Pest Control – Containing Japanese Knotweed Claims

We are still seeing a high number of Japanese knotweed claims against surveyors; the product of much anxiety around JKW, which seems to have steadily increased since the turn of the millennium, reaching fever pitch over the past few years with photographs showing JKW growing through concrete and stories of destruction and loss of value to property.

In addition to the criminal and planning offences, we have seen a spate of claims in nuisance, claims against vendors for misrepresentation and professional negligence claims against surveyors. The main problem with JKW, which differentiates it from other invasive species, is that it is difficult to eradicate.

A number of bodies had provided some guidance on the issue of JKW, starting with the Environment Agency in 2006, which published a best practice paper entitled "Managing Japanese knotweed on Development Sites" and culminating with the RICS Information Paper published in 2012 (now out of date and soon to be replaced).

However it seems that the hysteria is now, finally, being countered. A number of studies have concluded that the empirical evidence does not support the panic associated with the plant. Leeds University carried out one such study in July 2018 that found no evidence to suggest that JKW causes significant damage to buildings, even when it is growing in close proximity to them. In fact, the study concluded that the plant caused "no more damage than other plant species that are not subject to such stringent lending policies" and concluded that the 7 meter rule was not a statistically robust tool for estimating likely rhizome extension.

Swansea University also carried out a study, assessing the efficacy of treatments. The media grossly over-sensationalised the findings as having concluded that JKW could not be eradicated. In fact, the paper concluded that complete eradication did not appear possible until after 3 years and that the use of glyphosate herbicide along with knowledge of the appropriate dosage, timing of application and adequate coverage were the most important factors for successful control of the plant.

On 16 May 2019, the House of Commons Science and Technology Committee ("Committee") published a report entitled 'Japanese knotweed and the built environment'. This noted that there was surprisingly little academic research on the physical effects of JKW on the built environment, notwithstanding the effect that its presence allegedly had on property values and...