Map shows plant’s hotspots
A NEW map showing the most up-to-date Helensburgh and Lomond hotspots for the destructive Japanese knotweed plant have been revealed.
Native to East Asia, Japanese knotweed was introduced to the UK in the 1800s and has since become one of gardeners’ most dreaded invasive species.
It can grow up to four inches a day and forms dense thickets which can kill native plants and damage infrastructure.
Japanese knotweed is identified by red stems and a bamboo-like appearance. It can grow up to eight feet tall, though its roots can be as long as 28 feet.
According to research by invasive plant specialists Environet, there are 45 recorded occurrences of Japanese knotweed within a four-kilometre radius of Helensburgh town centre itself.
The A818 between the town and Arden also has a high concentration of the plant, with 39 cases within 4km of the town and another 26 within a 4km zone around Arden.
There are 39 cases within 4km of Rhu and Shandon, and 27 within 4km of Garelochhead.
Cardross has 25 instances within 4km of the village centre, and there are another 18 within 4km of the Rosneath peninsula.
In Arrochar, there are 12 cases within 4km, and there are 10 within 4km of the Ardlui area.
Many of these cases, however, will be duplicates, as the ‘within
4km of Helensburgh’ zone, for example, overlaps with ‘within 4km of Rhu’.
If Japanese knotweed is found on private property, the law states that the land owner must take the necessary steps to prevent any further growth.
Those who come across Japanese knotweed should not cut, mow, or trim the plant as it will grow back from the root - and there’s also a high risk of fragments of the root or stem growing into a new plant.
The only way to be sure of killing the plant is by applying herbicides over the course of several years.
A spokesperson for the Scottish Invasive Species Initiative said: “Due to its persistent rhizomes and ability to regenerate, research suggests the only effective way of controlling knotweed is by herbicide (glyphosate) application.
“Treatment is needed over subsequent years. While initial success can be achieved in the first year, at least some of the root will remain and will grow to form a new stem if the treatment isn’t followed up in years two to three.
“The average time for a chemical treatment programme is three to five years.”
For more information on how to deal with Japanese Knotweed and to report a sighting to the Scottish Invasive Species Initiative, see www.invasivespecies.scot/japanese-knotweed.
To see Environet’s full map, visit www.environetuk.com/exposedjapanese-knotweed-heat-map