Japanese Knotweed Survey
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Japanese Knotweed Survey

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Japanese Knotweed Herbicide Treatment Product Options  

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This information is not designed to be specific but to raise awareness of what you need to consider and be aware of before using herbicides. The use of herbicides is often the most effective option for the control of Japanese knotweed but there are issues that need to be considered first. The main issue is whether the stand is near water or not. Consent is required from the Environment Agency if herbicides are to be sprayed near water and only two products are approved (see below). There are health and safety issues and those administering herbicide need to be properly trained and hold a Certificate of Competence.

In the UK it is a legal requirement for people who are spraying with professional pesticides to hold an NPTC pesticides certificate of competence, otherwise known as a spraying certificate or a pesticide license. Courses are offered to assist someone to pass an NPTC assessment so that they can safely and legally use pesticides application equipment. Herbicides should only be used in accordance with the advice on the label otherwise it is considered an offence. It is also an offence to use products that are not approved. Check that the herbicide formulation is approved for the intended use. Furthermore there is an obligation to avoid the spread of herbicide to non-target areas so spraying needs to be carried out in dry weather. Spraying should also be carried out in wind speeds below Force 2 on the Beaufort scale to avoid spray drift.

Japanese knotweed can become very tall which makes it difficult to apply herbicides. The plants should ideally be sprayed in the spring when they are about 1m tall or after cutting when they have re-grown to this height. There are various methods of application including tractor-mounted spraying for large areas; knapsack spraying for small areas; lance sprayer for tall stands or for stands in inaccessible places (such as steep slopes and river banks); controlled droplet applicaton; injection method for small stands and weed wiper or herbicide gloves for direct application onto leaves of specific plants.

Dense stands of Japanese knotweed can be treated with a Glyphosate-based herbicide, such as 'Roundup pro Biactive'. Glyphosate is a systemic herbicide, which acts by blocking a plant’s enzyme system. The herbicide is absorbed through growing leaves and stems where it is translocated throughout the plant and root network. It kills virtually all annual and perennial weeds including grasses. Glyphosate is quickly broken down in soil or sediment and is harmless to animal life. Not all formulations containing Glyphosate are approved for use in or near watercourses under the Control of Pesticides Regulations 1986.

If the Japanese knotweed is sparsely distributed, use a 2,4-D amine preparation such as Dormone, which is specific to broadleaved plants and will not harm the grasses. It may take two or three years to completely kill the entire plant. More effective control can be achieved if Japanese knotweed is cut or sprayed in early summer, and then sprayed again in late summer, just before the winter dieback.

More targeted methods of applying herbicides are being developed for sites where it is important to protect the native flora. This includes using a weed wiper to apply the herbicide directly to the leaves of the plant rather than spraying or injecting herbicide directly into the plant. This ensures that only target plants are treated.

The plants should be treated between March and October when they are in the growing phase. Plants can take up to 6 weeks to show signs of die-back. There are two main groups of herbicides and the one you choose will depend on the site. The main recommended herbicides are:

For environmentally sensitive habitats and those near water

Glyphosate* e.g. Roundup
2,4-D Amine* e.g. Dormone

For habitats not near water

Picloram e.g. Tordon 22K
Triclopyr e.g. Vitax SBK Brushwood Killer
Imazapyr e.g. Arsenal

* Not all herbicides containing these active ingredients are suitable for use in or near water. Use of herbicides in or near water requires consultation with the Environment Agency.

Glyphosate e.g. Roundup


2, 4-D Amine e.g. Dormone

Picloram e.g. Tordon 22K


Triclopyr e.g. Vitax SBK Brushwood Killer


Imazapyr e.g. Arsenal

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Company’s Registered Office Address: 597 Etruria Rd, Basford, Stoke On Trent, Staffordshire. ST4 6HP.
Japanese Knotweed Survey © Copyright 2011

Japanese knotweed survey, management, control, eradication & land remediation relief.
Areas include Staffordshire, Cheshire, West Midlands, Manchester, Birmingham & Stoke On Trent.

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