Giant hogweed

The options

Landowners frequently ask: why can't I just cut it down? This method of treatment should be avoided for the following reasons:

• the health and safety of the persons involved in cutting it down;
• the long-term viability of Giant hogweed seeds; and
• cutting leaves the root intact and increases the probability that the plant will simply regrow.

The most important reason is the health of the persons involved in cutting it down (see health risks to humans). Stringent procedures need to be followed by anyone coming into contact with the plant because of the health risks. The sheer size of the plant increases these risks (see dos and don'ts). Fallen or cut stems will still be hazardous until all the sap within them has completely dried out.

Giant hogweed seeds remain viable for a long time so consider the effects of this too. Once the plant has produced stems and flower heads, preventing seed production can prove difficult. Cutting down the stems of a Giant hogweed plant in flower can result in new flower heads developing from the nearest stem junction below the cut - so there will still be thousands of seeds to deal with.

If cutting down Giant hogweed is unavoidable, consider the following when determining at what time of year the work should take place.

• Ideally, carry out treatment early in the season before the plant produces any stems (before early to mid-summer).
• Avoid cutting down fully-grown stems to reduce the health risks to the persons involved in cutting it down.
• Carry out treatment before the plant produces any more seeds.

Treatment methods

Herbicide control

Herbicide control is the most common treatment method, with glyphosate being the most popular herbicide used. It is best conducted in the spring, where a couple of treatments 3 or 4 weeks apart can be all that's needed to kill off the plant. It is better to treat the plant before it produces new seeds. Seeds that have already been released in previous years and have not yet germinated (the so-called 'seed bank') must be factored into any treatment programme, as these seeds can take years before they emerge as new plants. In this situation, implement a system of annual monitoring and treatment of seedlings.

Excavation

Giant hogweed can be excavated but disposal of excavated material would need to occur at a licensed landfill facility. Consequently, both in sustainable and financial terms, excavation should probably be regarded as a last resort. Excavation of Giant hogweed plants should include a 4 metre radius around each plant to take into account the seed bank.

Timescales for treatment

Excavation of plants, roots and seed bank can be conducted within no more than a few weeks, depending on the size of the area to be excavated.

A herbicidal treatment programme, if treatment begins early enough (e.g. spring), can eradicate a plant within a couple of months. However, a seed bank monitoring programme should be in place for a minimum of 5 years.