Tree Management

The Japanese Knotweed plant spreads in a vegetative manner from crowns (like Rhubarb), stems and rhizome (underground root). Small sections of cut stem, crown or roots are capable of growing into a new plant. Since it is a non-native species, there are no UK insects or animals that eat or control it and once established, it quickly takes hold. Controlling spread is therefore dependent on human intervention.

Rhizomes grow rapidly underground and are responsible for the spread of the plant on site. They produce long white shoots which travel underground and then send up shoots to the surface. The roots can travel under concrete and tarmac and push their way up through quite densely packed surfaces.  If soil contaminated with parts of the plant is moved to another part of the site or to another site it will re-grow and spread.

The plant can be sprayed with herbicide or controlled by stem injection in situ. This process is only effective during the growing season and it can take three years or more to completely eradicate a problem. It is important to continue treatment even when the bulk of the problem has been resolved as the slightest overlooked section can be the source of re-infestation.

As all parts of the plant readily regenerate, they must be allowed to dry out after they have been pulled or cut, this is best done on a tarpaulin rather than on the ground and certainly not in a compost heap. Burning the plant on site after cutting and drying, (where current by-laws allow it), can be done provided that the waste is burnt on site and not removed to other land.

Knotweed material is regarded as ‘controlled waste’ and not disposing of it properly would be an offence under the Environmental Protection Act, 1990. Allowing the spread of Japanese Knotweed into the wild is also an offence under the Wildlife and Countryside Act 1981.

Regardless of how it originally arrived, the weed becomes the responsibility of the landowner wherever it grows. As a managing agent, you need to check that any contractor you appoint to control this weed has the appropriate level of skill and knowledge to undertake this work. Where offsite removal is contemplated, check that they have a waste carrier’s license and issue a waste transfer note for every load. You should budget for two visits per year over several years.

Tom Evans is Tree Team Manager with Microbee Ltd