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Non-native species in the UK

A number of non-native invasive species have become established in the UK and are having significant negative impacts on our environment, our economy and our daily lives. Some of the most stubborn invaders are plant species, such as Japanese knotweed and Himalayan balsam - which are often found by rivers - and the aquatic menaces, floating pennywort and Australian swamp stonecrop.


Closeup of a budding and dark pink blossoming Himalayan Balsam or Impatiens glandulifera plant on the waterfront of a creek in a Dutch The CABI stand at the Chelsea Flower Show 2017

What can be done?

Conventional management approaches are failing to stem the spread of these non-native plants. So, the UK government, in partnership with devolved administrators and with the support of a wide range of stakeholders, has funded CABI's research into biological control as an alternative, cost-effective and sustainable management option.

What is biocontrol?

In their native habitats, plants are kept in check by the natural enemies with which they have evolved. When introduced to a new habitat or 'range' without these natural enemies, some plants can thrive and spread, becoming invasive.

Classical biological control - or biocontrol - aims to redress this imbalance. It is the use of specialist living organisms to control pest populations, in this case invasive plants. By screening the most damaging natural enemies from the invasive plant's native range and releasing them as biocontrol agents into the invaded habitats, the plant's harmful impacts can be lessened in an environmentally safe, long-lasting and cost-effective way.

As a result of CABI's work in biocontrol, the UK became the first EU Member State to test and release biocontrol agents. This century-old approach has proved highly successful around the world. Its benefits have already been reaped in the UK's rivers and canals where Azolla - the floating fairy fern - is being successfully managed by the accidental introduction of its natural enemy, a small weevil that only feeds on Azolla.

More questions on biocontrol are answered on the frequently asked questions page.

The species

Find out more about CABI's biocontrol work on five species in the UK.

Donors and partners

Defra (Department for Environment, Food and Rural Affairs) is a UK government department with responsibility for safeguarding the natural environment, supporting the food and farming industry, and sustaining a thriving rural economy. While only working directly in England, Defra works closely with the devolved administrations in Wales, Scotland and Northern Ireland, and leads on negotiations internationally. Since April 2011, Defra in partnership with the devolved administrations and other donors has been funding specialist science to investigate the scope for biological control of invasive, non-native aquatic and riverside weeds posing a threat to native habitats and local economies in the UK.

The implementation of individual projects has also been supported by a wide variety of partners and collaborators and we gratefully acknowledge all sponsors who have contributed to CABI's UK biocontrol initiatives.


Support has come from a wide range of organizations both UK-based and international. Those who have sponsored over £15,000 include:

UK donors

Banister Charitable Trust; Canal and River Trust; Dŵr Cymru Welsh Water; Environment Agency; Ministry of Defence; National Lottery Heritage Fund; Natural England; Natural Environment Research Council; Natural Resources Wales; Scottish Natural Heritage; South East Water; South West Water; Southern Water; Thames Water; Wessex Water; Yorkshire Water

International donors

British Columbia Ministry of Forests, Lands, Natural Resource Operations, and Rural Development; Consortium of Dutch funders* administered through the Dutch foundation STOWA (Stichting Toegepast Onderzoek Waterbeheer); European Agricultural Fund for Rural Development (through the Water Environment Grant); United States Department of Agriculture (USDA) Forest Service

Prior to 2011, research was supported by the Welsh Development Agency, Scottish Government, Environment Agency, Network Rail, Cornwall Council, the Regional Development Agency of South West England, Canal and River Trust (formerly British Waterways) and USDA Forest Service.

* Waterschap Brabantse Delta, Hoogheemraadschap van Delfland, Den Haag, Waterschap Hunze en Aa's, Gemeente Amsterdam, Amersfoort, Watershap Zuiderzeeland, Watershap vellei en veluwe, Watershap vechtstromen, Watershap Rijn en Ijssel, Waternet, Watershap Rivierenland, Rijkswaterstaat, Ministerie van Verkeer en Waterstaat, Waterschap De Dommel, Watershap Drents Overijsselse Delta, Hoogheemraadschap van Rijnland, ProRail, Watershap Limburg, Appeldorn, Waterskip Fryslan, Watershap Aa en Maas, Hoogheemraadschap Schieland and Krimpenerwaard, Hoogheemraadschap De Stichtse Rijnlanden

The devolved administrations

In partnership with Defra and other donors, the Welsh government has been supporting UK biocontrol initiatives particularly the release of the Japanese knotweed psyllid and the Himalayan balsam rust.

The Scottish government initially provided funding during the early research phase of the Himalayan balsam project. More recently, the Scottish government has supported field releases of the Himalayan balsam rust in Scotland, with the releases taking place in 2020.