Clearing Himalayan Balsam from Nannie’s Water

On 4 June, a fine clear day, about twenty people, led by Amanda Newsome from Natural England and including a large contingent from the Environment Agency, gathered at Blackbury Camp. The stream below the Camp flows through superb valley mires with lots of sphagnum moss, Bog Violet, Heath Spotted Orchid, and Marsh Valerian. Luckily it was usually easy to walk either in or beside the stream; some who strayed into the mire ended up mud-covered!

The aim was to weed out plants of Himalayan Balsam. Although this introduced plant has pretty pink flowers later in the year, it is a serious problem beside many of our rivers and streams, shading out native vegetation and forming almost impenetrable thickets. It is an annual, and the question is: how long do the seeds last? If they are short-lived, then weeding out all the plants each year for a few years should eliminate it because no seeds will be formed. If one starts at the head of a stream then no new seeds can be washed down to replenish the populations. All plants were cleared from the top kilometre of Nannie’s Water in 2007, and a first survey in May 2008 found very few plants, suggesting that seeds do not last for more than a year or two.

The Balsam plants often seem to hide among brambles and nettles so that pulling out every last one can be painful. Young plants of Hemp Nettle and Enchanter’s Nightshade are very similar, so a good eye is needed if innocent plants are not to be sacrificed. Furthermore, for much of the two kilometres or so of stream that we covered, balsam plants were rare, so careful searching was needed. One or two more searches in the summer of 2008 should mean that very few plants remain.

We saw and heard Willow Warblers, Greater Spotted Woodpeckers, and Marsh Tits. Small trout were common in the clear gravelly stream. The artificial pools in the valley held lots of damselflies as well as a single Broad-bodied Chaser. Sadly, though, one of the pools was infested with Parrot’s Feather and New Zealand Pygmy-weed, two other invasive weeds that will prove much more difficult to remove than the balsam.