Taming the Giant

Controlling Giant Hogweed

Safety First

When controlling giant hogweed (or working near it) always wear gloves, cover arms and legs, and ideally wear a face mask. All giant hogweed waste/debris, contaminated clothing and tools are potential hazards.

Wash immediately any affected area (eyes or skin), keep affected skin away from light sources and seek medical help immediately.

The owner of any affected land should erect fencing to stop people coming into contact with the weed, along with appropriate warning signs.

On giant hogweed impacted building sites or developments it is advisable to inform first-aiders and have appropriate wash facilities, protective clothing and procedures in place to deal with eventualities that could arise as a result of the infestation. Ensure that contractors are aware of the risks and that steps are taken to protect personnel from harm.

If possible, carry out control measures in overcast weather avoiding sunny periods.

Control objectives methods

There are two main objectives to a giant hogweed control programme. Firstly, any existing plants should be killed with the focus then shifting onto eradicating the seed bank.

PBA offer a targeted giant hogweed control programme which is comprised of three stages.

  1. Preventing seed production and seed dispersal - we safely remove giant hogweed flower heads and seed heads, ensuring that seed spread is prevented.
  2. We control the growth of viable plants by using an appropriate control method such as taproot cutting, hand-pulling and herbicide treatments.
  3. Removal of the seed bank or repeat control of new plant production to prevent flowering and seed production, repeated until the seed bank is exhausted.

Environmentally sound options are preferable. Although sadly not always the most cost-effective or achievable, these options should be first on the list.

Non-chemical controls

On a garden scale, appropriate measures include pulling up young plants by hand when the soil is moist. This is best done in May when the giant hogweed has reached a reasonable height, but before it has produced its flowering spike. For larger plants it might be necessary to loosen the roots with a fork first. For large infestations on more open sites, mechanical pulling might be a better option, achievable with an appropriately sized excavator.

If the flower spike has already formed, remove it before the flowers fade. This is also a good time to trim the plant, as it less likely to survive trimming than earlier in the year. Cutting is always preferable to strimming, for obvious reasons. If strimming is the only available option, make absolutely sure that those carrying out the task wear full protective clothing that is appropriate to the task.

Larger scale areas should really be dealt with by professionals. Manual techniques may not be suitable in these circumstances. Using appropriate machinery, the infestation can be cut, pulled, mulched, dug or stripped out. Control of the growing crowns and seed bank produced by an established infestation may only be achievable using mechanical forms of control, or a long term herbicide application programme.

Chemical controls

Giant hogweed prefers moist fertile areas often near waterways. It is essential that weed-killer is not allowed to enter waterways. Environment Agency permission must be sought and given before undertaking spraying near rivers, streams and ponds.

Controlling the giant hogweed seed bank can be achieved through repetitive herbicide treatments of the live plants prior to seed formation. With this process, four or five years will normally be needed before the seed bank is sufficiently depleted. Consideration has to be given to treating all plants in a location rather than those growing on a single property since seed can be blown in from neighbouring infestations. Systemic weed-killers based on glyphosate are usually the best choice as these kill roots also.

Disposing of giant hogweed

Giant hogweed material is classed as a controlled waste so, if it is taken off site, it can only be disposed of in licensed landfill sites with the required documentation.

Worth knowing…

The smaller, native hogweed, Heracleum sphondylium, is often confused for giant hogweed. Contact with this plant can produce irritation and rashes but not to the same degree as with giant hogweed. Native hogweed waste materials are not classed as controlled waste but should still be disposed of with care to avoid human contact.

How PBA can help...

PBA have many years experience and are accredited to deal with all aspects of giant hogweed management and control. We work with private property owners, estate agents and management, developers and public sector organisations in the remediation of land impacted by giant hogweed and provide Management Plans that enable effective control solutions to be developed and actioned.

For more information, call PBA on 0203 174 2187 or 01202 816134.

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