Zapping invasive plants – a trial on Exmoor

Holly Moser, Exmoor Non-Native Invasive Species Project Officer
September 2021

As many of you may be aware invasive non-native species (INNS) control can take many years and here at Exmoor National Park Authority we have been going at it for the last sixteen! A major part of our work, our knotweed control programme, has been running since 2005 and has resulted in a large reduction of the knotweed species, particularly Japanese and Himalayan knotweed across the National Park.

Each year we seek permission from landowners to treat knotweed using the conventional method of spraying glyphosate. Currently, thanks to the funding, we can offer this service free of charge. Our contractor completes the treatments between September and November when the herbicide is most effectively drawn down into the rhizome system.

Spraying Himalayan knotweed

This autumn we will be visiting 95% of the 850 plus knotweed sites we can treat using glyphosate, probably the highest percentage ever achieved on the programme! This may sound a lot but many of these sites are being monitored and may no longer need treatment because there is no visible growth showing. It is vital that we continue to monitor these sites because knotweed rhizomes can stay dormant underground for something like up to ten years, which means shoots can sneakily reappear!

On Exmoor there are several knotweed sites we cannot treat with herbicide because they fall on organically certified land and we have not found a suitable “organic” alternative to glyphosate treatment. This land provides a serious reservoir for invasive species to flourish, particularly where a plant is situated close to a watercourse allowing them to spread easily. There is also a lot of controversy surrounding the use of glyphosate as a herbicide and the future of its application is uncertain. So it is crucial that we expand our toolkit of methods to control INNS and find solutions for control on organic land.

In 2017, we began trialling Rootwave Pro which has proved to be very effective on annual weeds and was first trialled on Japanese knotweed in 2016 in Gloucester, by the Environment Agency. This technology forces an electric current of up to 5000 volts down through the plant, raising the temperature and boiling the plant cells. It’s very dramatic to watch – lots of steam and popping and banging! The plant is left to decompose, and you can see the effects of the treatment within a few weeks. I have to admit it is satisfying watching a plant which is causing so many problems and is so difficult to get rid of, turning yellow and wilting without the use of herbicides to treat it.

The Rootwave machine. You rub the electrode up each stem for approximately 30 seconds. It is a very dramatic treatment with lots of steam, popping and banging!

How are the trials going so far?

In 2017 and 2018 the National Park commissioned Ubiqutek, the manufacturers of Rootwave Pro, to carry out one treatment a year on five knotweed sites. It soon became clear that one treatment a year might not be enough because the knotweed continued to throw up lots of little shoots.

Left: 2017 – Japanese knotweed before any Rootwave treatments took place.
Right: 2018 – after a single treatment in 2017.

Luckily the project was able to use our new funding to purchase our own Rootwave Pro so that we could continue these trials and increase the frequency of treatments. We were also able to train up several local contractors to operate the machine. So we can now carry out up to three treatments a year on 28 different sites including other INNS: American skunk cabbage, giant hogweed and montbretia.

Although we have made great progress carrying out multiple treatments a year it has not been smooth sailing…

There are several factors to consider when using Rootwave Pro:

  • First the location. The machine needs to be transported to site on the back of a 4×4 or ATV due to its size and weight and you are also limited to a 27 metre long treatment cable from the vehicle. Although we would not expect to find knotweed on some of the most remote parts of Exmoor this has been a limiting factor for us. The technology is however adapting quickly and who knows how long it will be until Rootwave can be carried on your back…
  • Secondly, it cannot be operated if it is raining. On Exmoor this is a challenge, especially with the wetter summers we are now experiencing. However wetter ground is better for conducting electricity so if your operator is able to drop everything and fit in a couple of hours when the rain has stopped then rainy days don’t have to be a write off.  Having the flexibility to change plans and carry out a treatment when the time is right is definitely a bonus!

Of course, we have also had to deal with the elephant in the room which is affecting everyone. Busy schedules and short time windows impacted by the pandemic and combined with the British weather have not made it easy for our contractors. The result is that we have struggled to complete three treatments a year at all of our sites as we had first planned.

What results have you seen since you started the multiple treatments?

It’s important to point out that we are only in our second year of multiple treatments and the very early stages of this trial, but despite all the challenges things are looking quite promising.

It’s clear that every site has reacted differently to each treatment as you would expect when there are so many factors like competition from other species, ground substrate and moisture content in play. In our first year of multiple treatments, some of our knotweed sites continued to show vigorous growth. This is to be expected – invasive species, by their very nature, are tough to control.

Left: May 2020 – young Japanese knotweed appearing before Rootwave treatments took place.
Right: September 2020 – two months after the second treatment of the year.

Other sites looked more positive with less regrowth appearing. At this site (image below) our contractors reported only a handful of stems after its first ever treatment.

Left: August 2019 – before any Rootwave treatments.
Right: August 2020 – two months after its first ever treatment.

We have also seen similar results over the years at the sites that were first treated in 2017. Below you can see a comparison of two sites that received a single treatment in 2017, 2018 and 2019 and two treatments in 2020. These photos were taken in September. Both sites are yet to receive a treatment this year which makes a good comparison to September 2017 when the sites hadn’t been treated at all. Again, some sites have continued to show quite vigorous regrowth (top two images); while at others the difference is more obvious (bottom two images).

Two Japanese knotweed sites treated using Rootwave – single treatment in 2017, 2018 and 2019 and two treatments in 2020.
Top left: Site 1 before (Sept 2017), Top right – Site 1 after treatments (Sept 2021)
Bottom left – Site 2 before (Sept 2017), Bottom right – Site 2 after treatments (Sept 2021)

For our other species it is a similar story that multiple treatments for several years looks like it could be the way forward. We were however delighted to see that one of our skunk cabbage sites, where there was a single plant, does seem to have disappeared for the time being after its first year of multiple treatments.

Left: June 2020 – a single skunk cabbage plant before any Rootwave treatments.
Right: June 2021 – after two treatments in 2020.

So we are seeing some interesting results in the early stages and these trials are playing an important role in broadening our options for INNS control. Like any trial, there are always lessons learnt to be passed on and we have definitely had our fair share. Check our website for updates as our trials progress and please do get in touch if you have any questions.

Tel: 01398 322259

Email: ennis@exmoor-nationalpark.gov.uk

The Exmoor Non-Native Invasive Species (ENNIS) project is trialling innovative approaches to invasive species management and working with the local community to map and control invasive non-native species such as Himalayan balsam, American skunk cabbage and American signal crayfish. If you would like to find out more about the project please follow this link to our ENNIS website.

The ENNIS Project is funded by the European Agricultural Fund for Rural Development and Defra.

Flying, Flinging and Floating – Seed dispersal by Giant hogweed and Himalayan balsam

Vicky Hilton, Volunteer & Communications Officer, Scottish Invasive Species Initiative
September 2021

Here at the Scottish Invasive Species Initiative our invasive plant control seasons for giant hogweed and Himalayan balsam have now drawn to a close and thousands of plants have been sprayed, cut or pulled – removing these pesky plants for another year and critically preventing seeding and spread.  However, that’s not the end of the story.  In the soil lie dormant seeds: snoozing silently but waiting their chance to germinate.  And beyond our control areas are plants which are now about to do what they do best – scatter their seeds for future germination.

When it comes to invasive plants seed production and dispersal is usually significant and impressive – the ability to reproduce quickly, and in numbers, is one trait that makes these invaders spread successfully and be worthy of the status of ‘invasive’.

Plants have limited mobility and rely upon a variety of dispersal methods to transport their seeds, and so reproduce, away from the parent plant.  Seeds are more likely to survive away from the parent plant – they can reach habitats favourable to survival and with less competition and larger distance seed dispersal can allow plants to colonize altogether new geographical areas.

Giant hogweed and Himalayan balsam are both highly mobile species – they are good at seed dispersal and spread readily to new areas.  While this makes good evolutionary sense for the plant in ensuring its survival and success as a species – for those of us working to stop the spread of these species it certainly brings challenges.   

Understanding how these species disperse their seeds and how long these seeds persist in the soil helps enormously with the planning of control work.  For example, both these species use flowing water as a dispersal mechanism – meaning that control work needs to start with the most upstream plants in a river catchment. Treating plants downstream first would be futile as seeds from those upstream plants will wash down and re-infect cleared areas. 

Giant hogweed

Giant hogweed plants flower only once after growing for 2-5 years (longer if conditions aren’t ideal).  After seeding the plant dies.  Although that might give hope of successful control, in reality if the plant sets and spreads seed then the damage has already been done. A single flowering plant will produce between 10,000 – 50,000 seeds, with 20,000 seeds per plant being typical – and each seed can remain viable for many years. 

The dry flattened oval seeds are produced at the end of August.  Each is approximately 1cm in length with brown lines extending about three quarters of the length.

As the seeds are shed from the towering 2m high seed heads their winglike membrane allows them to be caught by the wind and dispersed over short distances (2-10m).  As they drift away from the parent plant they often fall into a river or burn where the water can carry them long distances to new areas.  Studies have shown that giant hogweed seeds can float for up to three days – in that time seeds could be moved huge distances in normal flows and even further in flood events.

Humans can also give a helping hand and be responsible for spreading giant hogweed seeds.  This can be accidental e.g. when seeds are caught and transported on vehicles or in shoe treads – or via transportation of seed contaminated soil.  

If seeds land on a suitable area of ground (there is usually plenty along a riverbank) they will settle into the soil and overwinter to allow maturation and breaking of dormancy.  Germination occurs from January to March with approximately 90% of seeds successfully germinating. Those seeds that don’t grow in the first year can lay dormant in the soil – the seed bank – for many years.

The consequence of this seedbank means that control works will need to be repeated on the same site for several years until the seedbank is depleted and the site truly clear of hogweed. Viable hogweed seeds have been recorded up to seven years after seeding occurs.  This reflects what we witness in the field – we have sites new to the Scottish Invasive Species Initiative where after control for four consecutive years, we still see significant regrowth of seedlings each year.   However, at sites where control has taken place for six or seven years (by previous and the current project) we see significant decreases in annual seedling reoccurrence giving hope that we are closer to achieving hogweed eradication in some locations.

Himalayan balsam

Himalayan balsam is an annual plant with a cycle of growing, flowering, seeding and dying all in one year. As such its survival from one year to the next depends entirely on successful seed production – so prevent the seed production and you remove the plant. 

Balsam seeds are produced in a seed pod, or capsule, which hangs on a long stalk alongside the flowers. The kite-shaped green pod is 2-3cm long and 8mm wide and contains on average 6 seeds per pod (between 4-16 seeds can be present).  The small round seeds are initially white, turning black as they dry.  On average 700-800 seeds per plant are produced.

When it comes to seed dispersal – balsam is the master.  It uses ballistic seed dispersal – exploding seeds pods – to forcefully fire the seeds up to 7m from the plant.  The seed pods are dehiscent – meaning that when mature they will spontaneously explode at the slightest disturbance. The capsule splits along the longitudinal edges – which are built in lines of weakness in the pod – firing out the seeds as the sections curl back.

These expelled seeds are often carried by humans – unintentionally caught on clothes and picked up in shoe treads – and there have also been observations of seeds being transported locally (up to 10m) by small rodents.  But mostly the spread of balsam seeds is aided by flowing water – fresh seeds can be transported within the sediment of riverbeds – particularly during the high flows present during flooding.  The dry seeds are buoyant and can float over large distances in the water currents – before being dropped into new areas to successfully colonise and continue their spread.

Himalayan balsam seeds also have a high germination rate – approx. 80% – but the good news is that balsam does not have a persistent seed bank.  Seeds only survive in the soil for around 18 months.  This means two to three years of control work at a site can be all that is required for successful balsam removal – as long as new seeds are not being brought into the site to replenish stocks!

A note on Japanese knotweed

Japanese knotweed (one of our target species in the project) is not of concern when it comes to seeding – it spreads solely by root and stem fragments.  While it does produce tiny white flowers each year it doesn’t set seed.  In Britain Japanese knotweed plants are all female with male sterile flowers. Its vigorous powers of vegetative reproduction mean that it has been able to spread to all parts of the British Isles without the aid of sexual reproduction – therefore it is classed as a single, exceptionally widespread clone.

Stopping the Spread

Everyone can help in stopping the spread of giant hogweed and Himalayan balsam seeds by practising good biosecurity – checking boots, equipment and vehicles for seeds and carrying out regular cleaning of these items between visits to different countryside sites.  You can find more information on good biosecurity practice on our website.

Autumn is the season

Of course, although we’ve covered giant hogweed and Himalayan balsam specifically here as problem and target species of the Scottish Invasive Species Initiative, do remember that not all plants are invasive.  Autumn is the main season for the setting and dispersal of seed of the majority of plants in Britain so now is a great time to see plant reproduction in action. 

As you’re out and about in the coming weeks take a second to appreciate the evolutionary genius of our plants as they spread seeds by wind, water, explosion, adhesion, using hooks to attach to passing animal traffic and as part of enticing fruits and berries for animal helpers to enjoy and transport.  You’ll be amazed at how many different tactics and methods there are – tell us how many you see.  

For more information about the work of the Scottish Invasive Species Initiative please visit our website – www.invasivespecies.scot

Coronavirus, community conservation and the green recovery

Can a community and volunteer based approach to conservation projects lead the green recovery after coronavirus?

Callum Sinclair, Project Manager, Scottish Invasive Species Initiative
May 2021

As we emerge from the 2021 lockdown, we reflect on the impact the coronavirus pandemic has had on the Scottish Invasive Species Initiative.   As a project we weathered the Covid storm surprisingly well.  Although activities were constrained, we kept invasive plant species in check and maintained our mink monitoring and trapping network.  We credit this to taking a community-based approach to invasive species management – and so we pondered what we have learnt and whether other projects could take a similar approach to help deliver a ‘green recovery’ after the pandemic.

Community volunteers in Nairn.

Community control vs Covid

At the heart of the Scottish Invasive Species Initiative are the local people who care for their local environment.  An initial and ongoing programme of awareness raising and education activities raised the profile of invasive species and their impacts. This generated significant buy in and enthusiasm to get involved from land managers, local groups and organisations, businesses, and individual volunteers.  Having recruited and enthused, we support and enable people to actively volunteer by providing training and helping them gain qualifications and experience.  This network of committed people is gaining the skills needed to make a difference to their local places – in this instance controlling invasive non-native species – both now and in the future.

When the spring 2020 lockdown occurred we weren’t, like everyone else, able to carry on as usual. It was unclear if we were about to lose a year and give up the gains made by the project since 2018.  Rather than regress, however, what we witnessed instead were the investments in embedding skills and training with local communities paying back. Farmers and land managers used their staff (trained by us) to carry on giant hogweed treatment when we couldn’t, and local people headed out to pull Himalayan balsam at sites we’d worked on together previously.  Mink raft monitoring volunteers used their daily exercise to visit and check their rafts – telling us that this small activity gave them a purpose and made them feel they were making a difference during an immensely difficult time.  The project didn’t grind to a halt – far from it – in fact we perhaps were able to snatch a glimpse of what might happen when the Scottish Invasive Species Initiative is no more.

We believe that this approach – investing in communities, training volunteers and engaging people locally can provide effective and sustainable benefits – as endorsed by the enthusiasm of our volunteers and partners to carry on invasive species control when we weren’t around. 

To date volunteers have contributed a total of 2,181 days to control invasive plants and 119 volunteers have been put through their pesticide application course.

Building community resilience

Taking a community and volunteer-based approach – rather than just employing contractors on an ongoing basis – also provides benefits to the people involved.  Volunteering, pretty much any volunteering, is much more than just the activity itself.  In our case people are making a real contribution to their local environment. But the benefits are much wider than that. Being involved within their community, meeting other people and socialising, being physically active and engaging with nature – these all contribute to improved physical and mental wellbeing.  We believe these benefits have helped give people greater personal resilience to the individual and collective stresses we have all felt during the coronavirus pandemic.

Our engagement work in communities is wide and varied.  It ranges from providing education resources for remote use and our direct education work in schools, to partnerships with farmers and universities to find alternative and innovative techniques for invasive species control.  Engaging and enabling land managers to be a central part in the  development of potentially more sustainable and affordable invasive control methods – such as sheep grazing to control giant hogweed – helps these businesses to see alternative control strategies and be more resilient to future change.

Our Macduff sheep grazing trial in partnership with a local farmer is investigating if and how managed sheep grazing can be used as a form of chemical-free, low intensity giant hogweed control.

Environmental benefits

This community-based approach, as well as empowering people, also has environmental benefits. 

Invasive non-native species require long term management and commitment.  They often produce large numbers of seeds or have persistent rhizomes and require treatment year on year. The American mink needs ongoing control to continue to depress population numbers and counter inward migration. These animals travel great distances to secure new breeding territories and can quickly repopulate previously managed areas. Having an upskilled, enthusiastic and committed local community group willing to, for example, ‘adopt’ a section of river to deliver annual plant control and/or mink control can be effective through their collective efforts – both  providing sustainable and economically effective approaches to management.

Thanks to the monitoring and trapping work of 360 volunteers maintaining 670 rafts and traps, 388 mink have been removed. This provides benefits to the local native wildlife populations, particularly water voles and ground nesting birds.

Reaping the rewards

Restored river habitats and, in turn, landscapes that are free from invasive species give so much back to us.  Our rivers are important for recreation and provide brilliant opportunities to exercise and have fun or places for quiet reflection to boost mental wellbeing.  The connection between people and nature – widely recognised as providing significant health benefits – is further enhanced when people have directly contributed to the care and conservation of the environment.

The importance of connecting with nature has been widely recognised throughout the pandemic.  Many of us discovered, or rediscovered, our local green spaces and enjoyed, and needed, the serenity these places and being outdoors brought.  

As we carefully step into what, we hope, will be our recovery from the pandemic, we have the opportunity as a society to reshape and rethink the way we do things.   We can find new and sustainable ways to work which provide long-term benefits both to people and the environment – the “green recovery”.  For us at the Scottish Invasive Species Initiative we’re not sure that is actually such a new thing – it’s the ethos by which we’ve worked since we started.

Our rivers are important places for recreation and reflection.

Is the model sustainable?

The approach we take – working locally with partners, communities and individuals – undoubtedly benefits both people and the environment and fosters strong connections between the two. 

Volunteer input to the project – 9,794 volunteer days contributed, equal to 46 full time equivalent staff from March 2018 to March 2021 – is incredible and encouraging.  The work completed through these contributions, given by 650 people, would simply not be affordable to the project otherwise.  Each and every contribution – large or small – is important to us but, perhaps more significantly, important to the person donating their time.

The Scottish Invasive Species Initiative continues to build this community network so the work we have started can be a self-sustaining after we have gone.  The work continued by our volunteers and community network during the 2020 coronavirus lockdown suggests this can be the case. But we recognise that to sustain, connect and coordinate a volunteer network to a common and shared purpose will need support and resources.  Maintaining enthusiasm, preventing ‘volunteer fatigue’, continually recruiting and supporting volunteers, training and providing local co-ordination are all essential to the success of this approach. However, the scale of return we find would suggest these investments are both extremely cost effective and environmentally beneficial.

The scale of achievement in 2020, despite working restrictions due to the pandemic.

So, while the coronavirus pandemic has reached every part of our society and touched so many of us personally, we believe there are lessons from the period that can help us in the future.  Investing in people and communities is always worth it to build support, capacity and commitment.  When investments are maintained the benefits continue.  If those investments cease, then the goodwill and benefits generated from all that has gone before are lost. 

As a project we have emerged relatively unscathed from the coronavirus lockdown – we know many have not been so fortunate. We believe the community-based approach we have adopted and the hard work and dedication of our many, many volunteers have been central to this.  We simply can’t thank these people enough.

To find out more about our work and how to get involved visit our website, follow us on social media or contact us on sisi@nature.scot

Stopping mink in their tracks – tips and tricks of the trade

Karen Muller, Project Officer, Scottish Invasive Species Initiative.
May 2021

Sleek, dark brown fur, flashes of white under the chin and a bounding gate or streamlined-shape cutting through water – the invasive non-native American mink. In the last 50 years they have become a more common sight along our Scottish watercourses and coastlines than we – and our native wildlife – would like. 

The devastating impacts of this adaptable and ferocious predator are clearly apparent – mink predation contributing to significant declines of native wildlife species, particularly water voles and ground nesting birds.

Over the last 15 years much mink control has taken place in Scotland.  However as these are wily creatures who think nothing of travelling 80km to find new breeding territories and craftily avoid entering traps their removal is not straightforward.  So, here are some tips and hints from the Scottish Invasive Species Initiative for successful mink trapping and how to out-trick these irreverent tricksters.

Please note – this article is not a guide to trapping.  Trapping should only be undertaken by trained people who understand their responsibilities regarding animal welfare, humane dispatch and relevant legislation.

American mink (photo credit – Liam Skinner)

Understand your foe

Mink are very adept semi-aquatic predators, active during the day and night and feeding opportunistically on a wide range of prey, such as fish, amphibians, birds (and their eggs), rabbits and other small mammals.

They are solitary and territorial animals – a female territory will cover around 1-3kms while male territories are usually larger (5kms) and can span across several female territories.  It’s worth noting that territories in good quality habitats will be quickly recolonised if the original occupant has died or been removed.

A good territory will be close to freshwater and often along a river in low altitude farmland, marshland or woodland edge with a plentiful supply of food e.g. rabbits.  Coastal areas are also popular – but mink still need a freshwater source nearby to clean their coats regularly.

To trap or not to trap – that is the question

As traps must be checked every 24hrs trapping can be time consuming, so it is worth monitoring for mink presence first and only starting trapping when you know mink are in the neighbourhood.

Mink monitoring is done by using a floating raft with a clay pad – to record footprints.  The raft is easily switched to trapping mode by adding a live capture trap when you know mink are present.  Read more about mink monitoring rafts on our website.

The mink monitoring raft – the clay pad sits inside the tunnel.

It’s also worth remembering to keep in touch with neighbouring monitoring rafts – our mink control is part of a large scale effort and so if you find mink signs let your neighbours know so trapping effort can be co-ordinated. The chances are that, due to their transient nature the mink you detected might have already carried on upstream and already be in your neighbour’s patch!

Alternatively, you can use a trail camera, or look for field signs if you don’t have a monitoring raft.   Check muddy or sandy banks for tell-tale footprints, bridge arches or prominent rocks for scat and look for flattened trails on riverbanks. 

Key trapping times

The best times for catching mink are pre- and post- breeding periods when mink are mobile and so there is a greater likelihood of catching them. Trapping success at these times will have a greater impact on the overall mink population.

Between January and March, many mink are transient and travel widely outside of their territories – males searching for a mate and young females searching for a breeding territory. Catching mink at this time will avoid successful breeding and prevent new mink being added into the population mix.

In summer family groups emerge from the den and by early autumn young mink are starting to leave their natal home territory but still congregate quite locally. These juvenile mink are extremely inquisitive and naïve making them easier to catch – so from July – October is the second critical trapping time.

Young female mink caught in trap.

The ‘how’

There are many native and domestic animals which can frequent the same habitats as mink – so we use live-capture traps and release non-target species unharmed.  Placing the trap on a floating raft on water further reduces the likelihood of catching non-target species as many of these are less likely to make the swim to the raft and trap.

Always cover your trap with a wooden tunnel for shelter and securely tie both the trap and tunnel to the raft.  This prevents the trap being dislodged by an angry mink or another animal and avoids the risk of accidental drowning.  Raft and traps units should be disabled or removed if the river is going to be in flood.

Live capture trap set on a mink raft, under the tunnel.

Location, location, location

Finding the right spot in the river for your mink raft and trap is the number one deciding factor in capture success – so here’s some handy hints to help you site your kit effectively on the water:

  • Look for confluences, where two water bodies join – you are doubling your chances that a mink will come across the trap by following either of the rivers or burns.
  • Find freshwater sources along coastlines – sooner or later mink are bound to search them out and use them.
  • Use pinch points – where mink are naturally forced through smaller gaps – as mink traffic can be funnelled towards your trap.  These can be:
    • under/near bridges or on bridge foundations/arches
    • culverts
    • weirs
    • in-stream islands
    • inflows and outflows on lochs
  • Select a sheltered spot out of the main flow – mink are good swimmers but they are not daft and will use the most efficient route to pass through their territories. Slow glides and slack water which make for easier swimming are ideal.

Remember – the location is no good if you can’t safely reach it in both high and low flow conditions – double check this first.  Also ensure if placed near a structure like a bridge or culvert that your raft will not cause a blockage in a flood.

A perfect spot at the confluence of two water courses.

A raft set up won’t be suitable for all locations – sometimes you can set a ground trap.

In these cases, you need to think like a mink!  Consider the likely routes mink use to move around.  In coastal areas, on beaches, this could be along the bottom of cliffs or harbour walls or between rock outcrops or prominent rocks.  Inland look for trails through vegetation along the bank, along hedges or fence lines, or fallen logs and wood and rock piles – even better if you find a well-situated log or rock pile and can fit the trap amongst them.  A mink might go for a rummage there for their next meal.

Note – If using a ground trap ensure the location is not at risk of flooding or within the tidal area. If in doubt put your trap on a raft, tied with enough slack that the raft can move in the case of water levels rising unexpectedly.

Please keep in mind that, any spot, even if it ticks all the boxes above is likely to be of little use if it is in too public a place.  We have had equipment vandalised or removed in the past and, given that if you catch a mink it will need to be despatched this task is not one which should have an audience and you certainly do not want a member of the public approaching a trapped animal.  If in doubt – find another place.

Ground traps; under a rock (L) and in a well camouflaged tunnel (R)

So, you’ve found your spot; you’ve set up your trap – time to open the box of tricks! Read on.

Trapping Hacks

Mink are curious, and you may never need to reach deep into your bag of tricks.  But if after a few weeks you are not having success then it may be time to try something a little different.

Location and set up:

  • Move your raft slightly -Try swapping to the opposite bank or a move upstream or downstream by 200 metres. Mink are fickle and these moves can often make a difference!
  • Change the direction of the trap opening – Footprints on your clay pad may give a clue to the general direction of mink travel so switch things around to see if that helps.
  • Try a double ended trap – Set two rafts with two traps opening in opposite directions. Or if on land set two traps up back to back.
  • Use camouflage – Your mink might be shy, so blend the unit into the environment. Pile some vegetation on top of a floating raft and tunnel and weigh it down with rocks.  If on land, cover it with small logs, branches, or rocks.
  • Make it obvious – This is a bid of a reverse to the camouflage suggestion above but, in non-public areas, you could also play to the mink’s curiosity and have the raft/trap in plain sight.  Sometimes the animal can’t resist the urge to explore the new addition to its habitat.
  • Make the tunnel appealing – Stuff some dry grass or other vegetation between the trap and tunnel – it creates an appealing tunnel to explore and a trapped animal to make a cosy nest from material pulled through the cage.  Make sure vegetation won’t be a hindrance when it comes to animal dispatch.  There is an added bonus here – if you catch a mink this vegetation will be saturated with scent and might entice the next one to the trap too!
  • Make sure it’s stable – If trapping on land, make sure your trap is stable – use stones or wood if needed. A wobbly trap can dissuade a mink from entering it or worse, set the trap off when knocked from the outside.

Go mad with camouflage (L) or line the tunnel with dried grass (R)

Baiting is usually unnecessary but if you do feel you need a little bit of extra help, you can try baiting with food, visual attractants or scent:

  • Food – Stab a cat food pouch a few times and hang it in the back of the trap or season your raft with a bit of oil from a tin of sardines or something else debatably “delicious” smelling. Don’t use actual food – you’ll attract every animal in the neighbourhood!
  • Visual attractants – Hang a bit of tin foil or a budgie mirror in your trap to grab the mink’s attention – get creative!
  • Scent – A scent lure holds the biggest potential, because mustelids use scent marking to communicate with each other. So, use of scent can be effective in enticing territorial animals to investigate a trap more closely – even the wily ones that turn their noses up at anything else.  There are options of how to do this but whatever you do – wear gloves!

You can collect your own scent – though this often isn’t for the faint hearted.  You can –

  • Relocate scent doused vegetation, tunnels, or traps after a mink dispatch to a different raft – though that may be impractical on a day to day basis.
  • Harvest your own scent – This is perhaps not for the squeamish or faint nosed – but I have experimented with scent harvesting from dispatched mink. A biodegradable cigarette filter, held in forceps, is saturated with “Eau de mink” from their anal scent gland. This can be done by just bringing the filter contact with their anus or, if we take it a step further to harvest even more scent, can be brought into contact with a scent gland after it has been extracted from the mink.  Not for everyone this!

Wire is threaded through the filter which is then hung from the cage grid above the trap treadle to entice the mink to enter as it takes a closer sniff.  These “scent bombs” can be stored in sealed plastic bags and added to traps as needed. This method has been used in other mink eradication programmes in preference to baiting with food.  An advantage of scent is it is more likely to specifically attract mink compared to food aromas which may also attract non-target species such as rats, otters or the odd adventurous cat.

Finally, a tip that makes your life easier – especially if your trap is located on a small island, or in a difficult to reach areas.   Attach a flag to your trap door as a visual aid to check on the status of your trap – some trap designs are better suited to this than others, and some are not suited at all but it can be really helpful. When the trap door is open the flag is up, when the trap door closes the flag goes down and is no longer visible – time to check on the trap!  You may even be able to check on your flag with binoculars from a distance. Watch a video of Karen demonstrating the signal flag.

All of the above should give a good starting point.   But of course, sometimes you may still catch nothing – remember you are pursuing a wild animal which won’t always behave as we hope or expect it to.  Be flexible and try something new now and again.

A bit of patience and luck results in a capture.

Sometimes, of course, it’s not you or the trap itself.  Perhaps the mink was transient (just moving through) and won’t come back, maybe it found itself in a different trap in the area or met its demise in a natural way, or possibly there is too much disturbance at your location and the mink doesn’t take time to investigate.  Or maybe you have a wily and cautious animal which simply won’t enter the trap pretty much whatever you do!

Despite our best efforts, there is always a little bit of luck and patience involved in mink trapping. Remember no signs of mink is a good sign – but please remain vigilant so we are ready when an animal heads your way, don’t get disheartened and don’t give up.  And while you’re there,  remember to take a moment to enjoy the native plants and animals living and thriving around you, breathe some fresh air, listen to the birds and relish the opportunity to get to know parts of your local river better you’ve never explored before.  Nature is good for you!

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Read more about the Scottish Invasive Species Initiative Mink Control Project on our website (www.invasivespecies.scot). Most of our rafts and traps are looked after by volunteers, if you’d like to find out more about getting involved read more about volunteering or contact us on sisi@nature.scot

Please note – our mink project only operates in Northern Scotland – specifically Highland/Eastern Perthshire, Angus, Aberdeenshire, Moray, Inverness-shire, Ross-shire and West Sutherland.

A day in the life of a SISI Project Officer

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

James

We asked our very own James Symonds, what a typical day of a Scottish Invasive Species Initiative (SISI) Project Officer looks like.

As a Project Officer, I am responsible for the management and co-ordination of invasive species control across four rivers in Moray and Speyside; the Rivers Spey, Findhorn, Nairn and Lossie.  Our main species of concern are; American mink, Giant hogweed, Japanese knotweed and Himalayan balsam – although we also have an interest in White butterbur and American skunk cabbage.

But what does a day in the ‘office’ look like for a SISI Project Officer?

Well that changed significantly this year with the coronavirus pandemic, but following lockdown we managed to get back out in the field to continue our work – albeit with changes to our work practices to keep everyone safe and whilst balancing home working and home schooling challenges.

My typical workday starts the same as any other for a father of 2 small humans – unsocially early! After making my way to the coffee pot and feeding the rabble I can check my work phone. I am checking my “Mink Police” app for any mink traps activated overnight and to see if any volunteers have been in touch about their mink monitoring rafts or traps.  All clear!

The Mink Police units are great innovations. Live capture traps, by law, have to be checked at least once in a 24hr period to meet animal welfare protection requirements.  The Mink Police units, using a combination of technology and magic, send multiple daily updates for specific trap locations which negates the need to physically check each trap in person each day. They allow me to remotely check the traps wherever I have access to Wi-Fi or mobile signal and, most importantly, notify me instantly if an animal has been caught.  This means that traps can be deployed to areas where, for example, mink have been sighted in physically difficult access locations or where we don’t have an elusive local ‘trapping volunteer’ to do these daily checks.  Using Mink Police units I can monitor multiple traps across a wide geographical area myself.

Mink Police unit mounted on top of a live capture trap

After finally managing to get a shower and get breakfast, I double check the weather for todays planned activity – Giant hogweed spraying. The weather looks good so I drop a text to all of the volunteers who have offered their help to reconfirm the meeting time and place.

I visit the stores and pick up all equipment required for the day and make sure I stock up on the ever-essential tea and biscuits on the way to site.

After a quick meet and greet with today’s volunteers, I go through the essential risk assessment and tools talk.  Much of the time we work on uneven terrain alongside rivers and today we are working with Giant hogweed – a dangerous plant with photo-toxic sap.  We also have in place additional COVID-19 working adaptations which need to be explained.  Safety and volunteer welfare is our number one priority.

Volunteer spraying Giant hogweed

We kit ourselves out with protective clothing, fill our knapsacks and set to work.  Today we are spraying in about six acres of riparian woodland with frequent sizeable Giant hogweed stands.  One of my volunteers is new, so I work alongside them offering support and supervision.  Pre-coronavirus there would be a team of volunteers working with me – battle hardened and dedicated hogweed assassins who gained their pesticide application qualifications with us – but today it’s just three people to keep numbers low and allow for social distancing.  We work in a rough line moving in a zig-zag upstream hoping to catch all of the hogweed we see on the way.

We started at 10.00 am it’s now 12.30 pm – definitely time for a proper break.  We put our knapsacks down and set up camp on the riverbank.  On a normal volunteering day I would  pull out the Kelly kettle, tea and biscuits – chocolate hobnobs if they are lucky – offer a demonstration on how to light the kettle using a fire steel and natural tinder and the volunteers would have a go at fire lighting themselves.  This year we’ve had to ask volunteers to bring their own flasks which is a shame as we like to offer additional activities alongside the hard work of plant spraying.  We appreciate the time our volunteers give to us and want to keep each day varied and fun for them – that way they might come back again!  

Putting the kettle on!

I check my phone and whilst we were working a trapping volunteer has called – she has a mink in a trap on another river. I phone back and she confirms the trap was empty last night but a mink has been caught this morning.  I’ll visit as soon as I am finished on site.

We spray for another 70 minutes and manage to cover the whole woodland.  My volunteers (and myself) have worked hard today but it’s been good fun.  As a reward I let them all go home early, 2.45pm instead of 3pm!  I’m nothing if not generous….

After the plant control equipment is cleaned down and packed in the car I can make my way to the mink in the trap. It’s a large mink and I have the unhappy task of humanely dispatching the animal.  This is done quickly, quietly and discretely with a high-powered air pistol. I take some basic measurements and sex the animal – a male.  You can tell this by feeling for a small bone between the hind legs – the baculum – present only in males. You can work out what this identifying feature is I’m sure!

Non-native American mink caught in trap

Dispatching mink is not something I or the project enjoy – but it is essential.  The mink is a voracious predator and their presence has a devastating impact on native wildlife.  For example, since the introduction of mink, Water vole numbers have declined by over 94% across the UK – largely due to predation.  They also have a negative impact on populations of native ground nesting birds, amphibians and fish species as well as taking domestic fowl.

I get home, change a nappy, check my emails and follow up with volunteers planning on coming out tomorrow.  The weather is looking wet so instead of spraying Giant hogweed we will decapitate the flower heads using pole saws – always fun!  I am just about to email a few volunteers about later in the week when my 4-year old runs in and rugby tackles me – it’s time to finish work for today.

Using a pole say to remove flower heads from Giant hogweed

Invasive species control work is seasonal so once we are done with Giant hogweed, we move on to pulling or slashing Himalayan balsam – great for all the family to get involved in and then, as autumn looms on the horizon, we move on to spraying or stem injecting Japanese knotweed.

The specific threats these plants pose vary in one way or another but what they all share is the fact that they are so successful in our climate and our native flora cannot compete. If left unchecked we face a massive loss to biodiversity, destabilisation of our riverbanks and very different ecosystems to the native ones that should be present. 

Injecting herbicide directly into Japanese knotweed stems (L) and slashing Himalayan balsam (R)

It’s been a productive day and there is a tremendous sense of achievement seeing what a huge difference can be made in such a short space of time with so few people.  I have missed the larger volunteering groups this year, it’s always good to get a big crowd out, but we soldier on for now and hope to get everyone back together next season.  The volunteering opportunities we have been able to offer this year have never felt so important – as well as helping nature they provide valuable time outdoors and social opportunities just when we’ve all needed these the most.

Volunteer groups 2019

If you’d like to find out more about getting involved and volunteering with James and the Scottish Invasive Species Initiative read more on our website.

Adventures with Bonnie – training a mink detection dog

Mirella Toth, Project Officer, Scottish Invasive Species Initiative
October 2020

I started to volunteer for the Scottish Invasive Species Initiative in March 2019 and have loved being involved ever since. I am from Hungary, am a motivated practical conservationist and love being outdoors and feeling like I’m doing something that matters.  I learnt a lot being a volunteer and I was so pleased that I had the opportunity to join the Scottish Invasive Species Initiative team this summer as a Seasonal Project Officer and learn even more.  As well as controlling invasive plants, part of my job was to work on the American mink control project, finding and catching invasive mink in the Spey and Findhorn, Nairn and Lossie catchments.  As well as conservation I have another passion – dog handling and training which I was able to use this summer.

Bonnie, a Hungarian wirehaired Vizsla

I used to train dogs for hunting as well as having over 7 years’ experience training police and truffle dogs in Hungary.  When my boyfriend took a detection dog handler job with the Orkney Stoat Project, it opened my eyes to the possible use of dogs to help find American mink in the field.  Imagine how amazing it would be to walk along the riverbanks, have a dog indicate the presence of mink and so know where to place our traps.  I thought this could be my own project within the Scottish Invasive Species Initiative and so, when I had the opportunity to get a puppy my journey with Bonnie started.  

Bonnie at 3 months old

Bonnie is a Hungarian wirehaired Vizsla. I have previous experience with the breed – they are excellent hunting dogs and good trackers which are ideal characteristics for my planned mink detection role. She is now 1 year old and is amazing.  I started her obedience training when she was around 3 months old and moved on to search work a little later.  Because of her young age she can still be easily distracted – a butterfly fluttering by or even her own shadow are sometimes more interesting distractions which makes the training more fun from my point of view.  It is always a pleasure being around Vizsla’s – they are so charismatic.

I started her search training when she was 6 months old. Whenever I am working with her I put a harness on to show her that she is working – if she has a harness then we are working if not then the walks just for fun!   My priority was to get her to confidently detect any sign of mink in the field.  I started her training in my garden with a dead mink – which she was really interested in – and then later moving out and progressing to the banks of the River Spey where we could look to find some real-life mink tracks and signs.

Bonnie in training

Bonnie took to the job really well and during the summer she was a huge help to me when on the trail of the mink.  When our volunteers on the River Spey found mink signs on their monitoring rafts it was up to me to put out traps in the area to try and remove the culprit. Initially (pre-Bonnie!) I spent hours looking for mink tracks and signs on the ground and, using my experience and knowledge, set my trap in a suitable place. I then waited and checked the trap each day but didn’t catch anything – the mink can be an elusive quarry. Towards the end of the summer I felt Bonnie was ready for her first real mink mission on the River Spey.  I took her to the river and she soon indicated on a spot on the riverbank – so I moved the trap there.  The result? Success – I caught not just one, but to date, four mink from Bonnie’s trap!

Success! – a mink caught in Bonnie’s trap on the River Spey

But her success on the Spey was not just luck. On the River Nairn I had the same situation.  Volunteers reported mink sightings and although I had my traps out and set after weeks and weeks, nothing had been caught. We decided a change of plan was needed and that we should move the traps to a new location and so I put Bonnie in the car and we headed to the river. Again, she found a minky spot and I moved the trap there based on her advice!  A couple of days later we had caught a mink in it.

Mirella and Bonnie – in the car on the way to the River Nairn

I am very happy with the results from this summer and with Bonnie’s progress. There are so many factors to think about when locating a trap to try and increase the likelihood of catching the mink and, even for the experienced, there is still a good bit of luck required!  I think that even an experienced trapper would save so much time and effort with the help of a trained dog like mine.  Although I’m moving to a new job for the winter, I’m sure Bonnie will come back and find more American mink for the project in the future.  Watch this space!

Bonnie checking a trap is placed to her satisfaction!

If you’d like to find out more about the Mink Control Project or are interesting in volunteering and monitoring a mink raft or trap visit – www.invasivespecies.scot or contact us on sisi@nature.scot

The ins and sprouts of Giant hogweed control

Karen Muller, SISI Project Officer
June 2020

If you have ever come face to stem with a Giant hogweed plant or witnessed a dense infestation, you know it to be a truly impressive plant.  Not purely because of its size – but because it makes the very most of itself in everything it does to ensure success.  Huge leaves on a tall stem shading out other vegetation, an average of 20-50,000 seeds per plant which are viable for about 3 years (some studies say up to 7 years!), a taproot that stores energy and seeds that can float in water for up to 3 days on their voyage downstream to new realms.  Easy come, easy grow.

Giant hogweed in flower

It can be overwhelming to think about how best to tackle this towering hazard, but plant yourself here for a while and let’s talk about Giant hogweed control: methods, tried and tested by us, and the (mostly) weird and wonderful approaches that the internet spat out.

Before we dive in, safety first!  Giant hogweed sap contains furanocoumarins, which enhance the sensitivity of skin to Ultra Violet (UV) light. Simply put, when the sap comes in contact with skin it reacts with direct sunlight causing photodermatitis (skin burns) and you’re often left with long-term sunlight sensitivity in that area.  So, the first step is to get suited and booted and gloved to protect yourself.  A face shield or safety glasses are also advised where there is risk of getting splattered with sap e.g. when digging or cutting the plant.

The second basic rule when tackling Giant hogweed is that you need to have a plan.  Always start from the uppermost hogweed infestation along a water course, so that when you clear an area you don’t have to worry about any more seeds floating down and re-infesting your treated area.

Safety first; get suited, booted and gloved

Green and gone

At any point, while the plant is green and actively growing, a systemic herbicide with aquatic approval e.g. Glyphosate is perhaps the most straight forward answer for dealing with hogweed near water.  Note that you require the relevant training and qualifications before you can use pesticides, particularly near water.

Using a knapsack sprayer to apply the herbicide is the most efficient option for dense infestations and extensive populations.  For less dense areas or sites with occasional plants, you could consider wiping neat herbicide on the leaves with a weed wiper or directly injecting it into the hollow stem.  However, these methods do involve getting closer to the plant – something you should generally look to avoid.

Hogweed can be resilient and so a second ‘mop up’ visit a couple of weeks later can be warranted in the worst infected areas to catch any plants missed and to make your control effective.

Herbicide application by knapsack spraying, weed wiping and stem injecting

The taproot of the matter

Young Giant hogweed plants with their turnip-like taproot lend themselves well to digging up.  This is more labour intensive but it reduces the use of herbicide, requires only basic training and can be done by anyone.  Stick your spade through the root, cutting it approximately 15 cm below ground, then dig up the taproot and leave it above ground to dry out.

A sharpened spade is about as specialised as it gets with this method – but we have dug out plenty without sharpening, too.  It just very much depends on the ground you are working on.

Small hogweed plants can be dug out

Bud intentions

If you find that time has grown legs and the hogweed plants are forming flower buds or are already fully flowering, it is best to slash their ambitions with a long handled pruning saw.  It should be an absolute priority to treat flowering plants – every time a plant sets seed you can add another three years to your treatment plan.  Seed ‘em and weep!

Giant hogweed flowers only once after growing for 2-5 years and then only if the conditions and its energy reserves allow for it.  So, if you are only seeing hogweed leaves for several years at your site, there will be flowers coming soon.  Although the hogweed plant will die after flowering a lot of later treatment work can be avoided by removing the flowering head before it sets and disperses seed.

Giant hogweed bud and flower

Long handled cutting equipment is advised – this allows you to keep a safe distance from the plant and any sap splatters as you cut it.  If cutting is the only form of control you are doing be ready to revisit the site regularly during the growing season to cut any new emerging flower spikes on the lower stem or regrowth at the crown.  Cut under the flower head first – removing it intact – then cut the stem in sections until you’re as close to the ground as possible.  If you can combine this with chemical control – treating the cut stem with herbicide – you’ll get better results.  Chemical application needs to occur relatively quickly after cutting to ensure the plant will take up the pesticide and transport it into the taproot before drying out.

Catch them early enough – while there is only a bud or white flower – and it appears safe to leave the flower head on site to degrade.  However, if the flower head has turned green the seeds might still ripen on the cut head and be viable when they drop off.  If the flower head is green, and if you can reach, carefully put a cotton bag or similar over the flower head and tie it off before cutting – then collect and burn.

Cutting flowering heads followed by herbicide application directly into cut stem

All dressed up and nowhere to grow

Suppressing new Giant hogweed growth by covering with mulch or membrane is an interesting method that does come up frequently when looking for hogweed control solutions – but we haven’t used in in the project due to the often large areas we work in.  It is most suitable for smaller areas, like a garden, and is likely to work best on areas where there are only seedlings coming through.  The idea is to cover the area with sturdy black plastic and or a generous layer of mulch and suppress seedling growth by blocking out light – a reasonably standard approach to weed suppression in gardening.  You do need to check back regularly to make sure nothing pokes through the covering.  Let us know how you get on if you give this a try.

Giant hogweed seedlings and field ploughing (image – Stanze)

In suitable locations, particularly in fields, ploughing can be a good solution.  It is most effective if combined with chemical or mechanical control – cutting the plant low to the ground first, or treating it with herbicide and waiting for it to take effect, followed by deep ploughing the area.  After that most seeds, or seedlings, will be far enough underground to not see the light of day again.  If, after initial treatment, more mature plants are being ploughed the large taproots should be removed as much as possible to prevent regrowth.  Like the covering, we haven’t tried this approach ourselves, but in the right location this could be well worth a whack.

Rooting for native species

Where possible, and particularly in areas of previous heavy infestation and a built-up seed bank, reseeding with native plants and trees can make control efforts more effective.  The aim is for native vegetation to outcompete new hogweed seedlings which emerge from treated areas – this sort of planting can also help stabilise bare riverbanks following treatment or winter die back.  Timing is everything here – long-established, dense hogweed infestations cannot be defeated by reseeding alone.  Manual or chemical control is necessary until mostly just new hogweed seedlings are appearing and their density is reduced to a degree that they will not easily overpower the native species you have seeded.

Flocking to the rescue

Situation permitting, grazing can be an effective approach in Giant hogweed control.  Sheep, goats and cattle will readily eat hogweed and pigs even go one step further by uprooting and feeding on the taproot as well.  However, there are a few things to consider before sending the four-legged cavalry into the field.

Woolly warriors brought in to battle Giant hogweed

Hogweed infestations in fields, woodlands, or at the very least a few meters removed from the riverbank, can be suitable locations for grazing control.  However, stock still need to be managed and so the costs of additional fencing, gates etc should be considered.

Hairy breeds of animals, with dark skin, are the best choice to prevent the sap having negative effects on them.  Black face sheep, for example, have successfully and without injury been used to graze hogweed. Since 2014, such a trial has been taking place in the Deveron catchment, with a second grazing trial site set up in 2019 by the Scottish Invasive Species Initiative (read about it here).

Livestock prefer to graze younger or smaller plants, so grazing should start early in the growing year as hogweed emerges.  The grazing of seedlings can be very effective due to the lack of energy stored in the taproot at that point in the plants multi-year life cycle.  On the other hand, grazing of more mature plants might not be to every animal’s taste – although we have witnessed sheep taking down flowering plants during our trials – and while it prevents plants from growing larger, grazing doesn’t kill mature hogweed as the already stored energy in the tap root allows the plant to make a come-back that same year or the following year.  In this instance, the grazers merely work from season to season to prevent regrowth and progressively deplete the energy store – preventing flowering and spread.

Like chemical or mechanical control grazing is required at a site for a number of years before you can call it a job well done and consider the plant eradicated.  Ongoing review and assessment of livestock density and grazing days is also important to prevent overgrazing of other vegetation – otherwise you might just be replacing hogweed and grasses with native recolonising species such as nettles and dock.

The sheep in the trial developed a taste for Giant hogweed and made short work of these plants

A word of caution

Household ammonia, salt, liquid nitrogen and heating oil, amongst other things, are at times suggested on the internet for use as alternative approaches to Giant hogweed control.  We haven’t tried any of these methods ourselves and neither have we found any robust evidence to suggest that any of these would be effective.  The potential negative impacts on soils, waterways and wildlife when other proven methods are available means we won’t be exploring these methods further.

Summing up

Tackling Giant hogweed isn’t for the faint-hearted and isn’t for everyone.  Wearing protective gear is essential and specialised training is required to use pesticides safely.  But, hopefully, there are control methods, such as cutting flower heads, digging of roots, mulching or use of barriers in your garden or grazing with animals in larger spaces that might work for you in your own hogweed situation and circumstances.  So, don’t be afraid to try this at home – but do be careful and do some thinking beforehand.   If you do decide to take hogweed on use a method that is suitable for you and your site, only proceed after proper planning and, if needed, training and absolutely always with the correct protective clothing!

Just remember, always check and clean yourself and your equipment before leaving a site to avoid further accidental spread, prioritise control strategically in a downstream direction and focus on plants about to flower.

If you are in the Scottish Invasive Species Initiative area and want to help our control work then get in touch (E: sisi@nature.scot) and we will see what opportunities are available in your patch. Read more on our website.

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…

Deploying a natural enemy for one of the UK’s most invasive weeds

Wayne Coles, CABI
Jan 2020

For 180 years Britain’s waterways have gradually become clogged and choked with what the Victorian gardeners thought in 1839 was a pretty addition to the nation’s landscape.

But Himalayan balsam (Impatiens glandulifera), also known as Touch-me-not Balsam and Policeman’s Helmet, is no longer regarded as a visual delight but rather a blight upon Britain’s riverbanks, streams, ponds, lakes, damp woodlands, roadways and railways.

Himalayan balsam was brought to the UK by the Victorians as an ornamental plant but it has since become the scourge of the nation’s waterways – Photo: CABI

In fact, the plant – whose native range is the foothills of the Indian and Pakistani Himalayas – is considered one of the UK’s most widespread invasive weed species competing with native plant species for space, light, nutrients and pollinators, thereby reducing local biodiversity.

Though it dies back in winter, Himalayan balsam is – amongst other places – causing a nuisance on the River Tweed in Scotland as part of a nationwide invasion which in 2003 the Environment Agency (EA) has estimated would cost £300 million to eradicate. The plant has since continued to invade new areas.

Nevertheless, science is trying to fight back against the Himalayan balsam ‘menace’ with a biological weapon in its arsenal – the fungal agent Puccinia komarovii var. glanduliferae– that will be released into Scotland in 2020.

Dead plant material from Himalayan balsam can also enter rivers and increase the risk of flooding.

It was back in 2006 when CABI was asked by the EA, the Department for Environment, Food and Rural Affairs (Defra) and the Scottish Government to find a reliable. effective and safe natural enemy to help control Himalayan balsam – a journey which has seen scientists adopt a ‘classic approach’ and return to the foothills of the Himalayas for a natural solution.

After sourcing a rust fungus from the Puccinia species and bringing it back to CABI’s quarantine facilities in Egham, Surrey, for further analysis and rigorous testing scientist now believe they have a tangible biological solution for the invasive weed which will be released with funding from Scottish Natural Heritage’s Biodiversity Challenge Fund in partnership with the Tweed Forum.

Kate Pollard, a Research Scientist at CABI, said, “The highly damaging fungus was identified by CABI in the foothills of the Himalayas, where it infects leaves and kills seedlings of the plant, helping to maintain population levels.

Extensive laboratory testing was undertaken under quarantine conditions to confirm that the fungus was highly host-specific, infecting only Himalayan balsam, and safe for release.

“Approval to release the rust into England and Wales was granted in 2014 and since then, the rust has been released at 47 sites across 19 counties. Field results are promising with high levels of infection, spread and overwintering recorded at a number of sites.”

The rust fungus Puccinia komarovii var. glanduliferae could go a long way to helping to solve the River Tweed’s Himalayan balsam invasion – photo: CABI

Prior to the ‘appliance of this natural solution, Himalayan balsam on the River Tweed has been tackled using a combination of hand-pulling the weed, thanks to an army of volunteers, and spraying.

The fungus has previously been released at a site along the River Tweed on the English side of the border. It is hoped that the release later this year will help step up the fight against Himalayan balsam on the waterway further as part of a concentrated longer-term solution.

Reference
Environment Agency. (2003). Guidance for the control of invasive weeds in or near fresh water. Environment Agency, London, UK

Find out more about CABI’s work to release biological controls to fight Himalayan balsam from the dedicated website.
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Did you know?

Himalayan balsam is Britain’s tallest annual plant with each plant tending to be around 1-2 metres high, although they can reach a height of 2.5 metres in some cases!

According to Section 14 of the Wildlife and Countryside Act 1981, it is an offense in England and Wales to allow Himalayan Balsam to spread into the wild. Therefore, it is highly recommended that you remove Himalayan Balsam from your grounds or garden.

It is important to make sure that when disposing of Himalayan balsam, the waste disposal site has a permit to accept and dispose of invasive species. As GOV.UK explains, you can be fined up to £5,000 or be sent to prison for 2 years if you do not properly dispose of Himalayan balsam and other non-native invasive plants.

The Good, the Bad and the Balsam

Karen Müller, Project Officer, Scottish Invasive Species Initiative
September 2019

Himalayan balsam season has drawn to a close. On our river banks, our staff and volunteers have downed tools for another season. The time has come for the last of the pink-petaled invaders still left standing to be pinging their seeds from ripe pods in an endless effort to increase their range. But with thousands of plants degrading in piles on the banks and tens of thousands of seeds prevented from ever reaching nurturing soil we are happy to call this a job well done, for now.

It’s time to reflect on the last few months – our highs and lows, ayes and nays, lessons learned and casting our eyes to the future.

Getting to grips with balsam

This year’s waves of heat and rain appear to have been particularly favourable for balsam, with many areas dazzling with shades of pink. To counter this, a continuous thwacking of weed whackers, scythes and strimmers against balsam stems, the sound of soil releasing roots and the popping of hollow stems under the weight of more balsam being added to piles has filled the air over the last few months. There has been a flurry of volunteer activity across the project area, making it possible that river banks from Tayside to Sutherland have decidedly less of a pink hue to them.

Volunteers come in all shapes and sizes and the one lovely thing about balsam is that its control is suitable for a wide range of ages – from primary school children to people living out their best life in retirement – and can be done in larger groups. It’s the perfect way to meet new people, partake in a hands-on activity with your kids or spend some relaxing time in nature while trying something new and helping the environment. Whether it is anglers, dog walkers, bird watchers pulling a few plants when they are out and about or individual people, schools or organisations that specifically join us project officers for a balsam bash – many a mickle makes a muckle in the battle against balsam.

Compared to other invasive plant control, balsam provides instant gratification when you look back on the area you are working on – nothing makes your chest swell with pride like knowing you have just built the highest balsam pile yet of the season. And let’s not stop there, optical illusions, balsam snowmen, a spot of friendly competition who can build the biggest pile or who can scale the finished pile the fastest and stand victoriously at its summit – the pile is your oyster.

Unquestionably, balsam control is not always all sweetness and light –the plant is willing to make use of many kinds of growing spaces and so we found ourselves thigh deep in ‘bogs of eternal stench’ or crawling around in gorse on more than one occasion. Did it stop us having fun? Of gorse not!

Through the good times and the tough, plenty of opportunities to whip out the Kelly kettle, freshly brewed tea and coffee (not the instant kind, mind!) and, most vital, chocolate biscuits, support us in keeping our volunteers in top motivation.

Time to reflect and perfect

So, what have we learned over the past two seasons through trial and error? For one, we have stocked our armoury well with strimmers, scythes, weed whackers and gloves since last year – something to counter anything the balsam might throw at us.

Selectively pulling balsam from amongst other vegetation seems to have the least impact on non-target species, if compared to mowing down stretches of bankside vegetation at more badly infested sites. But, if you’re working on borrowed time, you sometimes have to face the hard hitting questions. Mowing is effective in terms of time and effort and, thus, usually prevents a much larger proportion of seeds from dropping. So, do we mow in the hope that after a couple of seasons we have adequately reduced the density and can move on to pulling the balsam up? Or shall we pull regardless of the fact that much less can be achieved in the same amount of time? It is important to ponder these quandaries and often we have to make decisions on a case by case basis, depending on the existing vegetation, how dense the balsam has become and its potential to spread from there.

As it gets later in the season the balsam is really out to impress, growing up to two meters in height. At times the stems are growing horizontally along the ground before reaching its flowers towards the sky and roots start to form on higher leaf nodes, digging into the soil where the stem touches the ground. The trouble with this is the increasing likelihood of snapping the stalk during pulling, followed by the balsam stubbornly re-growing from the left over stem. A weed whacker can be really handy here to slash the stalk below the first node closest to the ground and curbing the balsam’s ambitions once and for all.

Casting our eyes on the future, there are always things to improve. For one, we still need to understand the distribution of balsam throughout our catchments better, so that we can control it strategically from the most upper extent moving down the river. We really appreciate reports of sightings to help us with that. The species is widespread and we know that long-term, sustainable solutions require landowners who actively take responsibility and more volunteers to support the effective removal of the plants annually. While many landowners, local communities, environmental groups and countless more are already getting involved we need to increase these efforts catchment wide moving forward.

Last but certainly not least, both this year and last year it is a must to acknowledge that every single one of our enthusiastic volunteers is absolutely wonderful and invaluable! You make it a joy to get to grips with balsam and you make the improbable possible. Not all heroes wear capes – some wear waders and gloves!

If this has inspired you to get involved with the Scottish Invasive Species Initiative or you’d like to find out more, visit our website www.invasivespecies.scot or email sisi@nature.scot