Himalayan Balsam
Himalayan Balsam (H.B.) occurs in dense stands along the River Otter and in many of the waterways of the southwest. It competes with the natural vegetation and can overwhelm it, causing erosion of the river banks and reducing biodiversity. Available control methods for H.B. are labour-intensive and difficult to implement. The habitats of the plant are often inaccessible. Small-scale operations are generally ineffective and need frequent repetition. Catchment-scale treatments are therefore recommended but are generally impractical and prohibitively expensive.
In its native habitat (the foothills of the Himalayas in India and Pakistan) H.B. occurs at an altitude of around 2,500 metres, growing in clusters of only 30 to 60 plants no more than 1.5 m high and often mixed with the native vegetation. It has various natural enemies, including fungal parasites and insect predators. However, in the U.K. it has no known natural enemies and, since its introduction
as a garden ornamental in the 19th century, it has invaded
and become a major problem of waterways in the south and west of England.