Working in co-ordination with our sister organisation the River Lark Catchment Partnership, BWMG volunteers are making a major contribution to controlling Himalayan Balsam. Building on its previous years efforts BWMG has this year surveyed 7km of the Lark & Linnet rivers in Bury St Edmunds and has so far clocked up some 75 volunteer hours in surveying and pulling this invasive species. Scything or pulling up by the roots effectively kills Himalayan Balsam but the scale of the task and nature of the habitat with steep riverbanks and nettles, makes this very labour intensive work. See photo (left) of cut HB decomposing.
But don’t be fooled by its pretty flowers. This waterside-loving plant is aggressively competitive and very fast growing, invading riverbanks and wetlands so rapidly that scientists are concerned by its negative impact on the riverbank and biodiversity. It quickly shades out native plants, resulting in the loss of biodiversity and even riverbank erosion and flooding. . It does, however, produce nectar which is very attractive to pollinating insects. Bumblebees can be seen nectaring on the flowers, but this is thought to distract insects from visiting native wildflowers which may, in turn, go un-pollinated. Himalayan balsam in an annual, which means it grows, flowers, and sets seed all in one season.
The first shoots can be seen in mid-May and it grows rapidly, often well over head height with a succulent hollow stem – green in spring and turning red as summer progresses. Seed pods are ripe from the beginning of July and these explode when touched or are knocked by the wind, shooting up to 800 seeds, five metres or more, sometimes into a water course. This will carry the seeds downstream to germinate in the spring some distance from the mother plants. The first frosts of autumn cause the plant to die back but the seed is viable to start the life cycle again the following spring.
Sometimes there is an explosion of plants one year where there were none the previous year. Himalayan balsam is so invasive that, in UK law, it is illegal to plant or encourage it to grow in the wild. Being listed in the Countryside and Wildlife Act 1981, is not enough to stop the balsam advance. Prevention is better than cure, so plants need to be cut or pulled before seed sets. The good news is that our survey has shown that where we pulled the plants last year they have not returned and so this year’s efforts upstream should restrict further spread downstream to Fornham, Hengrave and beyond.