The entirety of the site is owned by a number of local landowners and the Japanese knotweed site is owned by one landowner. Within the Scottish Invasive Species Initiative, the Ugie catchment is covered by the Deveron, Bogie and Isla Rivers Charitable Trust (DBIRCT).
The upper Ugie mainstem meanders through open farmland, with thick bankside vegetation and mowed paths for angling access.
Japanese knotweed had established and formed a dense stand on a U bend of the river (NK 08092 49836) where it was outcompeting native vegetation, posing a risk to bank stability during winter dieback and presenting a source of materials to allow spread further downstream. Some bank erosion was already apparent in the bend with a large chunk of the bank broken away and forming an island in the U bend. This added to the risk of Japanese knotweed stem fragments or rhizomes breaking away from the stand and spreading downstream.
2. Background
It is not clear how or when the Japanese knotweed established at the site. There are no known stands of knotweed upstream of this site for many kilometres, with the only other known stand located in the upper reaches of the South Ugie water. Due in part to the infestation growing between the river and a fence line (so limiting disturbance), with no public access on the right bank, the knotweed had not spread extensively downstream. Only one small stand has established in the adjacent management site downstream, likely due to plant fragments or rhizomes being washed down.
The site was identified during surveys in 2018. The landowner was made aware and a treatment plan was formed for initial control work to be carried out by Scottish Invasive Species Initiative staff and a volunteer. The landowner agreed to undertake pesticide application training through the project and take on responsibility for the site going forward.
3. Management works
In 2018, treatment was undertaken for the first time by Scottish Invasive Species Initiative staff and a volunteer. Glyphosate (RoundUp ProVantage) was applied to the entire stand by foliar spray at a concentration of 20ml per litre. Annual foliar treatment was applied to any regrowth by the landowner in 2019, 2020 and 2021. Over this period there was increasingly less regrowth, with only a few stunted stems apparent in 2021. The site will be checked in 2022 and necessary follow up treatment delivered by the landowner.
Table 1 below shows a summary of the control treatments each year.
Table 1 – Summary of control treatments at Upper Ugie Mainstem
| Year |
Invasive species |
Control work completed by |
Control work – date and method |
| 2018 |
Japanese knotweed |
Project staff and volunteer |
August – foliar spray |
| 2019 |
Japanese knotweed |
Landowner |
August – foliar spray |
| 2020 |
Japanese knotweed |
Landowner |
August – foliar spray |
| 2021 |
Japanese knotweed |
Landowner |
August – foliar spray |
4. Results
4.1 Invasive species abundance
Monitoring was undertaken at a single point at the site each year and the abundance of the Japanese knotweed was recorded using the DAFOR scale*. The abundance of Japanese knotweed was recorded as ‘dominant’ in 2018, ‘occasional’ in 2019 and ‘rare’ in both 2020 and 2021, with only a few stunted stems re-growing in later years (see Figures 1a and 1b).
The abundance of invasive species was measured using the DAFOR scale and is shown in Table 2 below.
Table 2 – Annual Japanese knotweed abundance from surveys (2018 – 2021) at Upper Ugie Mainstem
| Site Name |
Japanese knotweed abundance by year (DAFOR* scale) |
| |
2018 |
2019 |
2020 |
2021 |
| Upper Ugie Mainstem |
D |
O |
R |
R |
* – DAFOR Scale of abundance – D = Dominant (50 – 100% cover), A = Abundant (30 – 50% cover), F = Frequent (15 – 30% cover), O = Occasional (5 – 15 % cover), R = Rare (<5% cover)
Figures 1a & 1b: Japanese knotweed at Upper Ugie Mainstem site in 2018 and 2019
