Guest Blog – Japanese Knotweed…

Patrick Horsley on Japanese Knotweed and demolition’s role in its eradication.

Japanese Knotweed (Fallopia Japonica) is the most pernicious invasive weed in the UK. It roots up to three metres deep, can regenerate from plant fragments, and is easily spread in soil, garden waste or even vehicle tyres. It is rapid growing and easily identifiable. Japanese Knotweed has hollow, upright, bamboo like stems, growing up to three metres in height. The large smooth edged leaves range from heart shaped (Japanese Knotweed) to huge “elephant ear” type leaves (Giant Knotweed).

The Seasons of Japanese Knotweed
In the Spring it emerges as a young red/purple shoot that turn green as they age. Some plants can leaf quite early but it can initially grow up to 50 cm as a straight rod. In the summer the plant grows into bamboo like hallow stems up to 4 cm in diameter with very lush, green leaves. In the autumn the plant becomes very attractive as it blooms with long clusters of small green and white flowers. In the winter the stems turn brittle and brown with the now brown and yellow leaves usually falling off at the first frost.

In a built up environment Japanese Knotweed shoots are able to push up through asphalt, damaging pavements, car parks and public utilities. Rhizomes have been recorded penetrating foundations, walls and land drainage.

Japanese Knotweed was introduced to the UK by the Victorians as an ornamental and fodder plant. Due to its root mass, it was used for both bank stabilisation of canals, road verges and railway embankments. The plant spreads from rhizome and stem materials with as little as 10mm length of 0.7g fresh weight of rhizome can give rise to new plants. The crown and the rhizomes act as a massive storage organ which allows massive rapid growth in the spring and is a big advantage for Knotweed over other indigenous plants.

It is an offense to knowingly spread Japanese Knotweed and in a built environment is usually conditioned as part of the planning process for action. Back in 2005 there was a published estimate of circa £1.6 billion to completely eradicate knotweed from the UK’ that figure is probably much higher now.

As a leading business for the eradication of Japanese Knotweed, we are aware of the demolition and construction industry requirements to successfully treat Knotweed at a rate that is compatible with programme constraints throughout the year, including the dormant winter period. The professionals involved with the built environment hold knowledge that there are a few market options to treat and kill Japanese Knotweed in a single growing season, including our own F.A.S.T (Foliage and Stem Treatment) System which is now established, and such herbicidal treatments are clearly the most economic to the end user.

The Government emphasis and intent to reduce carbon footprint has had a severe impact on the cost to remove the problem by way of excavation and transport to tip. The tax levied by HM Customs and Excise is now prohibitive and the ability to apply for contaminated landfill tax exemption has ceased. To offset this penalty, Japanese Knotweed was included in the 2009 Finance Bill for 150% tax relief against the cost of treatment only, but there are exceptions and not all sectors can realise the benefit. It is easy to understand the Government policy, we cannot indefinitely create massive landfill sites simply moving the problem from point A to point B. The number of landfill sites capable of receiving Japanese Knotweed is reducing and the distance to travel from source to tip involves unnecessary lorry movements, sometimes at excessive distances. Using Environment Agency guidelines, a single stand of Japanese Knotweed calculates out at up to 18 lorry transport movements.

The demolition and construction industries need to understand that forward thinking and planning is needed. In the majority of instances Japanese Knotweed is recognised at an early stage and it is now common to see it noted on intrusive site investigation reports as an integral part of the planning process.

The simple rules are that any development that permits a program for eradication in a full growing season can have the plants killed at a cost circa 10% of the cost to tip. Any development that requires immediate excavation and removal to tip will suffer severe and unnecessary financial penalty.

Alternative Solutions?
Industry is not slow to spot an opportunity and a few innovative ideas are now offered
• On site cell burial is available; in our view it is expensive, you need space and you need an area not designated for future development
• There are root barriers available which are designed to stop the spread and will eradicate the plant in the longer term.
• In the last few years, screening out the rhizomes has been introduced
• We have observed a number of market options to design alternative treatments which do not delay development program. These options, which include rapid insitu treatment, have minimal risk and can be conducted at around 25% of the cost to tip

Japanese Knotweed needs professional respect if you want to avoid re-growth and guarantee your actions.

After extensive research, methods have been developed for neutralising the growth of Japanese Knotweed within the soils matrix. The writer has been involved with various treatment protocols for over 16 years. Observations have shown results which have led to develop rapid integrated treatment. Japanese Knotweed rhizomes will not propagate easily when below a certain length and diameter; with the correct dosages of approved herbicide formulae applied directly onto the rhizome, growth can be neutralised.

The solution which allows treatment even in the winter months combines an understanding of the plant physiology with experience on historical eradication.

In simple terms a controlled excavation of the impacted area takes place to remove the plants and rhizomes. The excavated material is transferred into the treatment plant to reduce the rhizome mass to a none viable re-growth size with a simultaneous application of approved herbicide during the treatment cycle. The treated material is set aside or can be returned to the previously excavated pit.

This is just one example of forward thinking being applied. There is no doubt that invasive weed specialists will continue to field test innovative ideas to eradicate the problem within acceptable timescales in the ensuing years but with purposeful forward planning there are products and services available now and which work.

This guest blog was written by Patrick Horsley, director, Invasive Vegetation Management & Treatment Ltd
www.knotweed-uk.com