Himalayan balsam (HB) (Impatiens glandulifera) is another highly invasive plant which has very successfully managed to spread from gardens into the wild across the UK. HB is an annual plant that reproduces from seed. It has a very effective mechanism for spreading its seed; its seed pods pop in sunny weather or when touched, spreading the seeds by up to 7m. It is a highly invasive plant capable of dominating river banks in a ribbon of pink flowers in late summer.
HB is viewed by many as an attractive plant and its high pollen productivity makes it a favourite of bee-keepers. These desirable qualities have no doubt hastened its spread but it is not a natural part of the flora on the banks of the Spey, nor any other UK river. Once established the dense stands tend to dominate river banks, out-competing native plants and when it dies back in the winter it leaves bare river banks susceptible to erosion.
As it is an annual plant it can be controlled by a variety of methods including strimming, hand pulling, chemical spraying, grazing etc. Seed viability is relatively short in the UK, up to two years so effective control programmes will soon result in reduced abundance. It should be noted that any chemical applications within 10m of a watercourse will require a SEARS licence.
Further details about Himalayan balsam control methods can be found on the Invasive Species Scotland website.