A Background On Japanese Knotweed
Japanese Knotweed is a variety of invasive plant species that grows quickly and can cause environmental damage if not controlled. In urban environments, unchecked growth can damage pavement and foundations.
It can also cause drainage problems and mineral depletion when growing wild. When beginning a new project or redeveloping an area, it is important to be on the lookout for Japanese Knotweed and to take mitigation steps if it is found.
You can identify Japanese Knotweed by its stalks, which resemble bamboo, and by the purple and red speckles found on its leaves. The plant has pale flowers during August to October and can grow as tall as two to three meters.
How a Construction or Development Company Should Handle an Infestation
The Weeds Act of 1959 and the Wildlife and Countryside Act (1981) dictate how to handle Japanese Knotweed when it is discovered. Before clearing a site for work, construction and development companies should inspect the area for any Knotweed plants. In some geographical areas, an ecological survey may be required as part of the development planning application. Even if a formal survey is not required, hiring an Environmental Consultant can save you money in the long run.
If the plant is found, it will be necessary to develop a plan for control or eradication. Japanese Knotweed rhizomes can extend under the soil for up to seven meters away from the furthest plant colony. Disturbing a growth can encourage the plant to spread, so removal must be handled carefully.
Where possible herbicide treatment is recommended. If the plants must be cut or pulled due to other environmental concerns, extreme care must be taken to make sure that the plants don’t re-sprout and spread further. They should be thoroughly dried on a plastic sheet or a built wooden platform, but never on the ground.
Once dried, the Knotweed plants must be properly disposed of. This can be achieved though deep burial on-site or by covered transportation to a licensed landfill site. Contaminated soil should also be disposed of in this way. Japanese Knotweed is designated as controlled waste, and disposing of the plant improperly is punishable under the Environmental Protection Act of 1990.
When leaving a site, workers must ensure that their tools, machinery, and clothing are not carrying traces of Knotweed. Everything should be cleaned thoroughly to avoid spreading the contamination.
- True Eradication: Will Knotweed Comeback?
- What Legislation Surrounds Japanese Knotweed?
- What Damage Can Knotweed Really Do? A Handy FAQ
As stated above, herbicidal treatment is often the best way to get rid of Japanese Knotweed. If the plants are near water, the Environment Agency must be consulted before spraying herbicides. The plants should be treated during their growing season, between March and October. After spraying, it may take up to six weeks before the plants show signs of dying.
Plants should be sprayed in the spring before they grow to their full height. For dense concentrations, consider a glyphosate-based herbicide like Roundup Pro Biactive. This type of chemical works by blocking the enzyme system of plants. Land areas that are not near water can also be treated with Imazapyr, Picloram, or Triclopyr.
In areas where the Knotweed is more spread out, a chemical such Dormone (a 2,4-D amine preparation) can be used. Dormone is designed to work on broadleaved plants and will not kill the grass. The downside of this approach is that it may two to three years to entirely kill the infestation. Spraying in early summer and late summer before dieback will help the treatment be successful.
To quicken the destruction process, aboveground leaves and stems can be dug out, making sure to remove all of the Knotweed rhizomes. At least the top 3m of soil should also be removed, in a radius extending 7m out around the infestation. After the plants are dried out, they should be treated with herbicides before burying them to a depth of at least 5m. This method is more labour intensive and expensive, but is a good option when development must move forward quickly.
Construction and development companies must understand their responsibilities under the law when dealing with Japanese Knotweed. Conducting a survey with an Environmental Consultant and working closely with the Environment Agency will help companies meet the regulatory requirements and avoid fines.
If you want more advice on TP Knotweed and how we can remove the dangerous plant, call us on 0800 389 1911 or contact us online.