South: Environet warns about Japanese knotweed

Although Japanese knotweed was introduced into the UK from Japan in the 1840s as an ornamental plant, it is now number one on the list of the UK’s most invasive plant species, costing around £166 million a year to control. Described by the Environment Agency as "indisputably the UK's most aggressive and destructive invasive plant", it causes structural damage to buildings, creates legal disputes between neighbours and can prevent the sale of residential properties.

As a warning, leading Japanese knotweed removal company Environet has cited the case of a landlord planning to build an extension at the back of his property, who discovered knotweed growing there. His tenants had mowed the original area of knotweed, spreading it in the grass cuttings. The knotweed was unsuccessfully treated with herbicides, resulting in new stunted plant appearing, which ruled out using herbicide treatment again, so the weed had to be physically removed by a specialist company.

Environet proposed its Resi-Dig-Out method, which took a couple of days to complete. But as the neighbouring properties also had a knotweed problem, a vertical root barrier had to be installed along the boundary to prevent encroachment. This work was supported by a five-year insurance backed guarantee, underwritten at ‘A’ rated Lloyd’s.

Nic Seal, founder of Environet, explained: “Physical removal is required when building works are planned over a knotweed infested area as it’s far more likely to eradicate this invasive plant than herbicide treatment. Just make sure you use a reputable company which can provide an insurance-backed guarantee for the work.”

There is now an insurance product available for property buyers concerned about the risk of knotweed. The Japanese knotweed indemnity policy provided by Countrywide Legal Indemnities covers the buyer and the lender for the cost of treatment and repairs if knotweed is subsequently discovered or recurs at the property.

It also covers any legal defence expenses should the knotweed spread to a neighbouring property, as well as any loss in market value, as a result of knotweed treated under the policy, when the homeowner comes to sell the property.