Himalayan balsam - what is it? Why does it matter? This invasive, non-native plant has become widely established along streams, ditches and roads in Devon, competing with native plants for light, nutrients, pollinators and space. It is an annual plant and dies back over the winter to leave riverbanks exposed and vulnerable to soil erosion, causing negative impacts on water quality and wildlife downstream. Thanks to our fantastic volunteers and the Tavistock taskforce, DWT's #UpstreamThinking tea