たたきなさい    JAPANESE KNOTWEED    イタドリ
 
in the Lyreacrompane area

                                             Dealing with an Invasive Plant

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What is Japanese Knotweed?

    
A worldwide invasion!!! which can grow through tarmac

These photographs show Japanese Knotweed in full bloom and as a young plant forcing its way up through tarmac. It is a rhizomatous perennial that can grow rapidly to a height of up to 10 feet.  The roots of a single plant can extend for 20 feet and can be found 6 feet below the surface!!!

Red/purple shoots appear in early spring. As the canes grow, the leaves unfurl and the plant turns green.  Mature canes are hollow and have a characteristic pattern of purple speckles. The leaves are carried on stems in a distinctive zig-zag pattern. Flowering occurs in late summer/autumn and consists of clusters of creamy white flowers.  During the late autumn and winter, the canes lose their leaves and turn dark brown. The dead canes remain standing. The plant lays dormant underground for the winter and reappears again in the spring.

     
A close look at the leaves and Japanese Knotweed in full flower
 

Where did it come from?   Japanese Knotweed was introduced as an ornamental and fodder plant in the 1840s. It came into a new environment in Ireland without its natural enemies that keep it in check at home in Eastern Asia.

Other names for Japanese Knotweed are Sally rhubarb, donkey rhubarb, gypsy rhubarb, Hancock's curse, Pysen saethwr, Glúineach bhiorach, Mexican bamboo, Japanese bamboo, Japanese fleece-flower, wild rhubarb and crimson beauty.

Why should it be a cause of concern?  Knotweed is very invasive, totally out of character with the Irish landscape, overpowering native species and is of little value to wildlife. As in parts of Britain, Knotweed infests the banks of rivers as it is quickly dispersed by water.  The river Smearlagh in the Stacks/Glenaruddery Mountains of North Kerry is endangered in this regard – a matter of concern to anglers.

How has Japanese Knotweed found its way into the wild?   Luckily, Knotweed does not have viable seed (although there is a danger that cross pollination with distant members of the same botanical family such as Russian Vine may bring that catastrophe about).   The plant is spread by human activity.  Unfortunately, extremely small bits of the root will reproduce.  They are carried from site to site on the wheels and tracks of earth-moving machinery and on the wheels of trucks, JCBs and tractors. This is why you will often find dense thickets of Knotweed at gaps and entrances into fields and sites.

       

The River Smearlagh in Lyreacrompane, Co Kerry in danger of serious infestation and Knotweed in December beside a roadway and stream in Lyreacrompane.

Knotweed is also spread by illegal dumping in our bog lands, boreens and isolated spots.  This dumping arises out of generally vain attempts by people to remove the weed from their property – rarely successful, as the smallest piece of root or crown left behind will regenerate!   So now, instead of one infested site, we have two - and more in the making if the roots are dumped anyway near a river or stream.   The action of flowing water carries parts of roots down stream where at various locations they find landfall. 
What can we do about the  Knotweed invasion?  

The first task is to stop the matter getting worse and then begin to take steps to clean up yet another fine mess we have made of the environment.  Information and education on the problem is the first step.  So spread the word!!!

Digging.   Digging up the plant rarely succeeds, as   it is almost impossible to guarantee the removal of all root parts. Sections of rhizome (root) as small  as 0.7 of a gram can grow into a new plant.  (If digging is undertaken the material must be disposed of in a managed landfill site).

Japanese Knotweed in Limerick, Ireland looking fresh in Mid-November.  This was new growth following ground disturbance

Cutting downCutting the plant to the ground, a couple of times in late summer, with a loppers or a scythe (do not use a mower or a strimmer) will deprive it of the ability to convey nourishment to the roots.  Employing this method over a number of years will greatly retard the plant and will (probably) eventually kill it.  All stems cut down should be burnt on site or taken to a managed Landfill. (Do not include cut stems in home or Council composting projects.)

Clean down machines.    Drivers of earth moving machinery should get to know Japanese Knotweed and avoid contact with the plant when working on site.    Wheels and tracks should be cleaned down before leaving an infested site. 

Grazing.    Japanese Knotweed is palatable to sheep, goats, cattle and horses and grazing  may be used in suitable situations to keep the plant under control.  Some experts say there is evidence that persistent grazing (or cutting) in the spring can actually strengthen the roots and lead to a stronger re-growth if the practice is stopped.

Herbicide.   The most effective strategy against Knotweed is the application of a herbicide containing a formulation of Glyphosate in September.  Spring treatment is acceptable, but less effective.  This treatment should kill off Japanese Knotweed in three years. (Always carefully follow the instructions in relation to personal safety, other plants and use near water when using Herbicide.)

Japanese Knotweed hit be rust - a natural enemy in its native east Asian habitat

Biological Control.    Japanese Knotweed was introduced to Ireland without any of its natural enemies.  Trials are underway in Britain to identify safe and appropriate predators and pathogens that can be released into the environment for the purpose of debilitating the plant and thus make any subsequent control easier.  The outcome of these trials may take a number of years but hopefully they will produce results that will allow the Knotweed, which is inappropriately growing in the wild, to be treated.

Japanese Knotweed in Kerry, Ireland.

In the first instance, this webpage arose out of concern for the spread of Japanese Knotweed in the Lyreacrompane district of north Kerry, Ireland.  It is a moor land area in the Stacks Mountains. 

 

Illegal dumping and earth moving machinery have introduced Knotweed to this classical peatlands setting.  The rapid and quick flooding streams and rivers have taken the initial infestation and spread it further and further.

Through this webpage and other media we hope to establish the true extent of the infestation in all of County Kerry and to encourage individuals, organisations communities, local authorities and state bodies to work on the problem.

Tell the Carriers! 

Many drivers of earthmoving machines are totally unaware that they may be distributing Japanese Knotweed  as they move from site to site.  If you know any you should draw their attention to this webpage.

Help to survey the extent of Knotweed infestation in Kerry

Specifically, in relation to Kerry visitors to this site we would ask you to check out the problem on your area and e-mail us your findings.  Most of the Japanese Knotweed will be found along the road side and on the banks of streams and rivers.  This makes it relatively easy to track down.

Your survey should include

-the name of the stream or river and the part of it surveyed.

-the location of the stretch of road surveyed.

-the approximate  number of clumps in the stretch of river or road surveyed.

-information on the approximate size of the clumps, i.e. 5 feet by 5 feet, 10 feet by 7 feet etc.

-information on urban infestation would also be welcome.

E-Mail any information you collect to ramblinghouse@eircom.net

Messages

We would be delighted to carry your messages, opinions and accounts of your experiences with Knotweed in this column. You can e-mail them to us at ramblinghouse@eircom.net