Japanese knotweed infestation in County Clare

JAPANESE knotweed is a tenacious invasive plant species that is infesting the county at an extraordinarily fast rate and becoming an increasing nightmare for landowners, developers and those responsible for the safeguarding our environment. 
Japanese knotweed (Fallopia japonica) grows like a triffid forming tall dense thickets that exclude other vegetation; shuts out the light at the edges of woodlands and forestry; eliminates native plants in hedgerows; damages flood defence structures along rivers and can seriously damage buildings and concrete surfaces. 
In February 2011, The Irish Times reported that Japanese knotweed 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 that its clearance costs £1.5 million each year.

How to spot Japanese knotweed
In the spring, Japanese knotweed shoots are dark red in colour and quickly form bamboo-like stems from which sprout green leaves shaped like shields. It can reach up to 3m and more in height and in summer, it has spikes of small, creamy white flowers. It sheds its leaves in autumn to leave dead, light-brown hollow stalks that look similar to bamboo. It grows by underground stems (rhizomes) that are thick and knotty, which are bright orange inside and snap easily, like a carrot. The rhizomes of a single plant can reach a depth of 5m and spread horizontally for 20m forming multiple shoots along their length. These rhizomes are almost impossible to eliminate.

What not to 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 broken pieces of rhizome spreading 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 ignore it. A small Japanese knotweed plant quickly becomes a major infestation.

What to 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 plants to grow to about 1m and then spray in early summer.You will need to respray in midsummer and again in September if necessary. Invasive Species Ireland has produced Best Practice Management Guidelines online with information about appropriate herbicide use (www.invasivespeciesireland.com).
One of the safest and most effective control methods is to inject individual Japanese knotweed canes with specific herbicides using injector equipment. The head gardener at Birr Castle reports successful use of this method even over large tracts of land. In the UK, local landowners, the county council, the National Trust and other agencies have used this method to restore a beautiful valley that was previously infested. Check out www.stoptheknot.com for more information on injection control.
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 and 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.