Bio-control of Himalayan balsam

Balsam riverbankAfter eight years of research in quarantine, field trials are currently underway on the introduction into the UK of a biological control agent of Himalayan balsam (Impatiens glandulifera) using a species of rust native to the Indian sub-continent, the original home of balsam. The rust causes plant growth to distort and warp, with stems bending and toppling over, opening them to secondary infections. Although it does not eradicate balsam, the loss of vigour will give native species the opportunity to re-establish themselves, restoring a natural balance.

Following this year’s trials in three locations (Berkshire, Cornwall and Middlesex) innoculated plants will be introduced to more sites next year. After that natural spread of rust spores, which lie dormant in infected leaf litter over winter, should do the rest.

Balsam flowerHimalayan balsam is a decorative annual non-native plant originally indroduced to the UK as a garden plant. Unfortunately it spreads rapidly through seed, has few native controls in the UK, and rapidly crowds out native plants to the extent that the Environment Agency estimate that it is now present in more than 13% of riverbanks in England and Wales. As with Japanese knotweed, spreading Himalayan balsam is an offence under the Wildlife & Countryside Act 1981.

(For more information including a NNSS factsheet and ID guide, click on an image.)

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