Infestations of destructive plant Japanese knotweed springing up around Cornwall and growing out of control and causing structural damage to homes as their values plummet can be swiftly dealt with, one of the UK’s leading experts in the field has said.

Towns around the county — from Falmouth to Penzance, Camborne, Redruth and St Austell — have been hit by the ferociously growing import, that can expand by as much as 20 cm a day during peak growing season. Homeowners are at a loss to know what to do in battling the invasive species brought into the UK in the 1800s as a decorative plant, because nothing seems to kill it off.

Simply slashing the weed back as far as possible to the roots will achieve little, experts say, as it will quickly shoot back up and start rapidly growing all over again. This is due to its hardy and extensive root system that simply keeps sending up new shoots when what’s above ground is cut off.

“There’s no doubt that homeowners in Cornwall are faced with a seemingly impossible task when they try to get rid of Japanese knotweed in their gardens and elsewhere on their properties,” Nic Seal, MD and founder of specialist Japanese knotweed eradication firm Environet, told The Packet.

“It’s only natural that people think they can deal with a weed in their gardens themselves, but you have to bear in mind that this is no ordinary plant, and unfortunately, Cornwall is now a hotspot for this troublesome non-native species,” he said.

Environet, which is based in Woking, Surrey, and works on private and commercial premises all over the country to control Japanese knotweed, has invested heavily to find new and effective ways of killing off the “botanical bully” for good. It’s not only that it grows incredibly fast, but there are real property and legal concerns connected with it, too.

In its quest for unstoppable growth, the plant can identify cracks in walls and grow into them, potentially damaging otherwise solid structures. Homeowners in Cornwall also need to be aware that it’s illegal to let Japanese knotweed on their property spread to neighboring land or homes.

To perfect their ways of getting rid of Japanese knotweed, Environet purchased a plot of knotweed-infested land in Surrey. They specialise in removing the root and rhizome system from the ground, using their Xtract™ method on commercial premises and their Resi Dig-Out on residential properties. Their Xtract™ method is patented here in the UK as well as in the United States and Canada.

Essentially, Xtract™ is a specially designed screening and sifting machine that removes Japanese knotweed from an infested site in a number of days. With herbicide treatments, it can take years to kill off the plant without any certainty as to when the complete kill is achieved. Removal using these methods is more reliable and quicker than herbicide treatment and about 50% of the cost of alternative excavation methods, said Seal.

It is also against the law to improperly dispose of Japanese knotweed — as in just dumping it out in the wild, where it would start growing again. Careful legal compliance is essential, making physical excavation something that should not be tried by amateurs, cautioned the Environet boss.

For its part, Cornwall Council says it is working to help stop the spread of Japanese knotweed in towns and on land around the county. The council is cooperating with the Centre for Agriculture and Biosciences International, a global environmental organisation based in Wallingford, Oxfordshire, to find natural ways of controlling the plant.

So far, and with a £500,000 research budget, a type of “jumping lice” called a psyllid that feeds on Japanese knotweed and fungus has been identified as a possible solution to the growing problem.

The council says grants are not currently available to help people in Cornwall to professionally eradicate Japanese knotweed, “although its control may be funded through aid to some larger projects and grant schemes”. Anyone who spots the plant is asked to immediately report it via the nationwide Plant Tracker app or, if it’s growing on council land to fill out an online form.