Giant Hogweed (Heracleum mantegazzianum) is a large plant, growing up to five metres tall.  Introduced as an ornamental, it was first recorded wild in the UK in the late 19th century.Giant hogweed spreads solely by seeds, mainly through deliberate planting, wind dispersal and in water courses. It is now common across much of the UK.

Contact with any part of this plant must be avoided as even minute amounts of sap can cause blistering of the skin following exposure to sunlight.

Other negative impacts include out-competing native flora, river bank erosion and increasing flood risks.

Non-chemical control

Cutting

Cut stem below ground using an axe or spade. Cut regularly early in the season to prevent flowering. Cutting should be repeated regularly for between 5 and 10 years to eradicate the plant.

Digging

Shallow excavation to about 20cm will remove the growing crown. This can be done with an axe or sharp spade. Spoil should be disposed of at landfill or by piling on site and composting. Any regrowth should be treated chemically.

Grazing

Grazing by cattle, sheep, pigs or goats throughout the growing season will suppress growth, but does not eradicate it.

Chemical control

Herbicides

Using glyphosate at 6 litres/ha is the most effective method. Spraying can start as soon as the plant is about 1m high, usually in March and continue throughout the summer. More than one application is often necessary and follow-up spraying will be required to kill seedlings in subsequent years.

When mixed with other plants, use a weed wipe when plants are about 1m tall between March and May. When plants are more than 1.5m tall, proceed with extreme caution. Repeat chemical treatment may be required for up to 10 years.

Stem Injection

Cutting the stem above ground, followed by injection of 1 in 10 dilution of glyphosate in water below the first node, will give good control. This technique can be used for established plants later in the season.

It is essential to establish vegetation quickly after control measures have been applied. A dense grass sward is ideal as it tends to discourage seed germination.

Control should be undertaken on a catchment basis, working from the upstream end to prevent seed spread.

For more information on how to identify and control Giant Hogweed please visit the GB Non-Native Species Scretariat webpage here.