germinating seedlings. Using its ability to store large amounts of water and nutrients also reduces the available resources to other plant species.
There are currently no natural diseases or predators in the UK which affect or predate on Japanese Knotweed.
If located on steep banks or waterways invasion by knotweed can lead to soil erosion and damage to flood defences – in addition, knotweed biomass can block watercourses resulting in flooding.
Current common control methods for Japanese Knotweed include the use of a variety of herbicides, digging and removing huge amounts of infested soil to licensed landfill or creating waste management areas within site boundaries. These methods are time consuming, costly, difficult to perform and environmentally damaging.
One of the major areas for Japanese Knotweed spread is on or near watercourses where chemical use is restricted and excavation and removal not possible. Chemical treatments will take a minimum of five seasons with repeat spraying – which in most instances make waterside developments non viable.
Repeat cutting of Japanese Knotweed can lead to its control however this method often leads to the spread of the plant if live material is not handled properly. The response of cutting the knotweed stems is to produce more shoots which emerge quickly after cutting – thus causing more problems. Control through cutting will take at least five growing seasons and is massively labour intensive.
New Ideas - Mapping
The first step to control must be identifying and mapping the scope of the problem - once a base plan has been prepared a strategy can be adopted -what you can measure you can manage.
New technology is helping with this - with new light weight, hand held systems linked in to satellite mapping systems enabling stands of knotweed to be plotted down to the nearest 500mm.
The Cornwall knotweed forum (http://www.cornwall.gov.uk/default.aspx?page=13824) have been using GPS technology for some time now in an effort to control and manage the spread of Knotweed within their boundaries – this should be adopted by all councils throughout the UK to give a comprehensive base point on which future planning and strategies of management can be implemented.
New Ideas – Biological Control
In its native Japan – Knotweed is predated upon by a fungus and a weevil both of which are present only in its native habitat.
Research has been undertaken by CABI Bioscience (http://www.cabi.org/) with regards the potential release of these control agents in the UK.
Whilst the pathogen and insect will both slow the growth of Japanese Knotweed it is understood that they will not kill the plant.
This will be useful in areas where funding is not available for eradication strategies (such as river corridors/country parks) but may well be problematic in development sites. Any standard eradication strategy will typically employ chemical application to foliage – both of the potential predators defoliate the plant (remove the leaf) – thus making foliar chemical application impossible. If chemical application cannot be guaranteed this will push clients towards excavation and removal from site, which is both costly and not environmentally friendly.
New Ideas – Soil Sifting
Control of aggressively growing plants having a rhizome or large tap root is typically difficult to achieve because of the volume of material that needs to be removed from site to ensure that all of the plant root is removed.
Typically Japanese Knotweed can be 70% by mass in the top 400mm of soil going down to 10% by mass at 1.5 metres and down to less than 5% at depths below two metres. However even the smallest fragment of Japanese Knotweed can re-grow to produce a new infestation – thus typically massive volumes of material have been excavated and removed from site.
Current best practice guidelines recommend employing a clerk of works trained in the identification of Japanese Knotweed rhizome to be present on site during any excavations thus reducing the volume of materials taken off site.
A recent strategy employed by Knotweed removal contractors is the use of soil sifting technology – in simple terms - the hand picking of rhizome material from the soil – thus the only material taken off site is pure knotweed rhizome with no soil – again reducing the volume of material taken off site.
New Ideas – Direct Injection
One of the problems with treating Japanese Knotweed with chemicals is actually getting the poison into the plant.
The thick leathery surface of the leaves give a layer of protection which is difficult to penetrate – whilst the underside of the leaf is more susceptible to spray - it is difficult to spray in an upward direction without causing ‘drift’ (when the chemical becomes airborne and causes loss of surrounding non-target species).
A new technique involves the direct injection of herbicide into the plant stem giving a metered dosage into the hollow center of the plant. Alternate strategies involve drilling into the woody rhizome of the plant and applying chemical into the hole – then plugging with coloured markers to show treatment areas.
New Technology – the Japanese Knotweed Solution
Since the massive growth in the treatment of Japanese Knotweed much has been made of new strategies, secret trials, new systems, new chemicals – but nothing actually NEW ever seems to come along.
In June of this year a product will be launched by the leading Japanese Knotweed contractor in the UK – initial presentation will be in Manchester followed by a series of events around the country.
Following several years of trials and close monitoring of the manner in which Japanese Knotweed spreads and its strategies for survival a technique has been produced based on using the plants aggressive nature against itself.
This will be non chemical, environmentally friendly, re-useable and will both prevent erosion and enhance soil stability.
Perhaps at last we will be able to talk about a Japanese Knotweed Solution?
Mike Clough, Managing Director.
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