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Digging Japanese knotweed out of the ground is the most effective way to preserve a property’s value, new research carried out by YouGov for Environet UK shows.

The study also found that homebuyers were less reassured if a knotweed infestation has been herbicide treated – meaning it could recur.

Earlier this year The Royal Institute of Chartered Surveyors (RICS) relaxed its guidance to encourage herbicide-based methods of dealing with Japanese knotweed, which aim to control the plant rather than eradicate it, but the research shows that buyers would be considerably less comfortable purchasing a property where there’s a high chance the plant is still present and induced into dormancy. This could potentially affect their willingness to buy the property and the price they are prepared to pay.

Herbicide treatments can only be carried out during the growing season, (May to September), and can take two to three years to complete. The root system remains in the ground and can be prompted to regrow if disturbed, such as through landscaping or building work.

Excavation of knotweed can be carried out at any time of year and is the most effective way of dealing with the problem, removing the rhizome from the ground with immediate results.

While there is often a ‘knotweed stigma’ impacting the appeal of properties affected by the invasive plant, as long as an infestation is professionally treated with an insurance-backed guarantee, mortgages can be secured and sales can proceed.

Worryingly, 28% of people who stated they would not be concerned to discover knotweed on a property after they had bought it, believe they can treat the problem themselves.

Knotweed’s extensive underground root system makes it notoriously difficult to remove and it can regrow from a tiny fragment left in the soil, which is why mortgage lenders insist on evidence of professional removal and guarantees for the work before they will offer a loan on an affected property.

The best way to preserve a property’s value is to professionally excavate the infestation, secure a ten-year IBG and be honest and up front with potential buyers.