Himalayan balsam on the worth

 ​In the last blog we mentioned a couple of invasive species, mink and signal crayfish, in this blog we will look at another, Himalayan balsam (HB). 
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Himalayan balsam(Impatiens glandulifera, aka Policeman’s Helmet, Jumping Jacks and Bee-Bums) is actually quite a beautiful flower and children love the way the seed pods pop when they are ripe. It is an annual plant, growing from last years seed each year, with a reddish stem it can be seen growing up to 2 metres tall along the river bank and in other damp places. The pink flowers form in June and July and are much loved by bees and bee keepers alike. The seed heads develop in July-August, come the middle of August the heads start to ripen and will explode when touched, dispersing the seeds a great distance. 

HB flowers. See the bees bum sticking out of one of the flowers!

​There are two main problems with HB:

• The plants are very prolific and fast growing so they smother any native species growing nearby thus impacting plant diversity. There are areas along the Worth where Himalayan balsam is the only plant growing. This not only impacts plant diversity it limits it more generally as removing the native plant species means that native insects that rely on those species will also not be present, for instance butterflies, that are often plant specific. It is said that bio-diversity is reduced by 25% when Himalayan balsam dominates.
• The root system of HB is very shallow, this means that in the winter, when the plant has died off and the river floods the bank can be susceptible to erosion. This is a considerable problem on the Aire. 

HB colonising much of the left bank of the river above the bridge at Pit Street. Picture courtesy of John Tickner.

​We have lots of HB on the Worth, so what should we do about it? This is something we have been thinking about at RWF. The main method of eradication for us is, before the seed is viable, to pull it and leave it to compost on the bank (balsam bashing). We have missed the  boat this year as the seeds pods are now exploding. A sensible future strategy would be to start bashing at the highest point of infestation, this will be right at the headwaters of both the Worth and Bridgehouse beck, and work  
downstream. 

Himalayan balsam flowers and seeds on the left, one of the top seeds has just exploded.

It’s no good just bashing it in Keighley because every plant higher up the river can produce up to 800 seeds which can float down stream to re-colonise the cleared area. ​

​The problem is that this strategy requires considerable organisation and a lot of people to work persistently over many years (seeds can remain dormant in the soil for up to three years), resources that RWF do not have. So we are wondering if the war on Himalayan balsam on the Worth may have been lost.

HB taking over!