Giant hogweed control on the Lower Urr

Funding

The Scottish Solway INNS control and knowledge programme (Phase 1) was funded by the Nature Restoration Fund (NRF), a fund launched in 2022 encouraging projects that restore wildlife and habitats addressing biodiversity loss and climate change.

The project is now in Phase 2. Phase 2 is funded by The Heritage Lottery Fund and match funded by Killgalioch Community Funded (administered by Foundation Scotland).

The Lower Urr and Giant hogweed

The lower River Urr has a problem with Giant hogweed, a well-known invasive non-native plant species which can cause human health issues. Touching the sap can cause severe burns to the skin. The plants are extremely invasive with up to 50,000 viable seeds released from mature plants. The plants can quickly become dominant shading out and replacing native plant species. Giant hogweed spread quickly along riverbanks due to seeds being washed downstream. GFT are concerned about this, hence they are supporting landowners and stakeholders through the 'Scottish Solway INNS Control & Knowledge programme'. A project officer can provide assistance to develop and deliver coordinated and effective INNS control programmes.

GFT has created a management plan and undertaken Year 1 & 2 control on the Lower Urr which stake holders, such as landowners and volunteers, will take ownership of control to keep Giant hogweed under control in the longer term.

Introduction

An umbellifer, member of the cow parsley family which was introduced into gardens in 1820 as a curiosity and deliberately planted by rivers and ponds.  Giant hogweed (GH) is monocarpic meaning it can self fertilise, producing between 20-50,000 seeds per plant. Seeds can be washed downstream or survive more than three years in the soil making it extremely invasive.

Flower heads can be up to 80cm across and typically grow 2-3 metres in height and form dense, impenetrable stands. GH is also known for it's phototoxic sap which can cause skin burns.  Hence, GH in riparian environments blocks pathways for recreational users as well as causing a health risk. Once established GH will not only outcompete native species but will also increase the risk of bank erosion and flooding when it dies back in the winter.

The lower Urr has a problem with GH, with concerns raised by the Dalbeattie Angling Association (DAA) and members of the community regarding risk to human health and recreational access. GFT was also concerned about the negative environmental impacts linked to GH regarding loss of biodiversity and changes to the riverbank structure.

Effective management of GH involves a strategic catchment approach to control i.e. finding the upper limit of the plants and working on these source patches first then gradually moving downstream. This ensures there is no risk of re-infection for areas that have already been controlled. An effective treatment technique for GH is to treat the emerging leaves with herbicide (Glyphosate) in the spring to early summer. Caution must be taken to avoid spraying surrounding non-target plant species. Herbicide is applied using backpack sprayers by spot spraying. As the year progresses though, GH starts to flower so to prevent any seeding occurring it is advised to remove flower buds and flowering heads as well as treating with herbicide if control is left to later in the year. Flower heads are cut off using a long-handled pole saw and herbicide is sprayed to the cut stem and basal leaves. If the flowering head is starting to develop seeds, then extra care must be taken to ensure seeds do not spread. A large cotton bag or sack should be placed over the flower head and tied prior to the stem being cut. These bags containing the flower/seed head can then be burned.

 Part 1 : Landowner Permissions

GFT acquired landowner permissions to survey and control GH along a 12 km stretch of the river in 2022. Landowner permissions were obtained by going door-to-door and personally speaking to each one and maintaining contact with them throughout the survey. A map was generated from the landowner data for posterity and ease of repeating this project over the next few years.

 Part 2 : Survey

Year 1 (2022):

A thorough walk-over survey was conducted over 53 man hours (over seven days) by two members of GFT staff to map the extent of GH. Both banks were surveyed, and each GH plant was identified taking note of their size and GPS location to provide an accurate count. Where there was a large group of plants a GPS range was taken, and the number of plants noted. We surveyed a further 2km upstream of the source plants in order to be certain that was the highest point and also requested anecdotal information from landowners and the angling associations as to evidence of any plants further upstream. We also surveyed a 3km stretch of the Dalbeattie Burn to determine how far along the burn the plants had spread. The data was used to create distribution maps to help plan the control programme and as baseline data for the long-term management plan.

Year 2 (2023):

As in year 1 walk over surveys were completed by two GFT staff members over seven working days (53 man hours). Both banks were surveyed between the end of March and the beginning of April. Grid reference coordinates of each plant was recorded. Surveys in year 2 started earlier than in year 1 to ensure plants were not missed due to being hidden by other vegetation. At this point it was noted that some areas had far larger plants than others. This information was beneficial when planning and prioritising control.

Year 3 (2024)

Weather conditions in 2024 have been significantly wet, hence the PO merged surveys and control in one. The PO accompanied contractors carrying out surveys at the time of control. The first suite of surveys and control took place between the end of March to the 20th June 2024, over 21 days, and the second control took place over 10 man days, by contractors, during the middle and end of September.

Part 3 : Results

Year 1:

Approximately 1,860 GH plants were found in a 10km stretch of the lower Urr. Fifteen kilometres of river was surveyed from Breckoniehill Farm (just south of Dalbeattie) to 500m below Old Bridge of Urr on Dryburgh Farm, and also in the Dalbeattie Burn. The highest point of GH found was just above the A75 on the right bank in a stand of approximately 100 plants. This was consider to be the source of GH on the Urr with no plants for at least 2 km upstream on either bank. We are not aware of any reports of Giant hogweed further upstream in the catchment.

Year 2 :

Approximately 2,040 plants found in a 10km stretch. Year 2 control programme carried out between the 5 ^th  of May and 23 ^rd  June 2023 over seven working days with two GFT staff members. First site visits were to sections of the river with larger plants. Second site visit carried out by two members of GFT staff from below A75 (highest known point) down to Dalbeattie burn. Third site visit took place between the beginning September and end of October with approximately 250 plants found.

A targeted treatment to sections of the river were larger plants were present during surveys (downstream of Dalbeattie Bridge) first was deemed necessary to ensure that these plants were treated before they started seeding. Such approach was noted to be successful during the second site visit which started from the highest point downstream. Sections of the river which had larger plants had a second site visit at this point. A decline in plants upstream from the A75 down to Waterside Farm was noted. In year 1 approximately 143 plants were found on this stretch while in Year 2 approximately 96 plants were observed. No plants were observed on this stretch on the final site visit. Highest concentration of plants were found to be downstream from East Logan to Dalbeattie Burn. A final site visit was completed between September and October 2023 with approximately 258 late emerging plants found of which 100 plants were found at Mary’s Pool.

Year 3:

Approximately 2,000 plants were found in the 12 km stretch. A significant decline was observed at the highest known section of Giant hogweed, between the A75 and Haugh of Urr, however a large amount of plants were included in the treatment downstream at GR: 283622 559592 following landowners permissions for control being granted. A high number of plants are still present from East Logan to Dalbeattie burn.

Findings have been mapped and shared with landowners and stakeholders. Control will be taking place thereafter following the agreed management plan. We will be seeking volunteers and stakeholders to start getting involved in control work in preparation to the long-term management plan.

Part 4: Management Plan

The management plan is to spot spray Glyphosate solution onto each individual plant by accredited operators using backpack sprayers. The plants will be sprayed between April and July when they are large enough for the Glyphosate to be effective, but before the plants start flowering. If they have already started flowering, we recommend that the flowering heads be cut and placed in cotton bags for removal and then burnt. Extra care should be taken if the flowering heads have already started to seed. Once the plants have all been treated, a second site visit should occur to identify and spray any newly emerging or missed plants. Once the GH is down to a more manageable distribution and density then long term control will be passed over to landowners and stakeholders.

Part 5:

Year 1 - Management Plan

The first spraying treatment took place between the end of May and beginning of June 2022, with all GH recorded on the walk-over survey being sprayed. A second site visit took place between mid-August and late September during which newly emerged or missed plants were identified, recorded and sprayed. The effectiveness of the first spraying was assessed and recorded.

All GH recorded in the survey area in mid-May 2022 were no taller than 1 metre high and none of them were flowering.  However, on the first spot treatment completed between the end of May to the beginning of June, approximately 1,162 (62% of the population) plants had grown noticeably larger. Thus highlighting that in the absence of effective and strategic control GH will quickly grow and take over large areas of land.

Finally, the whole length was resurveyed over five working days and any GH plants controlled between mid-August and late September 2022 which showed a significant decline in numbers, with only 138 plants found, most of which were found in the tidal zone of the Urr where incoming tides compromised the efficacy of treatment. This showed that the proposed management plan has been effective in controlling GH on the lower River Urr in 2022.

Part 6:

Year 2 - Management Plan in action

As detailed in the results section, the project officer made minor adjustment to the Year 1 management plan to undertake earlier surveys and targeted treatment on sections with larger plants. This meant that sections with larger plants had three site visits. On the final visit a significant decline in numbers was observed, with only 258 plants found, most of which were found in the tidal zone of the Urr where incoming tides can compromise the efficacy of treatment.

Findings, mapped and shared with landowners and stakeholders. Control will be taking place thereafter following the agreed management plan. We will be seeking volunteers and stakeholders to start getting involved in control work in preparation to the long-term management plan.

Year 3: Management plan

The PO has made adjustments to previous years in regards to the control methodology, to maximise its effectiveness. The main aim is to treat plants before they flower to avoid increasing the seed bank. A combined survey and control visit alongside an earlier start was therefore decided upon; however due to high rainfall and water levels this was delayed, which resulted in some plants starting to flower at the time of control. The PO will aim to start control as early as possible in control season 2025.

What success of this project is expected to look like;

• As we progress through the years we are expecting a reduction in the amount of herbicide needed, fewer man hours to survey and control, less river impacted, the start of seedbank depletion; meaning a step towards the eradication of Giant hogweed from the lower River Urr.
• An on-going reduction in the seed bank annually.
• Stakeholders, landowner and the community to take ownership of control after initial treatments.
• Safer access to river banks for the local community.
• Improved biodiversity along river banks.
• Greater resilience to the impacts of climate change.
• Reduced bank erosion.