Friday 16th August, 2019

Himalayan balsam (Impatiens glandulifera) is widespread throughout the Wye and Usk catchments.

This plant was introduced to the UK in 1839. It grows to around 2 metres high and is characterised by its pink flower in late summer and exploding seed pods in autumn.

The problem for rivers is that not only does balsam smother native plants and reduce biodiversity but it also has very shallow roots. This means that when it dies back, there is very little root structure to hold the river banks together, leading to excessive erosion during the winter flows.

Up to now, controlling Himalayan balsam has involved pulling, cutting and spraying but has largely been ineffective. After an extensive project lasting several years, it has almost completely been eradicated from the Monnow catchment. However, such projects are costly, involve a huge amount of effort and have to be comprehensive to be effective.

In 2010, CAB International (CABI) began testing the use of a rust fungus as a control. It was found to be highly specific to Himalayan balsam, not affecting any other plant. In 2014, the balsam rust was approved for release by Defra, the first fungal biological control agent to be released against a weed in the European Union.

In 2019, the Foundation will begin a joint venture with CABI to trial the rust at two locations in the Wye catchment. The initiative is part of our “Restoring Our Amazing River” project, funded by DEFRA’s Water Environment Grant.

The fungus does not kill all the plants but weakens them enough to enable the other forms of management to become effective and viable. The results will be carefully monitored but we very much hope that this will reduce the problems caused for our rivers by this invasive plant.