In 2023 the Scottish Invasive Species Initiative received support from Moray Council and the Ian and Claire Mattioli Fund to tackle invasive species in the Spey, Findhorn and Lossie catchments. This allowed us to trial a new method of chemical application and make rapid progress on significant giant hogweed and Japanese knotweed infestations, which would otherwise have taken several years to tackle. Find out more about these innovative methods in the blog below, written by Project Officers Karen and Elise.
Here on the rivers Findhorn, Lossie and Spey we are no strangers to large infestations of giant hogweed and Japanese knotweed, especially in lower areas of the catchments. As we work towards bringing many of our sites under control, we cannot help but cast nervous glances at the strongholds of invasive plants further downstream. Towering, dense forests of giant hogweed and tangled, impassable walls of Japanese knotweed await, daring us to even look in their direction with a knapsack. The thought of beginning to tackle these bastions for the first time is a daunting one.
But worry not dear friends, ‘tankfully’ there is a solution! In the expansive flowering fields of invasive plants, the peace and quiet was about to be broken by the sounds of ‘engine-uity’. Armed with determination, herbicide, a pressurised sprayer and, in some areas, a tractor-mounted cage, we embarked on a mission to reclaim the land for native species. Join us in this green adventure, where we turned the tide against an ocean of invasives!
Sprouting the Plan
In many places, we face expansive areas of dense interlocking Japanese knotweed and giant hogweed plants, often towering over our heads, smothering native biodiversity, and making access for effective control difficult. Traditional control methods via knapsack or stem injectors would require significant people power, time and would often mean that our control efforts would be limited to the outskirts of the densest stands, requiring a few years before we were finally able to meet in the middle.
We are left pondering how many hours will be spent bashing a path through the undergrowth with a fully laden knapsack? How many dauntless volunteers will disappear into the fray and will the biscuits we offer be enough to tempt them out again? And perhaps most importantly, how effective will our efforts be against such mature and overwhelmingly huge stands?
While there are many factors against us, there are also some crucial advantages on these sites, namely good track access, large areas of invasive non-native plants growing away from the river, and land managers who are supportive of new and innovative strategies. So, we hatched a plan that was as ambitious as it was ‘engine-ious’.
We turned to the newest weapon in our armoury; a motorised spray tank normally used by a local estate for controlling hill fires, with a capacity of 400 litres, a 50-metre hose and a lance that can spray up to 10 metres! With the tank safely loaded into our trailer and filled with the standard glyphosate and water mixture we’d use in our knapsacks (Roundup ProVantage at 2% concentration), we set off down the aforementioned access tracks to introduce the invasive plants of Moray to our formidable new weapon.
We quickly settled on a strategy and established that a team of three was optimal; with one team member staying in the trailer to keep an eye on the engine and to feed the hose out to the operators on the ground; another team member managing the hose between the trailer and the lance, ensuring it didn’t get snagged or tangled; and the last team member handling the business end and operating the lance. Working together we were able to achieve a very fine level of control with the sprayer to minimise off-target application. Using this approach our staff, volunteers, and groundskeepers were able to operate the power sprayer safely.
Rivers Lossie and Findhorn
We started the season by tackling infestations of giant hogweed on the lower Lossie and Findhorn. These areas were dominated by mature plants that were well on the way to flowering – if not flowering already. On top of that, there was also a heatwave to deal with, which would have further ‘sapped’ operators’ energy and could have proved limiting if using heavy knapsack sprayers. However, armed with the tank, we were able to travel light, with operators only carrying saws to cut their way into thickets to reach flowering heads before spraying their way out with the tank’s powerful lance. The increased range of this lance meant large areas were covered quickly and efficiently. It also meant that plants growing in areas that would be hard to access with a knapsack were given no respite as we were able to find safe vantage points and use our new-found range to sufficiently douse them with spray. Seeing the amount of ground that three or four of us were able to cover in a day was incredible – but we were hardly complaining!
Later in the year the tank had another chance to shine in the fight against previously untreated Japanese knotweed. Well-established knotweed tends to grow in large, dense stands which form thick canopies of leaves, making them ideal targets for the tank. Using the same techniques we had perfected during our days treating giant hogweed, we marched into battle against the Japanese knotweed on the Lossie. In some areas we were faced with solid walls of knotweed as well as smaller isolated clumps. To use the tank on these small sections would have been irresponsible as it would run the risk of off-target application. However, rather than just leaving these sections untreated, we instead turned to a hybrid method of treatment and tackled it the old-fashioned way, with team members working with knapsacks in tandem with the tank.
This goes to show that every site is different, and varying abundance and distribution of invasive plants require different combinations of treatment methods, as we were about to find out on the Spey.
River Spey
In the lower Spey catchment, this year’s focus with the tank was solely on untouched Japanese knotweed stands. After identifying suitable sites, we approached it in the same way as on the Findhorn and Lossie in the first instance – on foot. This was the best approach where Japanese knotweed was growing in dense but narrow stands along both sides of an estate track.
In stark contrast, the next site was 220 meters in width and featured towering knotweed wall to wall, broken only by a couple of tracks and natural breaks between the mature stands that were increasingly merging together after years of unchecked growth. We looked to elevate our approach – literally – with a tractor mounted cage to provide us with the advantage of height to spray beyond the initial wall of knotweed without having to enter it on foot. Luckily, we had a supportive land manager with a skilled groundskeeper and his tractor who came to our aid.
This came with a new level of safety considerations but armed with a helmet and fall arrester for the person manning the cage, high visibility clothing and a thorough risk briefing for everyone involved, as well as experienced operators, we took our control to new heights.
The trailer was hooked up to the tractor where the tank was manned by a team member, the hose was secured over the cab and fed into the cage where a member of staff was utilising the pressurised lance to spray as far across the top of the knotweed expanse as possible. Some of the natural breaks between Japanese knotweed stands meant that these could be tackled from a number of angles, although the centre of some of the largest expanses remained out of reach even from the cage. In just one treatment season, this approach allowed us to nearly eliminate smaller, isolated stands and greatly reduced the extent of the larger, merging areas of growth. This was particularly important in mixed sites, where the reduction of Japanese knotweed will improve the efficiency of giant hogweed control in following years.
Last but knot least
The humble knapsack will always have a place in the battle against invasive plants, but we cannot be afraid to think outside the box when faced with challenging sites. Collaboration often provides new opportunities to explore innovative control methods and bring together the different skillsets necessary to make them a reality.
The support we received from Moray Council and the Ian and Claire Mattioli Fund has made this work possible and enabled us to hire the specialized equipment required for this new method. This has allowed us to make rapid progress on really badly infested sites by covering significantly more ground, saving countless hours and ultimately being more efficient than would ever have been possible using only traditional spraying strategies. It is tricky to give exact figures as spraying on foot can be so variable, but we would estimate that using the spray tank we were able to cover 10-15 times more ground than one person could cover using a backpack sprayer in the same time period.
Having visited the sites a few weeks after treatment we are delighted with the results so far. When faced with infestations this significant the problem can often seem overwhelming, even hopeless – but take heart that there is always a solution, even on the most difficult sites!
A special thanks goes to Moray Council and the Ian and Claire Mattioli Fund for supporting the funding of this control work. Thank you also to Kellas Estate for access to the spray tank, Gordon Castle Estate for providing the tractor and their groundskeeper – and in particular for their support and confidence in us.
As always, we couldn’t have done this without our stalwart volunteers, committed partner staff and David Mitchell with his tireless skill navigating the tractor through the knotweed jungles.
The Scottish Invasive Species Initiative is a partnership project funded by The National Lottery Heritage Fund & NatureScot (2017-2023) and the Scottish Government’s Nature Restoration Fund, managed by NatureScot (2023-2026).
Scottish Invasive Species Initiative 