Environmental guidance for your business in Northern Ireland & Scotland
Clearing the leaves and stems of Japanese knotweed or giant hogweed that are above ground and then removing soil contaminated with roots, rhizomes (underground root-like stems) and seeds can provide faster results than just spraying with herbicide.
Try to minimise the amount of waste you generate that contains invasive plants, or their seeds and rhizomes. Any waste you do produce should be treated on site where possible.
Any waste that is taken off site must be taken by a licensed waste carrier and must go to a suitably authorised landfill site.
If you intend to bury invasive plant waste on your property you must contact your environmental regulator to check you are allowed to do this at your location.
See the page in this guideline: Burying invasive plant material on site.
You should not remove soil from river banks, as this can cause water pollution. If you are planning to carry out work near a river you should contact the Northern Ireland Environment Agency (NIEA) or Scottish Environment Protection Agency (SEPA).
If your site floods, the seeds will be spread further across the site, so you will need to manage a larger area.
To clear ground contaminated with giant hogweed, you may need to remove soil up to 4 metres away from the plants and to a depth of 0.5 metres. You will need to check for regrowth regularly. You should spray regrowth with the herbicide glyphosate before the plants flower.
The rhizome system beneath a stand of Japanese knotweed can be over 4 metres deep and could extend for at least 7 metres around the stand. If you are going to dig out the rhizome system you will need to remove all of the plant material. You should use the rhizome identification guide in the knotweed code of practice, or ask a specialist, to help you identify the plant material.
You will need to check any cleared areas regularly for regrowth. You can spray any regrowth with herbicide.
To clear ground contaminated with Himalayan balsam, you may need to remove soil up to 6 metres from the parent plant and to a depth of 0.5 metres. You should not remove soil while the seed pods are present. You will need to check for regrowth regularly. You should pull by hand or strim regrowth before the plants flower.
However, as seeds remain viable in the soil for several years, annual cutting, mowing or grazing or annual herbicide treatment during the spring growing season can be an effective control for this plant. You must also carry out follow up checks for late germinating seeds.
Never stockpile contaminated soil or plant material within 10 metres of a watercourse or within 7 metres of your site boundary.
Collect any water you use for cleaning vehicles that are used in contaminated areas. If it is contaminated with seeds or plant material, you must not discharge it to a watercourse. You could treat the water by passing it through a settlement tank to remove any soil before passing it through a very fine mesh sieve to remove seeds or plant material. Settlement alone may not be adequate because seeds and plant material float.
You may be able to deposit material sieved from water used for vehicle washing in a controlled area on your land and monitor it for regrowth. You should speak to the NIEA or SEPA to determine your best option.
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