Edgmond Wildlife Group (EWG)
Report on Himalayan Balsam Control 2020
by Paula Doherty
Himalayan Balsam is a highly invasive annual plant species that has escaped from garden cultivation and is now prevalent across the UK. It is often thought of as an invader of the banks of water courses, but it also spreads easily across anywhere there is undisturbed reasonably moist soil. It grows up to about 2.5m and can form dense stands that smother less vigorous native plants. Prolific numbers of seeds, up to 800 per plant, are dispersed by exploding seedpods that flick them up to 7m away.
The presence of Himalayan Balsam along the Strine had been observed for several years, but it has recently spread beyond the banks of the stream threatening areas of wild native vegetation. Members of the Edgmond Wildlife Group were concerned to see this spread and approached the landowners to offer volunteer labour to clear the Balsam.
Starting on 18th June and working through until 18th October, volunteers put in 245 hours of their time to control the Balsam. The maximum number of volunteers we had on any day was 13, the minimum was one. The work was spread over a total of 33 visits. Almost all the infestation was to the west of the bridge over the Strine, however several brief visits to the east side removed a growing problem in amongst the new trees.
What did we learn?
Weedkiller would not have worked.
Most effective clearance requires full removal of plants including the roots. This involves simply pulling the plants. Sometimes snapping them into two will help ensure they don’t continue growing.
In large stands they can be slashed but this must be done at ground level otherwise they will re-grow.
Given half a chance they re-root and carry on growing very well, so piling up into heaps or leaving them somewhere to dry out is advisable.
The most effective time is before they flower or set seed.
Plants continue to germinate and emerge throughout the growing season so repeated visits are important.
Once the plants are flowering its best to snap off the flowering parts and pile them up into heaps to ensure they don’t get fertilised.
If the plants have set seeds they can still be gently pulled and crushed before leaving somewhere where any resultant seedlings will be easily spotted the following year.
Whilst removing plants from the riverbank was satisfying, it wasn’t the best use of time. We can only hope to hold the invasion back to the bank. As things stand at present there will always be plants that grow and set seed on the banks of the Strine. The best strategy here is to regularly ‘top’ them to keep their height down so that they don’t flick their seeds too far inland.
The attention to detail over the many hours of work was important. Plants as small as 10cm can still flower. Plants that managed to seed before we found them were plotted on a map for special attention next year.
At the start of the project, it took something like 100 hours to work through the whole area. By the middle of October, the whole area could be cleared in 5 hours.
We will request both landowners to allow us back onto their land next year to continue the task.
It is envisaged that fewer hours will be needed to control the Balsam.
Earlier access will help. Perhaps from early May.
EWG would like to thank the landowners for allowing access to prevent the further spread of this invasive species. Finally, a big ‘thank you’ goes to the determined volunteers without whose efforts this project would not have been possible.
Paula Doherty 14th Dec 2020
(Amended Report 21st Jan 2021)