Damage to brick wall by Japanese Knotweed
within infestations, with growth exceeding 5cm per day. Combine this with the total lack of natural predators, the nice warm climate in this country, together with fertile soil, and the plant can’t stop from spreading. Surely a plant that can
grow this quickly and form massive single species monocultures must have some ecological advantage? Well, as far as my research
has taken me, the only advantage I can see is that the flowers produced in late September and October provide a good source for late season nectar and an interesting flavoured honey, apparently attractive habitat for Badgers due to the rapid growth of the plant and therefore the cover provided, and some use for flower arranging.
The disadvantages of the plant far outweigh the advantages. Structural damage, river bank erosion, damage to underground services, reduction in biodiversity, increased maintenance costs, increased risk of flooding in watercourses and the fact that the dead over winter stems provide a location for accumulating litter and the like.
So we know the problems, the history and the reasons why it spreads so rapidly, but what options are there for controlling the plant, why and how?
Contained within the old
Victorian Gardens, Knotweed provided a good backdrop to Herbaceous Borders, a rapid
Japanese Knotweed is like a vegative iceberg
growing hedge to shield the views of the peasant farmers from the manor houses and the like. A useful plant that posed very few problems and was controllable. Outside of this environment the plant has discovered that it can, and will, spread thereby causing considerable damage as mentioned previously. Methods of control have
taken many many hours of painstaking research and trial and error tests by numerous scientists and private contractors throughout the world. From this research the traditional methodology of long term herbicide applications has been developed. This involves applications of Glyphosate 3- 4 times per year for a period of up to 5 years in order to kill a single plant! Even then, death is not likely to occur, more likely is the fact that the plant will not grow for a couple of years before deciding to come back with a vengeance when you are least expecting it!
Newer methods have been developed whereby
contractors can eradicate the plant within one growing season, some claiming as short a timescale as 12 weeks or so.
Alternative methodologies include removal of vast quantities of soil to landfill sites, installation of protective root barriers or heavy duty black out sheeting. The reason that the plant is
so hard to kill is the fact that it produces a complex and extensive rhizome system underground with rhizomes growing up to 10 metre
length, convoluting their way through the soil to a distance of up to 7 metres from the visible plant to a depth of 3 metres. I personally have seen rhizome growth exceed this on many occasions, but it is very dependant upon the soil type, location and local environmental conditions. Nonetheless the plant is like a vegetative iceberg, and in the back of your mind must be the fact that new plants will regrow from healthy rhizome sections a fraction of a gramme.
Normally being spread
through fly tipping or along watercourses, any
management plan must be long term and must be managed effectively to prevent this plant from taking over. There are numerous sources of advice available on the internet. In fact, this plant is now so notorius that a Google search of Japanese Knotweed within the UK alone will produce over 100,000 results. The information is out there, but care must be taken to chose the correct management plan and ensure that the problem is not made worse. If in doubt ask an expert. New methods of control are being investigated using Bio Controls. Release of this Bio Control agent, developed by CABI Bioscience (
www.cabi-
bioscience.org) is expected within the near future. The intention of this widespread bio control is not to eradicate the plant, but merely to try and stem the spread of it. Numerous other projects
are being undertaken at universities and colleges
Japanese Knotweed can come back when you least expect it
throughout the UK, USA and Australia to look into novel and efficient methods of eradication.
Japanese Knotweed is listed as the Environment Agency’s biggest problem invasive species, control of which was valued at £1.56 billion in the UK alone in 2003. (DEFRA 2003)
IF you think Knotweed is a scary thought, then please take a minute to consider Giant Hogweed (Heracleum mantegazzianium). This gigantic invader,
brought to the UK in the mid 19th Century, has a bite to match its somewhat foreboding appearance! Not to be confused with
Cow Parsley (Common Hogweed), Giant Hogweed has the ability to inflict serious injury to those that come in contact with it or, in some cases, illness by being merely near the plant! Giant Hogweed sap
contains chemicals known as Furocomarins which have an effect known as
Phytophotodermatitis. In short, contact with Giant Hogweed produces blistering on the skin and a reduction in the Melanin present to protect the skin against the UV rays from the sun. Burning occurs rapidly in these areas and the effects may last numerous years with the scars lasting many many years after that.
In worst case scenarios this bllistering can lead to third degree burns and death. As experts in the fields of
grounds maintenance and plant care, we should never
Japanese Knotweed is listed as the Environment Agency’s biggest problem invasive species
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