Giant hogweed
Botanical Name
Heracleum mantegazzianum
Family
Apiaceae (carrot)
Also known as
Wild rhubarb, cartwheel flower, wild parsnip
Where is it originally from?
South West Asia / Eurasia
What does it look like?
Massive, erect, biennial herb (<6 m) growing from a forked or branched taproot with large leaves (50-100 cm long), made up of three bristled, deeply divided leaflets, forming a rosette at the base. Grooved, hollow stems (5-10 cm diameter) are blotched and spotted reddish purple, and have sturdy bristles containing a toxic sap. From December to February in its second year it produces a tall flower stalk with leaves attached and large umbrella-like clusters (20-60 cm diameter) of white flowers (1.5 cm diameter) that are followed by dry, flattened, oval, light brown fruit (1 cm long).
Why is it weedy?
One plant produces up to 50,000 viable seeds that spread rapidly along water courses. Forms dense colonies suppressing the growth of native plants and grasses, dies down in winter, leaving infested banks bare of vegetation and liable to erosion or to reinvasion by weed species.
How does it spread?
Seeds scatter around the parent or are spread by water.
What damage does it do?
Poisonous to humans - touching it, or exposure to dust from weed-eating, can irritate skin and cause blisters and swelling. Sap from leaves and stems is highly toxic and can cause 'photodermatitis' or 'photosensitivity' (the skin becomes very sensitive to sunlight and may suffer blistering, pigmentation and long-lasting scars). Contact with the eyes can lead to temporary or permanent blindness. Areas which come into contact with this plant should be washed immediately and protected from direct sunlight, seek medical advice.
Which habitats is it likely to invade?
Wasteland, road ditches, tree land areas and river or stream banks, it prefers rich, moist soils.
What can I do to get rid of it?
Always wear gloves and eye protection, and cover arms and legs when working near this plant. Contaminated clothing and tools are potentially hazardous also. Wash any skin that comes in contact with the plant immediately.
1. Hand pull whole plants (spring-summer) before they set seed.
2. Cut down (summer): cut the stem below ground level during flowering but before seed sets. Spray regrowth in February or March if necessary with glyphosate (150ml/15L).
3. Overall spray (spring): glyphosate (150ml/15L). Spray again in February or March if necessary.
CAUTION: When using any herbicide or pesticide, PLEASE READ THE LABEL THOROUGHLY to ensure that all instructions and directions for the purchase, use and storage of the product, are followed and adhered to.
What can I do to stop it coming back?
Seeds may remain dormant in the soil for at least 5 years, so prevent germination by oversowing with other species.
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