"Himalayan balsam was first introduced into Britain from the western Himalaya region of Asia in 1839.

It is a tall plant growing to a height of between 2-3 metres and is a prolific seed producer.

Flowers are large and colourful, usually purple-pink or white. They are particularly attractive to pollinators such as bumblebees due to the copious amounts of nectar present in their short, bent spurs.

These flowers are lovely to look at and are great for bees but there's a down side, they are taking over the riverside habitat and dense stands are shading out smaller native plants.

This is worrying as the River Wye is a Site of Special Scientific Interest and its riverbanks support a diverse community of native plants, including several nationally rare and scarce species such as wild chives Allium schoenoprasum.

Our survey looked at the wild plant populations close to the town of Builth Wells in Powys.

But what we really need are yearly plant surveys from the source of the River Wye to its sink.

This will help us to monitor the spread of Himalayan balsam along the riverbanks and establish 'important native wild plant areas for protection.

The spread of Himalayan balsam is so rapid and widespread that any attempt at a complete eradication is going to need many volunteers working in partnership with Environment Agency Wales and other conservation bodies.

More information can be found in Natur Cymru, the Nature of Wales, Number 32, 2009.

Article by Dr Elisabeth Harris of Builth Wells.