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Improving lives by solving problems in agriculture and the environment

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 plant pathogen that exclusively attacks Himalayan balsam, which can be released into the UK to control the plant while leaving indigenous species intact.

Project Overview

So, what's the problem

Himalayan balsam (Impatiens glandulifera) has rapidly become one of the UK’s most invasive weed species, colonising river banks, waste ground and damp woodlands. It successfully competes with native plant species for space, light, nutrients and pollinators, and excludes other plant growth, thereby reducing native biodiversity. As an annual, Himalayan balsam dies back in the winter, and where the plant grows in riparian systems this can leave river banks bare of vegetation and liable to erosion. Dead plant material can also enter the river, increasing the risk of flooding. 

Like most introduced plant species Himalayan balsam arrived in the UK without any of the natural enemies that help keep the plant in check in its native range (the foothills of the Himalayas, India and Pakistan). Without these natural enemies, Himalayan balsam is able to grow more aggressively and has a greater ability to reproduce, giving it an advantage over native species. Traditional control methods are currently inadequate in controlling Himalayan balsam in the UK. This is often because the plant grows in inaccessible areas or sites of high conservation status where chemical and/or manual control is not an option.

What is this project doing?

The ultimate aim of the project is to find a co-evolved insect or plant pathogen that exclusively attacks Himalayan Balsam, which can be released into the UK to control the plant whilst leaving indigenous species intact, so that the ecosystems can be restored.

Since 2006, surveys have been conducted throughout the plant’s native range to identify natural enemies that could be considered as biocontrol agents in the introduced range. Many of the natural enemies, both fungal and arthropod species, collected and identified during the survey have been rejected as suitable control agents. We undertook safety testing procedures in our UK quarantine facility, and found they were able to attack other closely related to Himalayan balsam.

One natural enemy, a rust fungus, which was observed causing significant impacts on Himalayan balsam in the Indian Himalayas, was exported to our quarantine facility in the UK in 2010 to undergo extensive safety testing. The rust, a Puccinia species, is an autoecious, macrocyclic (completing its entire life cycle on a single species), five spore staged rust fungus which infects the stem and leaves of Himalayan balsam throughout the growing season.

Watch a photodiary of the 2008 survey:


We have tested the safety of this Himalayan balsam rust following strict internationally recognised testing procedures. We compiled a test plant list comprising 84 entries; this consists of 74 species and an additional 10 varieties of three widely grown ornamental species in the UK. There are 26 UK-native plant species, 52 ornamental plants, three economically important crop/ fruit species and three introduced/ invasive species on the list.

Through our research under quarantine conditions we clarified the lifecycle of the rust, thus proving that all spore stages observed on Himalayan balsam in the native range belong to the same species. We have backed up this research with molecular evidence.

Interestingly, through research conducted in the UK, it turns out that the rust species we collected on Himalayan balsam is new to science, and we therefore plan to rename the rust species following the International Code of Nomenclature.

We have now completed all of the safety testing and shown that the rust is highly specific to Himalayan balsam. We have compiled all of the scientific research into a dossier (a Pest Risk Assessment (PRA)) which we submitted to UK regulators for consideration.

Read two recent research papers: 


The team

Project Manager

Staff image of Robert Tanner

Robert Tanner  Senior Scientist - Weed Biological Control

Bakeham Lane
United Kingdom
T +44 (0)1491 829097

Project team

Staff image of Richard Shaw

Richard Shaw

Country Director CABI UK/ Regional Coordinator Invasives Regional Coordinator

Staff image of Carol Ellison

Carol Ellison

Theme Coordinator, Invasive Species Management

Staff image of Sonal Varia

Sonal Varia

Project Scientist

Staff image of Suzy Wood

Suzy Wood

Scientific Support

Staff image of Kate  Pollard

Kate  Pollard

Project Scientist

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