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Dealing with the problem of Japanese knotweed

Posted 7 November 2017 by Keith Osborne

How can you resolve the problem of Japanese knotweed on your property? We speak to the experts at Environet for their advice on removing it.

Japanese knotweed is one of Britain’s biggest problem plants. It costs the UK £116m a year in treatments and devaluations to homes. It’s illegal to let it spread to neighbouring land and, if you have it somewhere on your property and don’t deal with it properly, it could end up causing serious damage. Getting a mortgage with Japanese knotweed in the garden can be difficult.

Environet is one of Britain’s leading Japanese knotweed eradication firms. In recent years, it has invested heavily in research and development to find ways to effectively eliminate the plant. That has led to pioneering treatments that are now used by homeowners and businesses across the UK.

We spoke to managing director Nic Seal about the scourge of Japanese knotweed and if Britain will ever be free of its ravages.

Let's start off by discussing the scale of the Japanese knotweed problem around the UK. Just how bad, or big, is it?

It's bad – and getting worse. It's bad because it can damage property, can affect the property's mortgageability and can lead to legal disputes between neighbours and between buyers and sellers. We've done some research and reckon around 5% of residential properties are affected by knotweed.

Which parts of the UK are worst affected and why?

It's found pretty much everywhere in the UK — in gardens, on brownfield sites, along rivers, roads, railways, even in graveyards. It's not fussy about where it grows. You'll find it in all parts of the UK, but it's more predominant in areas of high human population due to the fact that man is the main culprit for its spread.

Do you think the government – successive governments over the last couple of decades – have done enough to try and eliminate Japanese knotweed?

A while back the government of the day was saying it would cost upwards of £1.5bn to get rid of it using conventional methods and was even considering introducing an insect to eat it.

I think they have, but then I'm not one for too much government intervention. In my mind, the property owner should be responsible for knotweed treatment. It should not be for the taxpayer to fund treatment programmes from privately owned land. Of course, where legal requirements are in place, it’s important that these are properly enforced. Sadly, that is not always the case, giving the unscrupulous operator a competitive edge.

Is it a problem that is unique to the UK, or are other countries in Europe similarly affected?

It's found in other European countries, particularly in the north. The problem is recognised as such much more within the UK, probably due to our industrial history, our high land values and population density. I think it would be fair to say that the UK leads the global fight against knotweed.

Many of us know that Japanese knotweed grows like wildfire, but apart from that, what does it do that causes such difficulties for homeowners and indeed businesses?

Japanese knotweed​It’s very difficult to kill, and laughs at DIY, and some attempts by so-called professionals. It can easily damage property. Lenders may refuse mortgages on affected property, which undoubtedly has an effect on value. When values are challenged, the lawyers get involved, resulting in an increase in disputes and litigation between neighbours and buyers and sellers of affected property. It's a particularly big problem on sites where ground is to be disturbed, such as construction and development sites.

Is it at all possible to deal with the problem yourself to successfully eradicate it from a site with no outside help?

Many have tried – no doubt a small percentage has succeeded – but judging by the number of calls we get, the lion’s share fail. Remember that if one intends to sell the property, an insurance-backed guarantee will be required, and it will be difficult to find if a non-professional knotweed company has not been used.

Calling in the pros, like yourselves at Environet – what's it going to cost?

A typical residential property with a five-year insurance-backed guarantee will cost in the region of £2,300 + VAT for herbicide treatment. A physical dig-out will cost at least twice as much. On large commercial development sites, costs can easily rise, but then it’s a smart, and necessary, investment.

Is there a way to remove Japanese knotweed organically?

If by "organically" you mean without chemicals, then yes, there is a way to remove knotweed. It involves physical excavation and removal of all viable rhizome (roots). It's difficult because rhizome can extend many metres from the visible plant and to a depth of at least two metres, possibly more. The rhizome is very brittle and small pieces can regenerate into a new plant. It's the method with the best chance of success and has the advantage that it can be done at any time of the year, taking just a matter of days.

Your company has invested heavily in research and development to find more effective ways to combat Japanese knotweed. What have you discovered?

We've learnt what the plant likes and dislikes; we're getting closer to finding its Achilles heel. We understand its dormancy defence mechanism, which is very successful in fooling people into thinking it’s dead when its not, leading to yet further spread.

Do you think the UK will ever be rid of Japanese knotweed, or even brought under control? And if so, approximately by when?

I don't think it will ever be eradicated from the UK, but I think it will eventually be brought under control as techniques improve and greater resources are expended. When that will happen is anyone's guess, but I'd wager not in my lifetime.

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