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40 things you need to know about Japanese knotweed – Part one

40 things you need to know about Japanese knotweed – Part one


So you’ve discovered Japanese knotweed on your property and want to know what to do next – So you probably went to Google..

Firstly, don’t panic. The internet can be a great source of information. However within the world of Japanese knotweed the online (and offline) information available seems to be particularly aimed at scaremongering.

Yes, Japanese knotweed is a problem (because mortgage companies will initially refuse lending unless a management plan with an insurance backed guarantee is in place) and if left to grow uncontrolled can cause damage to buildings, hard landscaping and your (or even your neighbours) garden.

However, it is not all doom and gloom. Environet are here to help and guide you.

Drawing on our 21 years of experience we are looking to both educate and placate you on all things Japanese knotweed.

Here, in the first blog topic in a regular series, we will be looking at the 40 things we think you need to know about Japanese knotweed. Part one covers points 1-5, with 6-40 to be covered at various times throughout the coming 12 months.

1. Is Japanese knotweed covered under normal household insurance policies?

Most household/buildings insurance policies will not cover liabilities associated with Japanese knotweed, with the possible exception of legal expenses cover where legal claims are made or brought by the insured.

It is possible to buy specific indemnity insurance to cover the risks associated with Japanese knotweed, namely cost of professional treatment, repairs to the property caused by knotweed, legal defence against third party claims resulting from encroachment, and for proven diminution (i.e. reduction) in value to the insured property.

2. What removal methods are available? 

Herbicide treatments – Herbicide treatment is a popular control method, carried out during the growing season. Treatment control programmes usually consist of 4 treatments, spread over 2 growing seasons with a monitoring visit in year 3. It has the benefit of being low cost, but should be considered as a “control” (as opposed to an “eradication” or “removal”) method.

Physical removal – Physically removing the root system has a far better chance of achieving complete eradication. Environet’s Resi-Dig-Out™ method has been developed for residential properties using the same concept as their patented Xtract™ method for commercial sites. Knotweed infested soil is excavated and the viable rhizome is separated and removed from the soil. It can be completed in a matter of days, at any time of the year, and comes with insurance backed guarantees for up to 10 years.

3. If you are planning to build or hard-landscape over an affected area does this alter the method of treatment that should be used?

If you are planning to build or hard-landscape in an area affected by Japanese knotweed it is strongly recommended that you do not rely solely on a herbicide method. Herbicide treatment can kill the entire rhizome system, but it is far more likely that the chemical simply induces temporary dormancy. The lack of any visible growth gives the false expectation that the knotweed is dead, which sadly is not normally the case. When the ground is subsequently disturbed regrowth occurs, causing expensive construction delays, increased removal costs, and the prospect of your new building or hard-landscaping being damaged by knotweed in the future. For these reasons we recommend a physical removal method such Resi-Dig-Out™ or Xtract™.

4. What’s the difference between an Insurance Backed Guarantee (IBG) underwritten by a rated insurer and other IBGs?

The primary difference is the security a world-class insurer provides. Most IBGs provided by other Japanese knotweed specialists are backed by non-rated insurers. The insurer that underwrites Environet guarantees is “AA-” rated.

If you are considering another Japanese knotweed specialist we urge you to obtain a sample copy of the IBG to check it provides the cover you need. In particular look at the limit of liability, when the insurance element of the guarantee kicks in, and what you need to do, and pay, to make a claim. You might be surprised to learn that the limit of liability is low, the insurance element does not come into force for some 4-5 years after treatment commences, and that you might have to pay to make a claim.

5. What’s the problem with Japanese knotweed growing on residential property?

The problems that Japanese knotweed creates are well documented. The primary concern is its ability to grow through anything in its way, damaging buildings, driveways, patios, boundary walls, and drainage systems to name but a few.

As a result all the major banks and building societies have strict lending criteria on knotweed affected properties, which can make obtaining mortgages more difficult and more expensive. Consequently the presence of Japanese knotweed on a residential property is likely to reduce the property’s value.

This has increased the awareness of the Japanese knotweed problem and lead to a rising number of legal disputes particularly between owners of neighbouring land, where knotweed has encroached (i.e. spread) from one property to another.

40 things you need to know about Japanese knotweed – Part two – Points 6-10 coming soon.

In the meantime our team of experts are on hand to answer any questions you may have. Call us today on 01932 868 700 and we’ll be happy to help. 

Robert Spaceman

“We had a large stand of bamboo removed, thinned, contained and replaced. The customer service has been first class. Joe and Jason were fabulous and kept me well informed at all times”.