Garden nuisance can’t be killed off, say scientists
HOMEOWNERS have been told there is no end to one of their worst garden nightmares – with scientists proving the dreaded Japanese knotweed cannot be killed off.
Researchers have spent five years on the world’s biggest study at two sites in South Wales to test different ways of annihilating the invasive weed, but have come up empty handed.
The bamboo-like shoots plague gardeners because it grows at an incredibly fast rate and chokes other plants.
But it is incredibly hard to control, as its underground roots grow stronger and faster than the above-ground plant visible to gardeners.
Scientists conducted the world’s biggest ever study into eradicating the plant at two sites in Taff’s Well, near Cardiff, and in Swansea. But despite using various chemical solutions, physical projects and a mixture of the two, the scientists found no definite ways of killing the plant completely using current methods.
Professor Dan Eastwood, from the Swansea University project, said: “Basically, we’re discovering how best to tackle invasive plants in real world conditions, informed by evidence of what actually works. We began focusing on knotweed at a time when there was a great deal of hysteria surrounding it.
“At the time, most information for people affected by the plant was largely based on anecdote. This led to the prospect of unscrupulous companies offering expensive and ineffective treatment solutions. It was incredible to us that there was no long-term, large-scale field trial analysis of the treatment methods used to control Japanese knotweed.”
And Dr Dan Jones said gardening companies who claim to be able to eradicate the plant were not fully accurate.
He said: “Off the back of the first three years of data we’ve found that eradication is not possible. Hopefully over the longer term we may move towards that by using new chemicals we’re looking at. But it’s not a question of eradication, it’s a question of sustained control and management and well informed control and management.
“Claims made by companies, stating that they could eradicate Japanese knotweed using herbicides in short spaces of time have now been proven to be false, based on our experiments.Furthermore, we have shown that applying the wrong herbicides at the wrong time of the year leads to greater herbicide use and environmental impacts.”
Dr Jones said the best chemical to control the knotweed was glyphosate – but the herbicide is feared to pose a risk to other wildlife too.
He added: “There’s a range of issues in terms of risk and hazard. There’s a political issue around glyphosate as well. What we’ve done is work with the biology of the plant to minimise the amount of herbicide we’re using over a treatment life cycle.
“Although we’re using quite a contentious herbicide in that respect, we are using far less of that herbicide than you would use for other products that don’t work on Japanese knotweed.”
Househunters looking at homes in areas dense with Japanese knotweed can often struggle to secure mortgages, over fears the roots could cause structural difficulties to buildings.
Chartered surveyor David Gregson said: “The main problem is mortgage lenders are very reluctant to lend on properties where knotweed is present and obviously that means in turn people can’t sell their properties and it might sometimes be because knotweed is present in the next door garden.
“A typical situation is a couple wanting to get divorced. They’ve got a lot of knotweed in their garden, they both want to move on with their lives and they’ve got a house they can’t sell.”