Knotweed Services (UK) Ltd were contacted by the client to organise a site survey on a residential property in Norfolk which is located on a quiet country lane. The client informed us that JKW had been found on the private driveway at the front of property. Whilst at the time of call, our client mentioned he wanted the most cost effective way of treating the Japanese Knotweed.
Back in 2016 when I attended a site survey in Norfolk, I identified 2 zones of JKW where 3 strands of JKW were present on a private driveway. Whilst zone 1 and 2 were not close to either property/other inhabited structures, it was possible that, if left untreated, as the JKW matures, that the Knotweed would start to pose a risk to the structural integrity of the perimeter wall in the near future – for this reason the Japanese Knotweed infestation was categorised as a Category 3 Risk in accordance with the most recent RICS guidelines (full guidelines on our website). I therefore advised that further investigations should be done by an appropriately qualified or experienced person into whether the Knotweed had caused any damage.
At time of survey, JKW was not present on the neighbouring property, however I informed the client to contact the neighbours so that they were aware of the situation to prevent the weed spreading further (not disturbing the soil).
I recommended treating the JKW at the property once in summer 2016. If we had have left it any longer, it could have lead to serious structural damage being done to the wall/driveway. Herbicide treatment was my advised treatment using a mixture of spraying and stem injection methods. From notes from call, I also noticed the client was looking for the most cost effective method to treating the JKW in which a 5 year herbicide treatment plan is cheaper. I recommended that a crown removal would be best later in the year. I informed at time of survey that effort should be made to not disturb the soil as that would most likely cause the JKW to spread, worsening the situation.
The mapping stage of our plans is crucial to identify the location of the infestation. This not only helps to indicate the proximity to boundaries/habitable space & outbuildings and the associated RICS classification, but also identifying the possible migration (7m buffer zone).
See Figure 1.
On my visit to treat the Knotweed in September 2016, the stands were protruding onto the driveway so the client had tied the canes back to avoid disruption. This had been done very well and I believed it would greatly reduce the risk of it spreading.
There were 2 mature stands and 1 immature stand which were either hand held sprayed or stem injected with glyphosate based herbicide.
On my first visit in July 2017, there was no signs at all of regrowth’s suggesting the treatments had been very successful.
All canes were dry and brittle from 2016. I observed no damage to the driveway or border wall. 2 large rubble sacks of canes were cut down and burnt off site. The treatment plan appeared to be working very well so I suggested continuing as planned. When I returned back in October 2017, no treatment was required, my visit was to make sure no griefs had occurred late in the season. I recommend returning in July 2018 to survey for new growths.
I returned back in July and no growth was observed on site. The crown and associated rhizome was removed for aesthetic reasons only. The material removed was typical of that a rhizome which had begun to degrade. The bright orange colouration normally expressed a healthy plant as been replaced by a brown woody colour. Rhizome removed was brittle and dry. For one crown, woodlouse were seen all around the rhizome suggesting they may be feeding on woody remains. Based on these observations I was confident that the treatment process had been successful.
Overall the Knotweed at the site had responded remarkably quickly to the treatment in 2016. The visit marks the second year without any growth. Consequently, I informed our team in 2018 that warranty could now be issued.