Buttery Business

James Symonds, Project Officer, Scottish Invasive Species Initiative
March 2020

White butterbur (Petasites albus) is a rather lovely plant in many ways. Its white, Hyacinth like flowers are, along with the Snowdrop, some of the first to be seen in the new year and can brighten up those winter walks along our rivers. In summer its plate-sized leaves create an overlapping mat of terrestrial lily pads that catch the breeze and flutter to and fro in a shimmer of white and green, very striking indeed.

White butterbur in flower in late February

However, its delicate appearance belies an insidious nature.

Native to the mountainous areas of Central Europe and the Caucuses it was, along with most invasive non-native plants species, introduced to Britain as an ornamental plant. Its introduction was earlier than most of the headline grabbing exotics like Japanese knotweed, 1683 to be precise, perhaps due to its natural range being so much closer to home. It was recorded in the wild by 1843 and is now firmly established and naturalised across much of Britain, with the North East of Scotland seeing the highest concentrations of plants.

White butterbur is a rhizomatous plant, meaning the plant has a network of roots (the rhizome) underground that are interlinked and plants grow from this root system. When the leaves die back in the late summer the plant puts energy back in to the rhizome where it is stored over winter ready for its early flowering and rapid growth in the new year. This is where its insidious nature starts to become evident.

Exposed rhizomes on the edge of a river bank

Because of the substantial energy stores in the plants rhizome it can grow rapidly as soon as conditions allow. By mid-April early May, just when our native woodland plants are really wanting to get going, it already has a dense mat of foliage covering the woodland floor. This mat completely shades the ground meaning no other plants can access the sunlight so essential for their growth. With little or no competition, the rhizome has enough energy to spread laterally potentially, or eventually, taking over entire woodlands.

Dense carpet of White butterbur leaves on the River Fiddich

As White butterbur prefers deciduous wet woodland, it is very common along the river networks of the North East of Scotland. When the rivers flood and erode their banks, fragments of this rhizome are broken off and washed down stream where they settle and create a new stand of White butterbur and so the plant spreads, eventually taking over entire woodlands along water courses to the detriment of our native flora.

Nowhere have I seen this more evident than on the River Fiddich, a sizeable tributary of the River Spey. From its confluence with the Dullan Water in Dufftown to where it meets the Spey at Craigellechie, White butterbur has become the dominant species along its course. Anywhere that is prone to flooding is a mass of White butterbur and very little else, hectares upon hectares of ecological desert.

White butterbur dominating the river banks

In these areas even young trees struggle to break through the darkness of the butterburs low lying canopy. Trees younger than perhaps 20 years are hard to find raising the question of the woodlands very existence. So what can be done?

There is, in fact, very little research out there on the control of White butterbur so here at the Scottish Invasive Species Initiative we have set up some trial sites to see what works and what doesn’t, you can read more about the details of our trial and findings here.

Early indications suggest, perhaps unsurprisingly, that application of a systemic herbicide is the most effective way of treating the plant. The most effective time to spray it seems to be once the plant is in full leaf, June onwards. At this point the biomechanics of the plant shift and instead of directing energy in to growth, energy is being transferred back in to the rhizome for over wintering, this greatly improves translocation of herbicide from the leaf that is sprayed to the rhizome which is where it is needed! That being said I have treated White Butterbur effectively in late April but these were small poorly established patches.

If your daily exercise is currently taking you for a walk along a river bank keep an eye out for this pretty little invasive (below left) and its cousins, the purple flowered native Common Butterbur, Petasites hybridus (below centre) and the formidable Giant Butterbur, Petasites japonicus (below right) with its more elaborate flower spikes and creamy flowers, the leaves of this one can get to 90cm across!!

Finally – how do you think the Butterburs got their name? Answers on the back of a postcard…

Hogweed munching sheep at work

Al Reeve, Project Officer, Scottish Invasive Species Initiative, June 2019

In an era where people are increasingly environmentally aware and there is a move away from the over-use of chemicals we want to investigate a solution to invasive species control that can be done inexpensively, at low intensity, and with minimal environmental impacts….so, enter the humble sheep!

This trial project by the Scottish Invasive Species Initiative is a practical experiment to discover if a land manager could use sheep to control a substantial giant hogweed invasion. A previous sheep grazing trial, by the Deveron, Bogie and Isla Rivers Charitable Trust at Auldtown (near Huntly) which began in 2013, shows that in a controlled environment, sheep can make light work of giant hogweed infesting a field. (Read the Auldtown Grazing Report). However this new trial is not just about measuring the impact of the sheep on the giant hogweed and woodland environment, but of the real life example of managing the site and sheep from the farmers perspective, recording the successes, failures and lessons learned from the outset.

The new trial site is at Kirkside Farm, Macduff, where we are working in partnership with the Gordon family who farm here. It is a 1km stretch of woodland sandwiched between arable fields and the River Deveron. Giant hogweed has begun dominating the woodland, particularly around the sunnier edges, and along the numerous streams that flow through the wood to the river. In the past, attempts to control the giant hogweed has been via pesticide application using a knapsack sprayer, which proved very time consuming and costly. Due to the scale of infestation and the difficult terrain of the site so far little progress has been made in restricting the giant hogweed’s expansion.

After fencing in the site, in April this year we released 25 sheep into the woodland area, asked dog walkers to keep their dogs on leads and waited to see what happened… and for the first month, nothing did! The sheep lazed around the entrance to the site, maybe due to the new environment or maybe because they had never eaten anything other than grass before.

During this time we started mapping the extent of the hogweed through the site both though ground surveys as well as using drone footage (courtesy of TAHR Media) to visualise the infestation. Working in partnership with The University of Aberdeen we will be monitoring the site and have developed a base map of the hogweed which, after an annual survey, we can compare to. We have also identified 40 monitoring spots where we will measure the effect of the sheep on the rest of the woodland vegetation.

As time went by though, we started to pick up more indications of the sheep growing in confidence with clear trails developing through the wood showing where the sheep had been walking as well as a few nibbled hogweed stems.

Fast forward a couple of months and the sheep have well and truly gained a taste for the hogweed. There are now large patches of much-munched hogweed, a huge change from previous years. It’s worth mentioning here that sheep don’t actually kill the hogweed plants just by chewing on them but by restricting the plants from flowering they are slowly removing the amount of energy stored in the hogweed’s tuberous roots. Hogweed take 3 or 4 years to mature before finally sending out a flower spike to release seeds but by continually grazing the plants sheep can stop the older plants from flowering and mow down new seedlings as they emerge from the soil.

The alternative control method of using a broad spectrum herbicide like Glyphosate results in the killing of the target plant but, however carefully applied, also results in some collateral damage of the other species surrounding it. This has the effect of opening up the soil which enables more hogweed seedlings to germinate and fill the newly cleared space. One of the many benefits of grazing as a control method is that the ground flora is not killed off and this acts as a barrier against hogweed seedlings emerging.

Despite the great work of the sheep this year, there are still some patches of hogweed that have grown too big and dense for the sheep to get on top of and so this first year has not been a complete success, but we’ve learnt a valuable lesson – next year we need to get the sheep on site earlier in the year. However, on a positive note we’ve been delighted by the response of the site users and dog walkers in acting responsibly and the local awareness raising and signage has been a success.

The sheep will stay on site for a few more months and hopefully continue their good work and we can get a fair idea of what their impact has been so far. Next year, we can act on our lessons learned and improve our methodology.

This is a multiple year project and one of the outputs will be to develop practical and useful advice to empower other land managers to use sheep – or other livestock – as a means of controlling invasive plants on their land. This will include public open days and site visits etc. as well as written findings.

This project truly is a work of collaboration and the Scottish Invasive Species Initiative would like to thank all the partners for their continuing support and input; the Gordon family of Kirkside Farm, The University of Aberdeen, the Deveron, Bogie and Isla Rivers Charitable Trust, the Macduff Distillery and the local people of Macduff.