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An Indian rust fungus has been released at several sites across England as a form of 'biocontrol' - using a natural enemy to control an invasive species, in this case the Himalayan balsam.


Introduced by Victorians as an ornamental plant, the Environment Agency now estimates that the Himalayan balsam occupies over 13% of river banks in England and Wales. It can reach over 3 metres in height and causes trouble by smothering vegetation, out-competing native plants and by adding to the risk of flooding by clogging waterways.


This week, the not-for-profit organisation CABI released the rust fungus in Berkshire, Cornwall and Middlesex after successful laboratory trials showed that it causes significant damage to Himalayan balsam but does not impact on native species.


The wet Bank Holiday weekend was a wash-out for some, but as Museum botanist Dr Mark Spencer explained, it was the perfect conditions for release: "the fungus does best in warm, wet conditions!"


Know your enemy


Dr Spencer has been advising on the project, which is headed by CABI with primary funding from Defra and the Environment Agency, and with contributions from Network Rail, the Scottish Government and Westcountry Rivers Trust.


Himalayan balsam.jpg

The Himalayan balsam, dominating the banks of the River Alt.

© Mike Pennington


The rust fungus, a natural enemy of the Himalayan balsam in its native lands in the foothills of the Himalayas, has been extensively tested as a natural control method. Conversely, using existing methods, the Environment Agency estimates it would cost up to £300 million to eradicate Himalayan balsam from the UK.


Selection of a suitable natural enemy and laboratory trials took eight years. If the rust is successful in the UK, Dr Spencer predicts it could resolve the problem of Himalayan balsam within a few years.

This is a really important step forward for the control of invasive species in Europe, I wholeheartedly support the decision to approve release. Project partners have already set up a monitoring programme to assess the spread of the fungus onto Himalayan balsam. If the fungus establishes itself at the trial sites there should be no need for additional releases, the fungus will spread naturally through the UK.

The licence to release the rust fungus is only the second of its kind ever issued in the UK, following the 2010 release of a specialist insect, Aphalara itadori, to control the plant Japanese knotweed.


Read more about invasive species in the UK:

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