SNH provide a good overview to managing Invasive non-native plants for different user groups:http://www.snh.gov.uk/land-and-sea/pests-and-diseases/japanese-knotweed/
Free environmental guidance for small and medium sized businesses is available from NetRegs, which is a partnership between Northern Ireland Environment Agency (NIEA) and SEPA: http://www.netregs.org.uk/environmental-topics/land/japanese-knotweed-giant-hogweed-and-other-invasive-weeds/
It is best to undertake control sooner rather than later, as, if left, it will spread and become more difficult to control. It is not recommended to strim the plant as it can regenerate from the cut fragments which are spread by strimming. The plant also spreads through underground rhizomes, but has not been recorded spreading by seed in the UK. Applying glyphosate based herbicide from late August to October, to maximise uptake into the roots, is an effective method of control, but it can take several years of application to kill the plants. Successfully treated areas should be monitored for a number of years after the apparent removal of the plant, as there have been reports of regrowth many years after plants were apparently dead. Stem injection is proving to be an effective option; although initially more labour intensive, results have shown it to be an effective method of killing plants and the method ensures that only target plants are treated, thus reducing impacts on the native flora. The use of ‘weed wipes’ also allow a more targeted application.
Glyphosate is the only herbicide that is effective on Japanese knotweed that is also approved for use near a watercourse. However, a licence is required for spraying near a watercourse, so the Environmental Protection team at your local SEPA office should be consulted:
Japanese Knotweed - Homeowner Issues (mortgages and guarantees)
If you are concerned about the potential impact of Japanese knotweed on your property, in certain circumstances it may be appropriate to contact a professional weed control company who will treat Japanese knotweed for you. It may be preferable to choose one that provides an Insurance Backed Guarantee for Japanese Knotweed control around your home and garden, similar to that for treatment of woodworm or dry rot inside your house. Many mortgage lenders now accept these guarantees. Further useful advice for householders is provided by the Property Care Association (PCA):
For more detail, the PCA Japanese Knotweed Code of Practice (especially Chapters 16-19) provides advice on reports and warranties for control in areas adjacent to properties:
Information about Insurance Backed Guarantees can be found at: http://www.property-care.org/Homeowners.GPI.asp
Protective clothing must be worn when attemping control. Strimming or composting is NOT recommended.
The best time for control work with herbicides is in spring when the plants have reached a height of 20 – 50 cm and have not set seed. The low height of the plant will also allow access to the centre of stands. Follow-up spraying should be carried out to treat seedlings which have germinated after the first treatment. Everytime you spray you need to spray both the top and underside of the leaves. Long-lance sprayers may improve accuracy of application. Glyphosate can be applied as a spot treatment to individual plants, using hand-held equipment. Again, a licence from SEPA is required if you wish to spray near water: https://www.sepa.org.uk/contact/
Ideally, control work should aim to prevent the plant producing flower heads. Cutting the flower head off is not recommended as it will only encourage secondary flower spikes. Cutting at the base of the plant can be effective, but is also not recommended as the sap can cause burns to the skin. If the plant does manage to flower, the best advice is to reduce the seed fall by tying a plastic bag over any flower heads.
This is an annual plant which grows each year from the previous year’s seeds, so the aim of control is to prevent the plant from flowering and setting seed. Scattered plants are best pulled by hand, being careful to remove the whole plant. Cutting or grazing on dense stands can also achieve control but cutting should not be attempted once the seed heads have formed, as this would effectively spread the plant. Continual monitoring should be undertaken to prevent reseeding as cut plants can regrow. The first monitoring visit should be timed shortly after cutting, as Himalayan Balsam has been known to re-grow within weeks of control.
Chemical control can be used for high density large populations but the use of herbicides near a watercourse is restricted and requires prior written permission from SEPA. Chemical control can take up to two years to eradicate the plant (with additional monitoring following this). Initial treatment should be carried out from May to early July, with follow-up visits to remove any late flowers (and prevent seeding). This work should be ongoing until the first frost of autumn.
It may also be necessary to consider a bankside rehabilitation programme to prevent erosion, once the plants have been removed.
Carrying Out Control
It is an offence to spray on land you do not own without the landowner’s permission. The Registers of Scotland https://www.ros.gov.uk/home can be consulted for information on who owns an area of land, but they do charge a fee.
Spraying Certificate - Anyone spraying outwith a domestic garden requires a spraying certificate of competence; in this case a PA1 / PA6a certificate. Anyone who previously used pesticides under ‘grandfather rights’ will need to do their PA1/ PA6 , as they have been revoked since November 2015.
For domestic use, The Health and Safety Executive (HSE): http://www.pesticides.gov.uk/guidance/industries/pesticides/user-areas/garden-home has advice on which pesticides can be used; you can use their ‘garden search form’, with ‘glyphosate’ entered as the active ingredient, to establish which pesticides are suitable.
INNS as Controlled Waste
Waste material containing some invasive non-native species, such as giant hogweed and Japanese knotweed, is classed as “controlled waste” and as such must be handled, transported and disposed of appropriately, as covered by the Environment Protection Act 1990: http://www.netregs.org.uk/legislation/scotland/current/waste_legislation.aspx
The SEPA waste team can provide advice on controlled waste procedures and the Environment Protection Act 1990: https://www.sepa.org.uk/contact/
SEPA also provide guidance on how INNS should be managed on construction sites: