Key inspection considerations when it comes to Japanese Knotweed
So what are the ‘key’ features of a professional site inspection for Japanese knotweed? For property professionals and homeowners alike, listed below are some key points you should expect to discuss with the qualified specialist you bring on site assuming you are unfortunate enough to have Japanese knotweed on your land!
Qualified Japanese knotweed surveyors are aware of their duties and responsibilities to their client and others who may rely on their report (i.e mortgage lenders). So the first thing they are likely to tell you (somewhat counter-intuitively) is what they CAN’T see (usually within a section of their report called ‘Limitations’). Japanese knotweed is a plant that (to the trained eye) should be ‘easy’ to see and identify. But there are a multitude of reasons why it may be ‘present’ above ground, but not visible, for example; through prior works such as. cane removal, ground clearance or lack of access on overgrown sites.
Crucially, unless otherwise specified on instruction, most PCA members will assume the site inspection is by visual means-only. This means that dormant knotweed rhizomes in the soil can be missed (e.g. a winter survey or knotweed not growing due to past treatments or, worse, deliberately hidden). We recommend clients discuss the value/need for some trial pits when giving instructions. In certain situations, a hybrid approach can work well identifying critical areas on the site and conducting soil investigations ‘as required’ rather than a scatter-gun approach.
If Japanese knotweed has been found during the inspection, it needs to be clearly and accurately mapped. Such ‘plans’ are an important marker for future reference by a variety of stakeholders and other property related professionals! We recommend such plans show not just the Japanese knotweed visible, but indicate the likely and ‘worst-case’ spread of the rhizome network in the soil too.
These so-called ‘buffer zones’ are always indicative. No assumptions should be made about boundary encroachment liability until some soil inspections are conducted... and the best time to do this is during the initial inspection. On development sites, the volume of soil excavated can be significantly reduced by having a qualified CSJK clerk of works directing the dig until all the rhizome is found and stockpiled or removed.
The optimum Knotweed Management Plan (KMP) may not seem to be relevant to the site inspection but any qualified CSJK surveyor will want to know before or during their site visit what factors may limit or determine the options available for remediation of the knotweed. This could be something as simple as budget or the precise planned location of buildings; issues of timing (you can’t spray knotweed in January!), but really, everything is pertinent!
Control or Eradication? By way of an example to support the last point, every Japanese knotweed site inspection which is conducted with a view to evaluate site management options should have a context i.e. what does the client need to, or want to, achieve?
In domestic or commercial settings, it may be acceptable to manage the Japanese knotweed in situ, e.g. by herbicide spraying; especially in large gardens/plots, no development plans and where this options enables the issue of a Guarantee/IBG . The client may even give specific instructions to prevent disturbance of surrounding vegetation. But eradication (normally meaning physical removal of all soil/rhizomes) will usually entail a different approach. This approach may include considerations of access for large machinery and also careful planning to limit pathways for spread during remediation.