Japanese knotweed can cause your property value to fall

– Auctioneer and chartered surveyor, John Corridan, offers advice on Japanese knotweed –

FEW invasive plant species cause property value to fall in the way that Japanese knotweed does. Introduced to the UK by botanists in the nineteenth century the plant has gone on to become one of the most destructive and damaging of all invasive plant species.

Why is Japanese knotweed so destructive?

Firstly, its spread is rampant, the rhizome of a single plant can grow more than 1 metre vertically and 4 metres horizontally. Secondly, it is tough, it can break through tarmac, enter into cavity walls, block drainpipes. If it is not targeted early in its life cycle it becomes entrenched and treatment options become expensive.

How damaging is it to property values?

Many Irish and UK banks require confirmation on whether Japanese knotweed is present on property being purchased and mortgage approval can be turned down if a surveyor finds it on site.

A quick Google search reveals a number of knotweed nightmares. The UK, because of its housing density and media focus, is more alert to the threat than we are here in Ireland.

A case in Hertfordshire hit the headlines a few years ago when the value of a couple’s home dropped by more than £250,000 because of a Japanese knotweed invasion. The pair had only lived in the new build property for a month when they found the weed growing first into their garden, then up through the floorboards into their dining room.

A house in Broxbourne was initially valued at £305,000 until the knotweed was discovered – then the valuation fell to just £50,000.

Clean up costs for development sites

The cost to the London Olympics to remove Japanese knotweed from the 10 acre Olympic site cost more than £70 million.

Closer to home, at Kenmare hospital, works to remove the plant cost in excess of €100,000.

Local Authorities in Clare and Limerick have imposed stringent knotweed treatment conditions onto planning grants. Developers need to be very wary of the potential cost consequences of building on knotweed infested development land.

How it spreads

It takes no more than a thumb sized cutting of the plant to establish itself in new ground. Fortunately, the plant does not propagate by seed, it grows only when cuttings detach from the main plant and are carried along the road whether by persons or machinery. Needless to say the risk of spread is dramatically increased where the plant is cut as each plant segment can itself regenerate. The plant is also carried along the by water and the River Feale is particularly affected.

What not to do

Under no circumstances cut the plant. That will not kill it and serves only to spread the weed. Do not attempt to dig the plant and dispose of it. To dispose of an invasive plant species without licence is against the law and for good reason.

What to do

Spraying the plant with glyphosate e.g. Round Up, at the required rate will draw the weed killer deep into the rhizome at a time of year when plant nutrients are naturally retreating back into the rhizome. Repeated sprays in the autumn of each year will bring the plant under check and represents the best means of resolving the problem.

Seek out a specialist, someone who is authorised in pesticide use, management plans can be drawn up and treatment options identified and implemented.

Prevention

Topsoil – be sure of the source of any topsoil you import onto your lands and seek absolute clarification that it is free of Japanese knotweed.

Infested lands in the vicinity of your property should be treated to ensure that your own property does not become affected.

Final advice – local communities should work together to manage the threat. There are affected areas in every townland in North Kerry. Lyreacrompane, Clounmacon, Derra Bog, Bedford, Dromclough are particularly affected. Lyreacrompane has developed a section in its own website on how to deal with Japanese knotweed, see www.lyreacrumpane.com.

Lastly, do not buy any property, land or a development site without first assessing the site for Japanese knotweed.

Corridan & Associates can positively identify the plant; if you require a property survey to rule in or out the plant’s existence call 068 57463/086 8145184.