Japanese Knotweed (F.japonica) is a problem. It is hugely invasive, can prevent you from selling your home and, indeed, mortgage lenders are unlikely to lend on a property which has it. Property Surveying has produced lots of advice on Knotweed and its issues, and certainly it is one of the many reasons you should seek a survey before buying property.
We know Knotweed is a problem, but on building land and on properties where it has been treated, life has gone on … extensions, new homes and commercial properties have been built, mortgage lending granted, hotel buildings, supermarkets and PFI buildings have been constructed.
A team of bioscientists at Swansea University, led by Prof Dan Eastwood and Dr Dan Jones, has concluded that “no treatment completely eradicated F.japonica” but that “a multi-stage glyphosate-based treatment approach provided the greatest control in the short term.
Listed by the World Conservation Union as among the worst invasive species, Japanese Knotwood is widely known among UK homeowners, mortgage lenders and housing developers as a potential major problem.
The controversial report has provoked a huge reaction from Knotweed experts, accusing the publishers of scaremongering and misleading homeowners. The experts assure us that if treated properly, expertly and patiently (we’re talking years), sleepless nights worrying about Knotweed can also be eradicated.
The Swansea University team’s own advice to homeowners:
- Ignore the hysteria – your house will not fall down. Knotweed can be controlled using glyphosate at the right time of year, though this can usually take three to five years. However, we don’t recommend you do this yourself – we have seen mortgages declined because of botched treatment undertaken by homeowners.
- Knotweed is a resilient weed that cannot be controlled by one herbicide treatment in a single year, a claim frequently made by unscrupulous companies. Any treatment strategy should be long-term and target both the above-ground and extensive below-ground parts of the plant.
- Effective treatment centres on working with the biology of the plant and targeting the correct herbicide when the plant is vulnerable to its effects, from summer into late autumn (depending on the weather).
- Calling out a weed control company to control knotweed is not the same as calling out a plumber. We would expect the plumber to get the work done soon, if not immediately. If you call out a company in spring to control knotweed, quite rightly, you will need to wait until later in the year to get the best results – this will save you time, money and hassle in the long-term.
- Once knotweed has been effectively controlled using herbicide don’t disturb this land by digging, for example, as it is likely to come back; even if the above-ground parts of the plant are dead, the below-ground rhizome system probably isn’t. Again however, don’t panic, if it comes back, call the contractors to regain control.
- Don’t try digging out the knotweed yourself, it is easy to miss parts of the root and spread it and you cannot dispose of this plant material along with your garden waste – in fact, it is illegal to do this.
The offending report was published in Biological Invasions: Optimising Physiochemical Control of Invasive Japanese Knotweed (Jones, D., Bruce, G., Fowler, M.S. et al. Biol Invasions (2018))
Biological warfare is a possibility with insects being trialled that will feed off Japanese Knotweed and hold it at bay.
Visit http://www.propertysurveying.co.uk to find a local Chartered Surveyor, if you think plant life might be threatening your home.