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Main | Just 12 days until our Famous Five event - have you reserved your time slot? »

Robert's Hogweed Journey with the Water of Leith supported by Baillie Gifford funding

Robert Engstrom Hogweed Hunter
I started volunteering with the Trust early in 2016, attending a few river clean-ups and making a contribution to the success of that year’s duck race by preparing Swedish delicacies for sale and knocking lazy rubber ducks downstream with a wading pole! Over time and through Charlotte I got to know more about the Trust’s work on invasive plant management. She expressed concern about using herbicide near the watercourse as she knew it was toxic for aquatic organisms, and wanted to investigate alternatives – especially for treating giant hogweed.
At the time she had been spraying giant hogweed with herbicide for a few years, without noticing any significant reduction in its presence along the river. Furthermore, Edinburgh Council’s Parks and Greenspaces Maintenance Team, who deals with invasive plants on the river downstream of the visitors centre, had recently started looking into ways of reducing their herbicide use. Hearing this, and being an environmental student with Edinburgh Napier University at the time, I suggested we make a proper scientific research project of it, and managed to get some of my lecturers on board: Jay Mackinnon and Rob Briers.
It all kicked off in April 2017, when we surveyed the river from the visitors centre and upstream until we could no longer find any giant hogweed, using handheld maps and GPS devices to mark out spread (dispersal) and population density. More about plant numbers and distribution and what the fieldwork entails can be read about in a recent article by Edinburgh Live. To decide on treatment alternatives we researched ‘more natural’ herbicides (bioherbicides) and different manual methods of removing all or part of the plant, and at different growth stages. The difficulty, however, is to get to the relatively large and deep-growing taproot: other herbicides than glyphosate will not kill it off, and if you cut the plant down you have to do it several times before new shoots stop coming up. Therefore, the alternative treatments we ended up with were a reduced herbicide concentration, or to cut through the taproot a minimum of 10cm down and uproot the plant.
Treatment days have usually been organised in group, with a core group of dedicated volunteers and students, but the fieldwork also includes revisiting the sites to record treatment efficacy and impacts on associated plant communities, and this has mostly been done through lone working by me. Last year I received a grant from the Botanical Society of Scotland for the hours put in, and this year WOLCT were able to employ me part-time over the summer, after getting the go-ahead from Baillie Gifford to allocate some of their funding donated towards invasive species management.
Findings are very early-stage but it appears using ¾ of the recommended glyphosate concentration is as efficient in killing giant hogweed, and although digging takes longer it appears to have less of an impact on associated vegetation, which in turn could minimise risks of riverbank erosion and make it more difficult for new giant hogweed plants to establish. Plant community data have not yet been analysed, so this statement is just based on observation. The treatment efficacy data has a lot of variation in it, so we need to collect more of it to get a clearer picture of any significant differences between treatments. The study is aiming to continue for at least another 2-3 years before we publish our findings.
 Robert Engstrom  @riparianrobert

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