Spraying invasive plants with herbicide


Treating invasive plants with herbicide can be a very effective method of treatment. You will have to respray. It usually takes at least three years to treat Japanese knotweed. Giant hogweed seeds can continue germinating for 15 years after the last seed fall.

In Northern Ireland

There is no requirement to notify or have agreement/approval from NIEA to use an approved herbicide near a watercourse, unless you are working on a designated water body, when you would require ‘consent’ from the Conservation Designation and Protection unit.

In Scotland

If the invasive plant is near to water, i.e. within 1 metre of the top of the bank, you can apply herbicides under a general binding rule (GBR 23g). So long as you comply with the requirements of the GBR you do not need to contact SEPA. A CAR authorisation will be required for plants growing next to watercourses that are not invasive non-native plants, and for applying herbicides directly to the water (eg treating submerged plants.

The herbicide's effectiveness depends on the type used. An advisor certified by BASIS (the registration, standards and certification scheme for pesticides and fertilisers) will be able to advise you on the most suitable type of herbicide for your situation and when best to apply it.

BASIS: Pesticide and fertiliser registration, standards and certification

Giant hogweed and Himalayan balsam both drop large quantities of seeds. A control programme will need to continue for several years, with checks carried out throughout the growing season. If you are trying to eradicate these plants from a riverbank it is important to ensure that any plants upstream are also treated to avoid seeds being washed onto the site.

Japanese knotweed has a large underground network of rhizomes (underground root-like stems). To eradicate the plant you must kill the rhizomes. Picking the right herbicide is essential, as it must travel through the plant and into the rhizome system below. Several herbicides can treat Japanese knotweed successfully - you will need to pick the right herbicide for your situation. Glyphosate is effective because it penetrates through the whole plant.

Using herbicides

The person doing the spraying must hold a certificate of technical competence for herbicide use or work under the direct supervision of a certificate holder. If you plan to spray in or near water, the person carrying out or supervising the spraying must have the appropriate aquatic part of the qualification. The sprayer must also comply with the pesticide product label and meet all of its conditions. Before you spray in or near water you must check that the product is approved for use near water.

Health and Safety (HSE): Pesticides Register of UK Authorised Products

You can get a certificate of technical competence by attending a short course at an agricultural college or similar institution.

For herbicide to be effective, make sure you use it at the correct time of year:

  • Japanese knotweed is best sprayed in late summer from flowering onwards.
  • Giant hogweed should be sprayed in April or May, before the plants flower, with a second spraying later to avoid any flowering.
  • Himalayan balsam can be sprayed in spring before flowering, then every four weeks until the first frosts; but, strimming or hand pulling should be your preferred option for control of this plant.

You must follow the guidance in the statutory code of practice for plant protection products. If you follow its advice you should stay within the law.

You must make sure that your pesticide application equipment is tested when five years old. Rucksacks and handheld sprayers are exempt. From 26 November 2015 Grandfather Rights expired (they may have applied if you spray on your own or your employers land) and pesticide spraying must always be carried out by someone with the appropriate certificate.

Working near water

If the invasive plants are near a watercourse, consideration should be given to mechanical removal methods, where possible. See the Cutting and burning invasive plants page.

In Northern Ireland, There is no requirement to notify or have agreement/approval from NIEA to use an approved herbicide near a watercourse, unless you are working on a designated water body, when you would require ‘consent’ from the Conservation Designation and Protection unit.

In Scotland, If you are planning to use herbicide in or near to a watercourse, you must consult SEPA. You can apply herbicide to an invasive non-native plant, growing within 1 metre of the top of the bank, without contacting SEPA as long as you follow the rules set out in GBR 23g.

You must also carry out a Control of Substances Hazardous to Health (COSHH) assessment for any activities that involve herbicides.

Dispose of waste herbicides correctly

You must make sure that all your waste is stored, transported and disposed of safely. Waste herbicides are likely to be classed as hazardous/special waste. You must keep this separate from other waste.

Herbicide containers must either be rinsed or handled as herbicides. Check product labels to see if your waste containers should be rinsed. Water used for rinsing empty containers is classed as dilute pesticides or biocides.

In Northern Ireland, you may need a groundwater authorisation, registered waste exemption or trade effluent consent to dispose of water used for rinsing empty containers.

In Scotland you may need an authorisation or permission to dispose of water used for rinsing empty containers. Contact SEPA for further information.

Pesticides and Biocides

Further information

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