Himalayan Balsam is now a widespread problem throughout the UK. It is mainly found on river banks and areas of damp ground. Where it does grow it tends to colonise densely, therefore supressing the native plants in that area. This not only effects the native plants, but also has a negative impact on invertebrates such as spiders, beetles and bugs which relay on the native plants.
As Himalayan Balsam regrows annually from seed, it leaves large areas of riverbank bare during autumn and winter when the plant has died back. This leaves the riverbanks open for corrosion and potential flooding. The silt from the river banks ends up in the bottom of the rivers having a negative effect on fish spawning sites.
How do we control it?
In order to control Himalayan Balsam effectively, a management programme needs to be put into place. Seed banks last for up to 18 months and therefore a minimum of a 2 year plan should be engaged. If neighbouring land, or there is a water course through the infected area, then a collaboration with neighbours should try to be achieved for control. Seeds will travel great distances in rivers and across field boundaries.
Mowing
Control can be successfully achieved through mowing however certain criteria’s must be achieve.
Access must be good, as bushes and steep riverbanks may make some areas inaccessible
The cut height must be very low, below the first node of the plant, if regrowth is to be stopped. If this is not possible, re-cutting must be carried out regularly throughout the season as the plant will re grow and flower.
Flowering and seed pod ripening occurs June – August, therefore monitoring and cutting must continue until end of August.
Hand pulling
If the areas of infestation is only small, and again access can safely be achieved, then a good option is to hand pull. Young plants are easily pulled up by the roots. Again this should be carried out before the plant comes into flower.
Grazing
Allowing livestock to graze the area can reduce the infestation. This is achieved through grazing or constant trampling. However this is not the most effective measure and total control is difficult to achieve.
Chemical Treatments
A programme of herbicide treatments, if managed correctly is one of the best ways of controlling areas of high infestation. The use of glyphosate products, cleared for used in aquatic situations can be used on river banks. Although glyphosate is a total herbicide, and will therefore terminate all plants that it contacts, this is not usually an issue due to the Himalayan Balsam already supressing other plants.
Where infestation is away from water courses a selective herbicide of 2,4-D amine can be used to successfully control the plant without damaging underlying grasses.
In both cases of herbicide treatments, timing is crucial. An application between April to mid-June, before the plant becomes into flower and seed is important. Continuous monthly checking of the site for any missed, regrowth or fresh germination is needed in order to ensure irradiation.
A 2nd year of treatment will ensure that any dormant seeds from the previous years have been caught. However, following seasons should also be monitored for any imported germinating seeds from neighbouring infestations.