8 October 2014
Article written by Jack Goode, National Assembly for Wales Research Service
Himalayan Balsam is an invasive weed species which has become increasingly common along rivers and waterways in Wales. Though it was first introduced in 1839 as a cheap alternative to conventionally grown orchids it escaped and spread widely across the UK. It is particularly successful at growing fast and travelling up river basins as it has a particularly aggressive method of seed dispersal in which the bulb explodes and seeds are widely scattered, the balsam also employs pollinators in its incursion owing to its high nectar yields which attract pollinator species away from other native plants. The balsam also grows particularly well where eutrophication has occurred, an issue in some Welsh ecosystems. All of these factors combine to give the balsam a competitive advantage over native species and confirm it as an aggressive invading species.
In Wales the growth of Himalayan Balsams has reached the stage where native ecosystems are being undermined. Current data (fig 1) shows the extent to which distribution of Himalayan Balsam in Wales has reached. Along with draining resources from the ecosystem, the balsam also leads to erosion at the river banks, when it dies in the autumn it leaves soil exposed and destabilises riverbanks. In 2013 the Commonwealth Agricultural Bureaux International, an intergovernmental research agency estimated that there is an annual spend of £300m in Himalayan Balsam Management in the UK as well as indirect costs associated with erosion, and water management. The growth of balsam had also resulted in heavy losses in Spider, Beetle and other insect species.
In order to control the spread of Himalayan Balsam some local authorities in Wales and England have organised “Balsam Bashes” in which vast swathes of Balsam are chopped down and their root systems are removed in order to prevent regrowth. Though this has immediate effect the Environment Agency for England has raised concerns over its long term efficacy and the risk of further seed dispersal from the process. It also may leave areas of uncultivated land more vulnerable to worse invaders such as Japanese Knotweed though the extent of this is currently unknown. Another method which has been found to have a positive impact in the control of the balsam is to reducing eutrophication and ensuring that the riverside habitats are less favourable to the growth of Himalayan Balsam.
Research has been done across 8 sites in Wales to monitor the spread of this weed, its impact on the native ecosystems and the best practise in controlling its proliferation. One particular area of interest in Wales is the River Ystwyth, where Natural Resources Wales has carried out an extensive effort to rid the area of Himalayan Balsam and reverse the effects of this invasive species. The river Ystwyth had four Sites of Special Scientific Interest along its course making this a particularly important area to protect against incursion of the balsam. To remove the balsam, all traces of the plant and root needed to be removed from the soil making this a particularly labour intensive process. The plant material then needs to be left to ensure it dies before being removed from the site. This has meant that though the project for the river Ystwyth began in 2009, by September 2013 only a total of two thirds of the proposed area had been covered.
To avoid this lengthy process research has been undertaken looking at the Himalayan balsam and in its native Himalayan environment to find a method of Bio-control. These studies discovered Puccinia komarovii, a natural rust fungus which is a parasite of the plant; it causes a drop in the vigour of the balsam and reduces the competitive advantage over native species. The safety of using this parasite was confirmed by testing with a broad range of native species to ensure they were not susceptible to the fungus and there were minimal side effects. After this, field trials were done in Berkshire Cornwall & Middlesex which provided promising results; DEFRA has since done a consultation on releasing the fungus and deemed the practice safe.