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As its name suggests, Japanese Knotweed originated in Japan. It was introduced into the United Kingdom by Victorian gardeners in the early nineteenth century as an ornamental plant. In its native habitat, where it is under intense competition from other native plants, Japanese Knotweed usually only grows to around 12 to 18 inches in height. Those Victorian gardeners soon discovered however, that freed from competition, that Japanese Knotweed could quickly lay waste to large areas of land and indigenous plants. Unfortunately, before the menace of this plant was realised, it had escaped into the wild and is now a huge, expensive problem all over the United Kingdom. There are also three other varieties of Japanese knotweed present in the United Kingdom; Fallopia x bohemica, compacta and sachalinensis. Though they vary in height and leaf shape etc from Fallopia japonica, they still look very similar. The methods of eradication and control are the same for all varieties. The following information is intended as guidance only and is mainly aimed towards private householders though much of it is relevant to developers as well. Seek professional advice before attempting to eradicate and dispose of Japanese knotweed.
Description of Japanese Knotweed
The aim is to kill the extensive rhizome system. This can take as long as three to five years. There a are number of methods used to control and eradicate Japanese Knotweed.
Cutting or Pulling
Pulling up the stems is not recommended because of the risk of pulling up part of the crown, which can then re-grow. Cutting can kill Japanese knotweed after a number years through exhaustion but this method is very labour intensive and time consuming.
Geotextile material
The infected area is cleared of infected topsoil and a heavy geotextile layer is laid over the cleared area and covered with new topsoil. The disadvantage of this method is that if there is any damage to the geotextile layer then Japanese knotweed can re-emerge. A site treated in this way must be monitored for a number of years because Japanese knotweed can remain dormant for long periods of time.
Chemicals
The most commonly used weed killer is Glyphosate. This weed killer is applied to the foliage by painting the leaves or spraying them or injection into the stems and is passed within the plant to the underground parts. Please note: Wear the appropriate safety clothing when handling chemicals.
Cut away the old stems during the previous winter to allow good access. The most effective time for spraying with Glyphosate is at the flowering stage in late summer, but this is difficult because by this time the knotweed would have grown to around 7 feet. A more practical method is to allow Japanese knotweed to grow to 3ft, usually by May, and then spray. There will be re-growth and a second application in mid-summer will be required. Check again during September and if it has grown, spray again before growth begins to die back in the autumn. Check again the following spring. Glyphosate-treated knotweed will usually produce small-leaved, bushy re-growth between 20-36in in height the following spring. This differs in appearance to the normal plant and it is important that this re-growth is treated as well.
The problem with spraying Japanese knotweed is the risk of harm to other plants and can be impractical in areas of high conservation value. Another method of using Glyphospate to treat Japanese knotweed is to cut off the stems and apply the chemical in a crystal or liquid form down into the stems. Though stronger solutions of the herbicide are used with the following method, 5 to 1 as opposed to 50 to 1 for the spray method, less is used because far lower amounts per stem are applied.
Combined methods
Digging and herbicide. The surface is excavated to a depth of one foot and the crowns and rhizomes gathered into a pile. Further excavation is carried out to a depth of 2 feet and the pile of crowns and rhizomes are spread over the area. This stimulates the Japanese knotweed to grow a greater density of stems making it more vulnerable to herbicide. With this method it is possible to kill the knotweed in one season using only 2 or 3 applications of herbicide.
Poor man's guide to treating Japanese Knotweed
It can be difficult for the layman to obtain the professional equipment that is normally required to combat Japanese Knotweed. In these circumstances a little imagination and improvisation is needed, hence this section's title of the 'Poor man's guide to treating Japanese Knotweed'.
First of all, the following equipment is required;
How to do it
Put on the overalls and gloves to avoid any direct contact of the Glyphosate with the skin.
Undo the top of the retail bottle of glyposate and pour it into the second container. Remember that you will probably have to tip the second container when refilling the syringe, so make sure it is suitable for the job.
In preparation for cutting the stems, the plastic or a close weave cloth sheets should be laid out for the cut stems to be put on with no risk of contaminating the ground that they are on.
Cut the Japanese Knotweed just above the first node and lay the cut stem on the sheet. Quite often, the first node can almost be at ground level, cutting two to three inches above but still below the second node can make the injection of Glyphosate easier.
Using the thin flat blade screwdriver, pierce down inside the stem through the first node. This will expose the crown to the glyphosate.
Fill the syringe to 5ml to 10 ml from the container and inject the Glyphosate into the cut stem.
After filling the stem, wrap the small plastic squares over the stem opening an secure in place with a small rubber band. This serves the dual purpose of protecting the treated stem from the rain and to mark the stems that have been treated.
If all the stems are cut down it can sometimes be difficult to know how successful the treatment has been until some time has passed. One way to monitor the treatment's success is to leave a stem uncut and untreated. Choose a stem that is one of a number that has grown in a clump. If the application of Glyphosate has been successful, signs of browning at the top of the stem should appear around 10 to 14 days.
The younger and smaller growth that have stems that are too thin to inject should be painted or sprayed with Glyphosate.
When the treatment has been completed, pack up all chemicals and equipment and store them securely away from children. Gather up the cut stems, taking care to avoid them having any contact with the ground, and bag them up. These stems should be allowed to completely dry out and then burnt.
Continue monitoring for new growth and paint or spray this when it reaches a height of around two to three feet. Pay attention to the periphery area of the infection as the rhizome growth is likely to have spread to several feet.
In the United Kingdom, the Wildlife and Countryside Act 1981 made it illegal to spread Japanese Knotweed. This places a responsibility on the land owner to eradicate Japanese knotweed on their land; there is not an option to ignore the problem. All contaminated material must be securely bagged or covered during transport. If Japanese knotweed is to be disposed of off site, only licensed waste operators are allowed to dispose of the material.
The Environmental Protection Act 1990 Section 34, places a duty of care on all waste producers to ensure that any wastes are disposed of safely and that a written description of the wastes, and any specific harmful properties, is provided to the site operator.
Control of Pollution (Amendment) Act 1989 states that "it shall be an offence for any person who is not a registered carrier of controlled waste, in the course of any business of his or otherwise with a view to profit, to transport any controlled waste to or from any place in Great Britain"
The responsibility of domestic householders will be to contact the relevant authorities or contractors that are qualified to treat Japanese knotweed and dispose of the contaminated material safely. The best approach is to inform neighbours of the problem if the contamination is also a threat to their land, and seek advice from the local authority and any environmental agencies.
Gary Hollands March 2005
