1 Taking control of Japanese Knotweed

Japanese Knotweed is one of the best known invasive weeds and has been increasingly in the news recently. We look at the latest techniques and control strategies

Japanese KnotweedThe profile of Japanese Knotweed has risen dramatically in the last 10 years, with widely reported cases of problems for developers, householders and amenity managers from this invasive weed.

Part of the challenge, explains Monsanto's technical manager Manda Sansom, is that Japanese Knotweed is very easy to spread and much harder to control.

"Spread is via fragments of roots and stem, (often referred to as propagules), which are transported from the original parent plant either naturally, along rivers and watercourses, or with human assistance, as plant material or as fragments in soil. Pieces of rhizome as small at 1cm can produce new plants and the cut green stems readily regenerate too.

"Japanese Knotweed can colonise most habitats and is able to grow through walls, tarmac and concrete, but it has become infamous mainly due to its spread along watercourses."

"The rhizomes from one plant can be 2m deep and 7m across. In the UK the plant does not produce viable seed, except in the rare instances of hybridisation with other similar introduced species. Many areas of the country have campaigns to eradicate the alien weed and Roundup ProBio and Roundup ProVantage play an important role by controlling the weed with minimum risk to operators, the public and the environment."

David Layland037David Layland, joint managing director of Japanese Knotweed Control Ltd is a member of the steering group of INNSA, a trade body set up to regulate and guarantee the work of invasive weed control contractors. He comments: "Landowners are much more aware of the problem these days, but Japanese Knotweed is so easy to spread from even a tiny fragment of the rhizome and with new developments going up all the time, it is rife."

He adds that mortgage lenders in particular have become more wary of Japanese Knotweed as it can affect the value of a property.

"You need to have a management plan in place because it is not straightforward to eradicate - it can take several years to get the weed under control."

Mr Layland agrees that glyphosate offers the most effective control. "Stem injection trials in the USA looked at a number of active ingredients and glyphosate came out best. It's also the best choice ecologically because it's safe and doesn't leach. Roundup products have evolved over the years and the new formulations travel through the plant much more quickly."

Manda Sansom comments that the control options open to amenity managers have shrunk in recent years. "Since 2013 the approved uses of picloram and high doses of triclopyr for Japanese Knotweed control have been withdrawn.

"A new formulation of aminopyralid and triclopyr, is recommended in certain amenity grassland and industrial situations, but not within one metre of desirable trees or shrubs, on airfields or in forestry, aquatic areas, any land grazed by livestock or where vegetation may be cut for animal feed, bedding, composting or mulching or for sowing any seed within one year of treatment."

Methods of control

Chemical control in aquatic areas needs Environment Agency approval - amenity managers will need to fill in form AqHerb0 1 and submit it to the local EA office.

Clearing the previous year's growth during the winter evens up the new stems and makes spraying easier.

Treated plants take up to six weeks to show symptoms and plant material should only be removed when there is no further sprouting. Re-spraying should only be carried out if there are no visible signs of dieback after six weeks.

As with most broad-leaved perennials, optimum control will be achieved from treatment from flowering in August or September but before die-back.

Sports ground WrexhamTreatment late in the season is the most effective because the glyphosate is transported deep down into the underground rhizome structure along the natural flow of plant nutrients down for winter storage. Japanese Knotweed is sensitive to frost so late season applications should be made in advance of the first frosts.

Treatment in early season is usually less effective because the plant is naturally pushing nutrients strongly upwards to the developing canes. This can lead to a good initial top kill of leaves but less transport to the rhizomes. Regrowth after early season treatment can often be 'epinastic' ie stunted and distorted and because it is not actively growing it is more difficult to kill.

For established stands it is important to plan an effective management programme over several years as repeat applications may well be necessary, either to control very large plants, with their associated underground mass of rhizomes, or to control those plants which were missed by earlier applications due to shading. Sites should be monitored for at least three years.


1) Foliar spray at flowering
This is the optimum timing. Apply the appropriate rate in 200 litres water. Use of specialist extending hand lances is recommended where plants are 2-3m tall. Spray the underside as well as the upper surface of the leaves.

2) Two foliar sprays at 1 metre stem height
Spray the plants at 1-1.5m tall, in late May, with the appropriate rate and repeat on any re-growth later in the season once they reach 1.5m again. This technique can be used where stands are particularly thick, as part of an integrated control programme or where long lances are not available, but will not give as good long term control as spraying at flowering. Re-growth can be stunted and unresponsive to Roundup for a further season.

3) Weedwiper
Applications using a hand held weed wiper have proved successful. Use Roundup ProBio at a 1:2, or Roundup ProVantage at a 1:3 ratio with water. This method can be useful where treatment of nearby vegetation is to be avoided or for spot treatment of small re-growth. It as very high success rates, but it is labour intensive.

4) Stem filling
In certain situations such as when the Japanese Knotweed is growing on sites with a ground flora considered of particular value, or in a garden situation where the Knotweed is growing close to other plants, a stem filling technique may prove a suitable alternative. Although requiring a far higher labour input, the herbicide can be more accurately directed. This technique involves cutting the stem and introducing 10ml of a dilute solution directly through the top. It has been developed by the National Trust, in conjunction with the Cornwall Japanese Knotweed Forum.

5) Stem injection
Use of a stem injection gun can be especially useful for treating small stands, new invasions and to tidy up escapes from eradication control programmes. It is particularly useful where plants are growing intimately with desirable plants or near water.
The tools use a needle to inject Roundup directly into the stem. The original JK1000 Injection System originated in the US and is now available in the UK.
Note: City and Guilds qualification in safe application of pesticides using pedestrian hand held equipment is required. Since February 2015 the relevant module is PA6 021654- 156 (Operating hand held injection equipment).

David Layland comments: "Stem injection is species specific and has a 96 per cent success rate. It's more effective on Japanese Knotweed than spraying which may need 2-3 or even five years of applications to suppress growth. You can also work in all weathers."

Maintaining standards

David Layland cautions that changes to legislation on control of invasive weeds can mean that treatment on a boundary fence requires a warranty to safeguard the neighbouring property. . "A contractor who is a member of a trade body such as the Invasive Non-Native Species Association (INNSA) can provide such a warranty."

Citing the example of 'cowboy' contractors who provide a one-off spray programme purporting to control Japanese Knotweed Mr Layland explains: "INNSA was set up to provide minimum standards in the industry and to ensure that customers are offered bona fide contractors. It can also provide guarantees that the work will be completed in the event of a contractor going out of business."

Registration with INNSA provides members with a recognised accreditation supported by a comprehensive insurance backed guarantee scheme, but only after companies have gone through a strict application process.

New members seeking to join from within the treatment industry, as well as consultants and suppliers to the trade, are required to be BASIS-qualified and accredited to ISO 9000 and ISO 14001, as well as subject to strict financial checks during an annual audit.

Using the Environment Agency Code of Practice as a base mark for the services provided, INNSA members will work within a framework of standards, designed to ensure customers are offered the right product and that the right service is delivered.

INNSA works closely with conveyancers, estate agents, health and safety consultants and government regulators to help shape treatment strategy and can advise on how legislation affects individual landowners. INNSA's quality control has also been further reinforced recently with the launch of the new INNS Code of Practice.

The Code builds on the technical standards that INNSA requires of its members and the established criteria that new members wishing to join the Association must adhere to. It is designed to ensure that members are completely transparent in specifying the services they offer and the costs they charge for remediating sites. It also requires that insurance-backed warranties are put in place, which provide peace of mind to customers once the work has been undertaken.

For details of INNSA visit: www.innsa.org or email join@innsa.org.

The plant

Japanese Knotweed, (Fallopia japonica) was introduced to the UK in 1825 and widely planted as an exotic garden ornamental before the invasive nature of the plant became clear. Japanese Knotweed is probably the most invasive plant in Britain and is scheduled under the 1981 Wildlife and Countryside Act so that it is an offence to plant or cause it to grow in the wild. In addition under the Environment Protection Act (1990) Japanese Knotweed is classified as 'Controlled waste' and must be disposed of at a licensed landfill site in accordance with the Environment Protection Act (Duty of Care) Regulations 1991.

Fleshy, red shoots appear in the early spring from an extensive underground network of stems (rhizomes). The shoots can reach 1.5m by May and 3m by June.

Long racemes of cream flowers appear in late summer and dieback occurs at the first frost of the autumn, leaving the leafless stems to remain throughout the winter.

Dose rates and timing


Dose rate


Overall foliar spray

Roundup ProBio: 5 l/ha or 25ml per litre of water in a standard knapsack sprayer fitted with 200l output nozzles.

Roundup ProVantage 3.75 l/ha or 19ml per litre of water in a standard knapsack sprayer fitted with 200l

output nozzles.

(Spot-treated leaves should be covered in spray droplets but not running off.)

1) Apply to flowering stems from late summer, using long lances 2) Apply late May with a follow-up treatment to healthy regrowth at 1-1.5m height before the first frost.

Hand held weed-wiper *

1 part Roundup ProBio to 2 parts water

1 part Roundup ProVantage to 3 parts water

Stems can be wiped from 1m-3m height in late summer.

Stem filling technique

1 part Roundup ProBio to 4 parts water, 10 ml per stem 1 part Roundup ProVantage to 5.6 parts water, 10 ml per stem

Shortly before senescence from September through October.

Use approved methodology.

Stem Injection with proprietary injection equipment

Either neat product at 2mls per stem or 10 ml per stem of 20% solution made from 1 part Roundup ProBio to 4 parts water.

Either neat product at 1.5 mls per stem or 10ml per stem of 15% solution made from

1 part Roundup ProVantage to 5.6 parts water.

Apply to flowering stems from late summer through October for best results.

Case Study

For many golf club officials and greenkeepers, Japanese Knotweed's prowess as a prolific and resilient invasive plant is well documented and the complexity of the plant, which reproduces and grows quickly and strongly through its underground rhizome and root structure, can indeed cause major problems. These can be compounded at a golf club, where human activity on the playing area has the potential to accelerate its spread to other parts of the course.

Just as common are frequent horror stories about exorbitant treatment costs and, with the golf club sector feeling the economic pinch as much as any business, bringing in external treatment specialists can often fall well down their list of budgetary priorities.
Left unchecked, knotweed can indeed be a 'ticking timebomb' but potentially worse still could be a greenkeeper's decision to carry out their own random spraying, mowing or chopping down, all of which could exacerbate regrowth and spread.

Japanese Knotweed can be effectively managed in a controlled manner, and without prohibitive costs, providing there is early identification and pro-active protection of the affected site and the treatment work is carried out by a competent professional specialist.

Japanese Knotweed Control Ltd's (JKC) David Layland comments: "Our own preferred technique for treating Japanese Knotweed is stem injection, which involves delivery of a measured dose of herbicide into the centre of the plant rather than just the surface. Whatever the chosen treatment, our golden rule for golf clubs would be to appoint a responsible, and competent specialist, only after you have checked the company's industry accreditations, legislative compliance and, if possible, sourced positive customer testimonials and recommendations from previous customers.

Royal Mid SurreyRoyal Mid-Surrey Golf Club is one example of a leading club that took just such an approach. Founded over 100 years ago and comprising two 18 hole courses, it sits idyllically in royal parkland at Richmond upon Thames, adjacent to Kew Gardens.
Here the greenkeepers were battling a major knotweed infestation which had started to spread into the course itself, specifically on two large problem areas; a car park that bordered the 18th fairway and a new proposed teeing ground on the 9th.

General manager Mike Newey and course manager Gavin Kinsella recognised that, if left untreated, the knotweed's continued encroachment on the course could escalate into a major costly issue for the club. Its location next to Kew Gardens presented another challenge. Traditional chemical spraying of large infested areas was not an environmentally acceptable option, whereas Japanese Knotweed Control's localised stem injection method offered a more accurate and efficient solution.

Gavin Kinsella commented: "JKC offered a first class service, impressing us with the efficiency and accuracy of its stem injection system. We were able to see immediate results as the knotweed began to die back and the main benefit has been that no other vegetation or animal life on course, or in the surrounding area including Kew Gardens, has been affected by the treatment."

"The JKC team was professional, personable and highly knowledgeable about the treatment and quickly overcame a problem that threatened to become a major and expensive issue for our golf club."

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