It is the dreaded Japanese knotweed time again. All around the peninsula there are clumps slowly taking over hedgerows and drainage ditches. The worst area I have seen so far is near Quigley’s point on the main Derry road. From a distance it looks like a hedge and it seems to be growing wider every year. Japanese knotweed thrives on disturbance and has been spread by both natural means and by human activities such as fly-tipping and transportation of soil as only a fragment of the plant is needed for reproduction. Japanese knotweed reproduces by regenerating rhizomes and fresh stems. The rhizome system may extend from a parent plant up to 7 metres sideways and to a depth of 3 metres. Very small fragments of rhizome (as little as 0.7 g) give rise to new plants. Stems in water may produce viable plants within 6 days and can live quite happily in a jar full of water with no air in it, showing how invasive it is.
CONTROL
Japanese knotweed is not an easy plant to control. It may be cut using a lopper, brush-cutter or you can try burning. In amenity areas, frequent mowing keeps it in check. The young shoots of the plant are palatable to sheep, goats, cattle and horses and grazing may be used in suitable situations to keep the plant under control. This will not eradicate Japanese knotweed and the plant will continue to grow once grazing ceases.
The extensive underground rhizome system sustains the plant even when top growth is removed. Therefore, the aim of any control programme should be to target the rhizomes. This is best achieved using a chemical treatment. Translocated herbicides such as glyphosate and 2,4-D are used but have little effect. In areas where there is no risk of run-off to watercourses and where no sensitive vegetation (including trees and shrubs) will be affected, the herbicides triclopyr, picloram and imazapyr are sometimes used. These are persistent in the soil and may delay planting of replacement species.
As Japanese knotweed regenerates vegetatively, any waste material, such as that arising from cutting, mowing or excavation, should be disposed of very carefully. The use of equipment, which is likely to result in further spread of Japanese knotweed, such as a flail mower, is advised against.
Here is another idea- bringing in a predator
Horticultural.
