Himalayan Balsam Invasive Species Control
Bury Water Meadow Group volunteers are making a major contribution to controlling the invasive species Himalayan Balsam (HB). For 5 years over 7km of the Lark & Linnet rivers in Bury St Edmunds we’ve clocked up some 70 volunteer hours annually in surveying and pulling these plants. The scale of the task and nature of the habitat with steep riverbanks and nettles, makes this very labour-intensive work.
With its attractive pink flowers, this waterside-loving plant is invading riverbanks and wetlands so rapidly that scientists are concerned by its negative impact upon the riverbank and biodiversity. It out-competes native plants and increases the risk of soil erosion and flooding.
Don’t be fooled by its pretty flowers or the fact that bees may visit the plant. HB is aggressively competitive and very fast growing – quickly shading out native plants – resulting in a loss of biodiversity by colonising some of our most important riverside sites. HB is so invasive that under the Countryside and Wildlife Act 1981 it is illegal to plant or encourage it to grow in the wild due to both its negative impact on biodiversity and due to the risk of soil erosion and flooding since it dies down in the winter, leaving bare soil. This is because it’s an annual, meaning it grows, flowers, and sets seed all in one season and then dies down in the winter leaving exposed and vulnerable riverbanks. The first shoots can be seen in mid-May and it grows well over head-height by summer. When ripe, the seed pods explode if touched or blown in the wind, shooting seeds into the adjacent river course.
Each plant is capable of producing 800 seeds and once HB is allowed to disperse its high velocity seed, rivers and streams carry it to other sites downstream and so the cycle continues. Prevention is better than cure, so plants need to be cut or pulled before seed is set, which is mid-July to be on the safe side. But the good news is that we have found that where plants are pulled they have returned in much fewer numbers in the following year and so each year’s efforts upstream in the town restricts further spread downstream to Fornham, Hengrave and beyond.
