Warm weather causes outbreak of Japanese knotweed

09 Jun 2016


Japanese knotweed

This year, forecasts are predicting a very warm summer, and with it reports are out of Japanese knotweed taking hold earlier than usual. Japanese knotweed costs the British economy an estimated £166 million per year.

In addition, almost £11 million being spent on battling the plant along our road networks and waterways alone (source: http://www.cabi.org/). Originally native to eastern Asia and China, Japanese knotweed was first introduced to Europe in the 19th century as an ornamental plant. This fast-growing, invasive plant is adaptable to a wide range of climatic conditions and can cause devastation for developers and home owners alike, growing through asphalt and concrete - damaging buildings, bridges and roads.

Once Japanese knotweed is established, underneath or around a built environment, it can be very difficult to control. Early identification allows developers to assess and cost options for destroying, disposing and managing it. The Environment Agency has created the knotweed code of practice which offers different methods of managing Japanese knotweed, and advises on alternative ways to treat it on site in order to avoid creating a waste disposal problem. This is intended to reduce landfill and haulage needs (and their associated cost), and the increased risk of spreading the knotweed. 

Tips for developers

  • Always check the site you are buying for Japanese knotweed. Whilst this shouldn't necessarily stop the purchase of the site, it will affect how profitable a development could be, and the timeframe in which it can be built. If there isn't Japanese knotweed on the site, consider getting legal guarantees that confirm this before purchasing the site.
  • Create a timetable for Japanese knotweed treatment and development. If knotweed is present, then ensure enough time is allocated within the development timescales and apply a Japanese knotweed management plan.
  • Managing previously treated Japanese knotweed areas. Knotweed may have been buried on-Site or taken to landfill, or alternatively chemically sprayed or injected by appropriately qualified contractors, who should be members of INNSA. However, just because the development site has been treated doesn't mean that Japanese knotweed may not grow again.

Read more about our Ecology and invasive weed services.