TECHNICAL BULLETIN
ISSUE 29
JULY 2018
JAPANESE KNOTWEED A SURVEYOR’S PERSPECTIVE DAVID GREGSON, B.SC., M.R.I.C.S., M.A.E.,C.BIOL., C.ENV CHARTERED SURVEYOR, BIOLOGIST, ENVIRONMENTALIST
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Following research by Dr Dan Jones, Chartered Surveyor, Biologist and Environmentalist, David Gregson considers its impact on property professionals moving forwards. As a residential surveyor providing surveys and valuations for purchasers, I have based my working practices regarding Japanese knotweed on the received wisdom and general guidance available to the profession.
The underground spread of knotweed roots spans up to seven metres from the edge of the emerging stems. They are usually at a depth of about one metre but can reach down to three metres deep.
Lender perspective
This can be summarised as follows: 1. Various methods of treatment are available, some of which are more or less environmentally acceptable than others. 2. A variety of different herbicides are claimed to be effective in the treatment of Japanese knotweed. 3. Some herbicides with anecdotally good results in controlling JKN have been withdrawn from the market due to perceived environmental risks, the most important of which are picloram-based synthetic auxins. 4. Rhizome-removal and soil cleaning is a treatment advocated by large firms in the sector. 5. Hand pulling of emerging knotweed stems is preferred by some as the most environmentally-friendly method. 6. Where chemicals are used, once the stems stop emerging from the ground following treatment and for a period of two years afterwards, the rhizomes are considered dead, and the problem eliminated.
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The reaction of lenders to properties affected by Japanese knotweed does vary, but it is possible to obtain a mortgage on a property where Knotweed is present. However, lenders will treat each case individually, taking into account the cost of eradication and the effect on saleability and value. In making these judgements, they will consider other factors impacting on the property. For helpful information on this, see the RICS Professional Information Paper on Japanese knotweed and Residential Property 1st Edition, published in 2012 and written by Phil Parnham from BlueBox Partners. Generally, lenders willing to provide finance will seek a commitment of advance funding for a three-to-four-year treatment programme by a company able to offer a warranty. Many such companies are members of the Property Care Association.
Past and present research
It would be reassuring if all our knowledge about Japanese
