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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. Laboratories have come up with a biological solution to keep the Japanese knotweed from spreading and hopefully keep it under control. The weed up to yet has no natural enemies in this country so the plant can spread undisturbed. This is about to change as bugs and fungi that grow on the plants in their native country are to be introduced. The beetle eggs are injected into the stems and when they hatch they dig their way out into the open, the result of the tunnelling snaps the stems. The fungus will hopefully kill off the vulnerable plant. I suppose in a few years time we will be invaded with knotweed beetles eating the vegetable patch instead of the rabbits doing it and garden plants will be collapsing with a strange fungal growth, I’ll watch with interest. Japanese knotweed can live quite happily in a jar full of water with no air in it, showing how invasive it is. The other method that has been used for a while now is to cut each stalk and painstakingly inject each stem with herbicide, this will still take between 3-5 years to kill the plant. And to think all this started from one plant in a pot on someone’s doorstep at the turn of the century. Leaflet Clare County Council and The Heritage Council have produced a leaflet with advice on the control of Japanese Knotweed. Copies are available free-of-charge from the County Donegal Heritage Office at the address below. With best regards, Joseph Gallagher Heritage Officer, County Donegal Heritage Office, Donegal County Council,Station Island,Lifford, County Donegal. Telephone: (074) 917 2576 E-mail:
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We’re always looking for new delicacies to eat for free and the latest revelation is about Japanese Knotweed. The young shoots of this invasive plant are edible and can be made into wine, just substitute rhubarb with knotweed. The idea is to pick small asparagus looking tips from the knotweed plant and make them into wine, puddings, again like you would with rhubarb, either a crumble or a fool. Harvesting between now and May is the best time as the shoots are young and tender.
It’s estimated that in the UK alone it would cost £13.5 billion to eradicate the pest and has already cost £70 million to keep it off of the new Olympic site in London so we will have to do our bit to make sure we can keep it in check in Ireland.
Cutting the plant back weakens it and the plants will eventually die off so eating the plant will be a good idea all around. We haven’t tried this yet so if you feel brave and do it before us I would be delighted to know how you get on- check the internet for recipes and health and safety tips..
A couple of words of warning though; Knotweed will grow anywhere, even through concrete, asphalt and most importantly through sprays of herbicide. Make sure you gather it from places where you know the soil is clean and chemical free. The other thing will be to burn anything you don’t eat. The plant can grow from the tiniest piece left on the ground.