Japanese Knotweed is a highly invasive plant that can seriously damage buildings, roads and pavements. Such damage, caused by the plant’s rapidly growing roots and stems, is estimated to cost the UK economy over £166 million per year in treatment costs and property devaluations.

Japanese Knotweed, more formally referred to as Fallopia Japonica, was first brought to Europe in the 1840s by German botanist Phillipp von Siebold who found the plant growing on the side of a Japanese volcano. By 1850 the Royal Botanic Gardens in Kew had received their first shipment and the plant quickly gained popularity with UK gardeners due to its bamboo-like appearance and ability to grow almost anywhere. The plant also began to be used by farmers as feed for their animals.

Over the years the plant gained a notorious reputation for an ability to ‘escape’ and grow in the wild. Japanese Knotweed’s extensive root system and ability to grow up to 20cm per day and swamp all surrounding plants soon made it more than just a mild nuisance. In more recent years increasing awareness of the plant’s impressive ability to grow through concrete and tarmac has made its presence a serious turn off for property purchasers and mortgage lenders alike. Such is the government’s concern about the spread of Japanese Knotweed that if you are found to be failing to adequately control the plant (or other invasive species such as Himalayan Balsam and Giant Hogweed), you can be issued an Antisocial Behaviour Order and fine up to £2,500.

When selling your property it is vital that you correctly complete the TA6 Property Information Form. The form raises an enquiry as to whether the property is affected by the plant and allows for the responses of ‘yes’, ‘no’ or ‘don’t know’. A response of ‘no’ is a statement of fact and would allow the buyer to take action against you if the weed is in fact present. A response of ‘don’t know’ may be considered a representation that attempts have been made to investigate. If you are unsure about the presence of Japanese Knotweed at your property, our suggestion is to make it clear that there has been no attempt to find out. Please be mindful that, due to the rate at which it spreads, Japanese Knotweed may well be present in your neighbourhood. Sellers of Commercial property should also be aware that the presence of Japanese Knotweed is also required in response to the Commercial Property Standard Enquiries as it constitutes a contaminated substance and an infestation.

How big is the problem?

A 1998 survey showed that Japanese Knotweed covered an area of nearly 100 hectares in Swansea alone. A DEFRA review has stated that a UK wide programme of eradication would cost in the region of £1.5 billion.

How do I know if I have got Japanese Knotweed?

DEFRA describes the plant as appearing in dense clumps and comprising of:

– fleshy red tinged shoots when if first breaks through the ground
– large, heart or spade shaped leaves arranged in a zig-zag pattern along the stem
– hollow stems resembling bamboo
– clusters of cream-white flowers towards the end of July that attract bees

How to tackle Japanese Knotweed

Japanese Knotweed is very difficult to eliminate effectively and options include:

– Digging it up – although this is the most obvious method of eradicating the weed, it must be remembered that roots that can grow up to 3 metre deep and it takes just 0.8g of root for a new plant to grow. The weed is also classed as ‘controlled waste’ under the Environmental Protection Act 1990 and can only be disposed of at licensed landfill sites.
– Chemicals – treatments containing glyphosate are effective but it may take several years to completely eradicate the plant. Please visit the Royal Horticultural Society website on the following link for more details on the chemicals available and how best to apply them https://www.rhs.org.uk/advice/profile?pid=218

Good News for the Future

In 2010 scientists introduced several colonies of Aphlara Itadori, a Japanese insect, to the UK that feeds almost exclusively on Japanese Knotweed. If these colonies can successfully adapt to our climate in significant numbers, then it is hoped they will present a more natural control on the spread of Japanese Knotweed.