Biological control of Himalayan Balsam

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.

Results so far

We have tested the safety of the Himalayan balsam rust following strict internationally recognized testing procedures. We compiled a test plant list comprising 69 entries; this consists of 56 species and an additional 11 varieties of three widely grown ornamental species in the UK. There are 14 UK-native plant species, 35 ornamental plants, three economically important crop/fruit species and four introduced/invasive species on the list. To date, we have tested 95% of the test plants in fully replicated and controlled experiments to ensure that the rust only attacks Himalayan balsam. 

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 are now completing the safety testing research, and compiling all of the scientific research into a dossier (a Pest Risk Assessment (PRA)) which will be submitted to UK regulators for consideration.

Project reports

Himalayan Balsam Flyer
Himalayan Balsam News

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