Invasive Non-Native Species Management - Environment Agency

We are currently undertaking a fifth year of Yorkshire-wide, main river non-invasive treatment of Giant Hogweed, Japanese Knotweed and Floating Pennywort. The ever-expanding programme is the largest catchment-scale invasive non-native species management project in the country. This work is being carried out on behalf of the Environment Agency and supported by other partners such as Yorkshire Wildlife Trust, Yorkshire Water, Canal and Rivers Trust and other local organisations.

We carry out 3 phases of treatment between April and November each year alongside multiple site specific Floating Pennywort treatments. Currently the programme covers all main rivers within Yorkshire with the exception of the River Derwent and River Colne which are supported by the Yorkshire Wildlife Trust. Our teams are all NPTC qualified operatives and treatment is carried out through handheld and boat-mounted sprayers.

Phase 1 refers to the early season treatment of Giant Hogweed (Heracleum mantegazzianum). Giant Hogweed poses a risk to public health through toxic sap, and can spread rapidly throughout river systems. Phase 1 is undertaken between March and May each year which coordinated updates produced to the Environment Agency and partners.

Phase 2 covers a second linear pass of all main rivers, this treatment takes place between May and July. Phase 2 targets any re-growth of Giant Hogweed and any immature late season plants which may have been missed during Phase 1. In this month we will also begin treatment of Floating Pennywort (Hydrocotyle ranunculoides) which again, will be targeted across 4 phases culminating in November.

Phase 3 is carried out between August and October each season and focusing entirely on Japanese Knotweed (Fallopia japonica). All mature stems and accessible Japanese Knotweed plants are individually injected at the stem. Difficult access or dense populations are initially sprayed until stem injection becomes a viable option.

This is a reoccurring treatment programme funded by the Environment Agency which is evaluated annually on its success and viability. In 2018, we surveyed over 450 km of watercourse throughout Yorkshire for invasive weeds, with the aim of recording and reporting what is growing, and where. This provided guidance to the Environment Agency on the scale of management resource needed in subsequent years.

In 2022, we have actively surveyed and treated over 1200km of watercourse in Yorkshire and continued to make efficiency savings for the Environment Agency to enable more cost-effective treatment across the catchment.

‍