Himalayan Balsam control along the River Seph
Himalayan balsam is a plant native to the Himalayas and was introduced to Britain by Victorian plant hunters. The first record of it being planted in gardens is 1839.
It can be identified by a pink, slipper-shaped flower which has a sickly sweet smell. It has a hollow stem and can grow up to two metres tall. The exploding seed pods can scatter seeds up to seven metres from the parent plant.
It's often found growing along riverbanks where it rapidly outcompetes our native plants, forming large, dense patches. The seeds remain viable in watercourses and those transported downstream can establish new colonies. The plant is annual so it dies back completely in winter, leaving riverbanks without any stabilising vegetation, making them susceptible to erosion. With more water run-off into rivers the sediments reduce water quality, and spawning areas of salmon and other fish can be smothered and the risk of flooding increases.
A bit of background
Our project began in 2008 following concern over the large amount of Himalayan balsam found along the lower sections of the River Rye. However, as the plant's seeds can be spread via watercourses we needed to start tackling the balsam right at the top of the catchment and work downstream. This meant starting on the River Seph which begins at Chop Gate in Bilsdale and is the main river that flows into the River Rye. The River Seph in turn is formed from the confluence of Raisdale Beck and Bilsdale Beck.
Getting it under control
A survey was carried out in 2008 to map out where the balsam was growing, then in 2009 the control work began on two tributaries - Raisdale Beck and Bilsdale Beck. Local contractors were hired to do the bulk of the control work through a combination of strimming and hand pulling, the local community and volunteers have also helped.
By 2012 we had covered 21km (13.5 miles) of riverbank, taking control work right up to the confluence of the River Seph with the River Rye. We also carried out repeat control work which is necessary due to the presence of a seedbank in the soil (seeds can remain viable for approximately 18 months) and the varying growth rate of the plant. Control work also began along an embankment north of the village of Hawnby which was found to be abundant with balsam. National Park Volunteers also tackled stretches of riverbank on the Rye in Duncombe Park National Nature Reserve, working with Natural England.
The sweet smell of success
The project is now in its seventh year and we are delighted our efforts are proving to be worthwhile. Very little balsam is now being found in those areas previously controlled, and in some areas the balsam has been eradicated. The National Park Apprentices have been working along the River Seph to remove any remaining plants this summer.
Last year, 2013, we were able to extend the control work onto the River Rye and tackle the stretch from the Seph confluence as far down as Rievaulx Bridge, a distance of about six km (four miles). Control in this area is being repeated this year. Please see our leaflet for further details on Himalayan balsam control and how you can help.
Rona Charles, Ecologist