Knotweed scourge continues unchecked

The website www.invasivespeciesireland.com has identified Japanese knotweed as one of the most unwanted invasive plant species in Ireland.

 

Fallopia japonica, as it is also known, is rapidly taking over our hedgerows. It can grow through concrete and damage property as well as killing forests and woodlands by cutting out the light at their edges.

Last year, The Irish Times reported the plant is taking over unfinished housing estates in Kerry and threatening serious damage to building by growing through concrete and tarmac. In the UK, it is estimated its clearance costs £1.5 million each year.

If you have Japanese knotweed on your land, there are some things you should not do:

Do not strim it: this is the worst thing you can do because it creates millions of tiny pieces, all of which can grow into new plants.

Do not attempt to dig up the rhizomes: even 1cm of rhizome can produce a viable plant so if you disturb the soil you risk spreading broken pieces of rhizome further.

Do not cut it back and leave the cuttings on the ground: these will quickly spread in the wind, in water, on car tyres and on animals and each piece can form a new plant.

Do not compost cuttings or put them in the rubbish bin or take it to the dump: it is an offence under the Wildlife (Amendment) Act 2000 to knowingly grow or disperse Japanese knotweed so if you dispose of it carelessly, you will be breaking the law.

Do not cut the canes and then pour herbicide down the cut end: this has become popular but it does not work because as soon as a Japanese knotweed cane is cut, that part of the plant shuts down and it will not take up the herbicide.

Do not ignore it: a small Japanese knotweed plant quickly becomes a major infestation.

What can you do?
Herbicides can check its growth but only the most powerful chemical treatments will eventually clear it. These are unsuitable for spraying near water.

One approach is to allow the weed to grow to about 1m, in early summer, and spray then. You will need to respray regrowth in midsummer and again in September if necessary. Invasivespeciesireland.com has produced best practice management guidelines online with information about appropriate herbicide use.

Injecting each cane with a systemic herbicide is more effective than spraying and much less environmentally damaging. The Japanese Knotweed Control Service (www.japaneseknotweedcontrolservice.com) is a service based in East Clare that offers an eradication programme using this method. They have demonstrated it is possible to achieve 98% eradication in one season at an affordable price. For further information, contact 061 924 287.

Go to Alien Alert on the www.invasivespeciesireland.com website and report sitings of Japanese knotweed. Invasive Species Ireland is a joint venture between the Northern Ireland Environment Agency and the National Parks and Wildlife Service. It provides important information about the threat of invasive species and encourages everyone to get involved in tackling the problem.

Talk to your neighbours and work together to identify potential contamination routes and how you can minimise spread. Once you have eradicated Japanese knotweed from your own land you may be unable to prevent reintroduction without co-operation from adjacent landowners.