Group gets to root of knotweed issue

A small, dedicated group of people is fighting a successful battle against an invasive species which is capable of destabilising houses.

Group gets to root of knotweed issue

The group in Glounthaune, Co Cork, could be described as best in class when it comes to tackling Japanese knotweed, which is becoming a scourge in many communities.

Glounthaune Tidy Towns members identified 80 of the plants in their area and were so concerned that they set about eradicating them, which meant they had to inject every one of the plants’ 120,000 stems.

Tidy towns chairman Conor O’Brien said they purchased three special stem injectors in Britain, which cost €800 each and set about the task of tackling the plants.

Knotweed is very hard to kill as the roots go three metres deep and form a radius of seven metres around each individual plant from which new plants can spring.

“Roots can grow through concrete and can be very destructive to property. Indeed in the UK its presence will prevent a mortgage being granted on a property,” Mr O’Brien said.

He said stem injection with Glyphosphate (such as Roundup Biactive) is the tidy towns organisation’s preferred method for killing knotweed.

“Stem injection is very effective. It requires a specialist injector gun, but is very labour intensive,” he said.

Mr O’Brien said it’s widely accepted that Glyphosphate herbicides are the most effective especially if administered in September/October when the plant is retrenching to the root system on the onset of the first frost.

Locals decided to act after an adverse comment in the 2014 Tidy Towns adjudication report which mentioned the “astonishing amount of knotweed in Glounthaune”. They carried out a survey in October 2014 covering a distance of 6km along the old N25 route (which also tracks the Cobh- Midleton railway line) and found nearly 80 individual knotweed plants.

“We discovered that 98% of the knotweed is on public land. We carried out trials using the stem injection technique early in October 2014. This resulted in almost 100% effectiveness when inspected this year,” Mr O’Brien added.

Members of Glounthaune Tidy Towns committee near some of the dead Japanese knotweed canes which the organisation is successfully eradicating. Pictures: Denis Minihane
Members of Glounthaune Tidy Towns committee near some of the dead Japanese knotweed canes which the organisation is successfully eradicating. Pictures: Denis Minihane

“A number of the tidy towns committee attended two alien invasive species seminars/workshops one sponsored by IRD Duhallow, the other by SECAD (South East Cork Area Development). We recruited three teams of two to be trained locally in the stem injection technique,” Mr O’Brien said.

The organisation has spent around €8,500 so far eradicating the plants. It received financial support from Cobh Municipal area .

“We erected signs at all locations where we spotted knotweed to stop anybody inadvertently cutting them.”

Mr O’Brien believes the knotweed was brought to the Glounthaune area by the Beamish brewing family, who owned Ashbourne House, in the late 1800s.

Japanese knotweed evolved on the higher slopes of volcanoes in Japan where the harsh conditions forced the plant to develop deep roots to survive. Even a tiny sliver of the plant when cut is enough for it to regeneratate.

“It has been shown that a snippet of root or rhizome as small as 0.7g will produce viable plants,” Mr O’Brien said.

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