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IMPORTANT - Japanese Invasion

What Is Japanese Knotweed?

Japanese knotweed (Fallopia japonica) is a strong, clump-forming perennial with bamboo-like stems of over 2m which regrow each year. It produces leaves of up to 14cm in length and 15cm-tassels of flowers in late summer and early autumn.
The plant was brought here from Japan for its ornamental qualities. ‘Since it was introduced into the UK in the mid-nineteenth century Japanese knotweed has spread across the UK, particularly along watercourses and transport routes such as railway lines,’ says Leigh Hunt, Principal Horticultural Advisor, RHS.

Why Is It A Problem?

Japanese knotweed is a nasty piece of work, and it’s not going away. Though it can be treated, the invasive plant is unlikely to disappear entirely from our shores. ‘We can't get rid of it, we have to learn to live with it and control it,’ says Maxime Jay, MD of specialist knotweed consultancy and remediation company
Knotweed And Mortgage Lenders


Above left: Japanese knotweed in the summer. Above right: in the winter Japanese knotweed can look like it's dead but the leaves will come back in the early spring/summer.

Mortgage Lenders: If you're buying a new home and Japanese knotweed comes up on the survey, a lender may refuse your mortgage. 'In practice, it's not usually a problem as long as a remediation plan is put in place,' says Sue Anderson, spokesperson for the Council of Mortgage Lenders (CML).
It's clearly a worry for prospective home owners. 'We get 15 to 20 calls per week asking for advice on Japanese knotweed, often when a valuation for mortgage is made,' says Maxime Jay. 'The problem is that every mortgage lender has its own policy.'

Surveyors: To give surveyors a clear guideline on risk assessment regarding Japanese knotweed, a working party has now been set up, chaired by the Royal Institution of Chartered Surveyors (RICS) and involving the Council of Mortgage Lenders (CML) and contractors, including Musketeers Group. 'RICS recognise the problem and are working with members of the treatment industry to come up with an agreed way forward. CML and The Building Societies Association (BSA) are aware of this and support this initiative,' says Stephen Morgan, spokesperson for RICS.

Developers also need a consistent approach when knotweed is found on site. 'The method could be a traffic light system similar to that already used in Cornwall. Ideally, even a red light wouldn't mean building was an impossibility,' says Andrew Cooper, Senior Project Manager, Musketeers Group.

How Can I Tackle It?

'Japanese knotweed is known to be a very invasive and difficult-to-kill weed,' says Leigh Hunt. 'If you do see it in your garden, it is best to try to eradicate it before it begins to colonise the whole plot. Digging out can be tried, but is rarely successful and the remnants should be burnt on site. The most practical solution is to use a strong glyphosate-based weedkiller but, even with this, several treatments are usually necessary.'

• Spray with glyphosate weedkiller in May, when the plant is around 90cm high, then apply again in mid-summer and once again in September before it begins to die down in autumn. Keep the spray away from garden plants.
• Any bushy regrowth needs to be re-treated.
• You’ll need to work at this for several seasons to get results, though professional companies, using powerful weedkillers, can cut the time.
Dig It Out
• Although taking a spade to knotweed is effective (removing as much of the root as possible), the results won’t last long as it usually regrows.
• Repeated attempts will be needed for seasons to come.
• Burn on site. If you choose to remove it, the plant is classed as 'controlled waste' under the Environmental Protection Act 1990, and should be disposed of at a licenced landfill site. Never include it with normal household waste.

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