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Improving lives by solving problems in agriculture and the environment

Invasives species in Great Britain: case study

Invasives species in Great Britain: case study

Invasive species, such as non-native weeds, animals and microorganisms, are a major issue. They are one of the main causes of biodiversity and economic loss and are impacting on human health and livelihoods. These problematic species affect all types of ecosystems and are a global problem. In Great Britain, economic losses caused by the weeds are huge.

Japanese knotweed by road

Demonstrating the cost of invasive species to Great Britain

Invasive Non-Native Species (INNS) can have a detrimental effect on biodiversity, crop production and livelihoods across the world, and Great Britain is not exempt. This case study highlights some of the most troublesome invasive species in Great Britain and what they are costing the country.

japanese knotweed

£1.8 billion per year - the economic impact or invasive species

Up until recently, there was no official figure for the toal cost of controllling Invasive Non-Native Species (INNS) in the UK. So, a survey was commissioned across England, Wales and Scotland which found that in 2010, the cost of efforts to ericate these invasive species amounted to £1.7 billion. By now it would be £1.8 biliion. These results are important as they highlight the imprtance of addressing INNS in a way that is effective, efficent and sustainable.


Rabbits and Japanese knotweed are most expensive to control 

Japanese knotweed is notorius for being one of the worst Invasive Non-Native Species (INNS) and costs the UK Government over £165 million per year to try and control. Overall, rabbits are the most expensive pests to control, costing the UK over £263 million every year. Currently, the Government is spending millions of pounds a year in unsustainable ways of controlling invasive species, highlighting the need to invest in biocontrol methods. 


Early eradication economically beneficial 

It is easier and cheaper to eradicate invasive species while they are still in the early stages of establishing themselves. Also, due to a usual lack of natural enemies, these Invasive Non-Native Species (INNS) often get out of control and cause damage to property, flood defense systems, public roads and carparks. The cost of controlling these species is much lower when they are controlled before they spread and cause damage.

Japanese knotweed is deemed to be one of the worst invasive species in Great Britain. The only effective method of controlling it was to use strong chemicals, however this method is unsustainable and is costing over £165 million a year. A scientific team from CABI led research to find a psyllid (Aphalara itadori) which feeds soley on Japanese knotweed. By feeding on the sap found in the stem of the plant, the psyllid helps to control the spread of Japanese knotweed.

More recently, CABI released a rust fungus as part of field trials to control the non-native, invasive weed Himalayan balsam (Impatiens glandulifera) using natural means. 

Himalayan balsam is an environmentally damaging weed and its large scale control is virtually impossible. The rust fungus is a novel solution to control this pervasive weed.

Here's a video about the invasive weed and our research


Unsustainable methods of controlling non-native species, such as manually removing them or the use of pesticides require heavy investment. This work means that the same measures are used year after year, to try and control invasive species in the same areas, at great cost to the taxpayer.

Himalyan balsam covering a river

Risk of flood damage

As well as this, many weeds thrive in marshy conditions and so often spread rapidly over riverbeds, only to die back in the winter. This comprimises flood defenses as well as increasing the amount of debris in rivers.

Floating pennywort invasion UK

Harm to livestock

Equally, animals that graze near infested water often mistake weeds such as floating pennywort (the 6th most expensive invasive species) for grass. They then try to graze on it and can often drown. This can become very expensive for farmers if they keep needlessly losing livestock because of uncontrolled INNS.

For more information on invasive species, take a look at CABI's invasive species compendium.

Biological control of Himalayan balsam

Himalayan balsam has rapidly become one of the UK’s most invasive weed species. A lack of natural enemies allows it to successfully compete with native plants for space, light, nutrients and pollinators, reducing biodiversity and contributing to erosion. Traditional control methods are inadequate. This project involves identifying an insect or... >>

Controlling floating pennywort in a safe and sustainable way

Floating pennywort is an invasive aquatic plant that can over-run water bodies in the UK, and is threatening habitats, native plants, fish and insects. Also a problem across much of Europe, this plant has rapid growth and can regenerate from small fragments. Management is mainly limited to mechanical clearance which is expensive and often... >>