Scientific name: Heracleum mantegazzianum Also known as: Cartwheel Flower, Giant Cow Parsnip, Efwr Enfawr Key Facts • Giant hogweed is a highly invasive plant that can grow up to 5m tall with 1.5m wide leaves and 80cm flowering umbels. Do not touch – sap causes blistering of the skin. • Giant hogweed is listed under schedule 9 of the Wildlife and Countryside Act 1981. It is an offence to plant or cause this species to grow in the wild. • The plant material is also classified as ‘controlled waste’ under the Environmental Protection Act 1990. • Giant hogweed was introduced as an ornamental plant to the British Isles in the 19th century from South West Asia. • It is found occasionally throughout Wales but mainly in the east and south west by streams and rivers and along roadsides. • The plant is spread by seed transported by both wind and water. Description Giant hogweed is an impressive plant, related to cow parsley, which can grow up to 5m tall. It produces large umbrella-shaped clusters of white flowers in June and July up to 80cm across. Public information on invasive species in Wales Giant hogweed Lifecycle The plant is a biannual or short-lived perennial, forming a rosette of leaves in the first year and flowering in the second year onwards. Small plants may stay as rosettes of leaves for up to 4 years. The plant dies back in the autumn and survives over winter as a large fleshy tap root. The plant produces around 50,000 seeds each year which can remain viable for up to 15 years. 1st year Seedlings emerge Grows as a rosette of leaves 2nd year onwards Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Stem starts to elongate Flowering Seed produced All years Plant dies back and becomes dormant
Transcript
Scientific name: Heracleum mantegazzianum
Also known as: Cartwheel Flower, Giant Cow Parsnip, Efwr Enfawr
Key Facts • Giant hogweed is a highly invasive plant that can grow up to
5m tall with 1.5m wide leaves and 80cm flowering umbels. Do not touch – sap causes blistering of the skin.
• Giant hogweed is listed under schedule 9 of the Wildlife and Countryside Act 1981. It is an offence to plant or cause this species to grow in the wild.
• The plant material is also classified as ‘controlled waste’ under the Environmental Protection Act 1990.
• Giant hogweed was introduced as an ornamental plant to the British Isles in the 19th century from South West Asia.
• It is found occasionally throughout Wales but mainly in the east and south west by streams and rivers and along roadsides.
• The plant is spread by seed transported by both wind and water.
Description Giant hogweed is an impressive plant, related to cow parsley, which can grow up to 5m tall. It produces large umbrella-shaped clusters of white flowers in June and July up to 80cm across.
Public information on invasive species in Wales
Giant hogweed
Lifecycle The plant is a biannual or short-lived perennial, forming a rosette of leaves in the first year and flowering in the second year onwards. Small plants may stay as rosettes of leaves for up to 4 years. The plant dies back in the autumn and survives over winter as a large fleshy tap root. The plant produces around 50,000 seeds each year which can remain viable for up to 15 years.
1st yearSeedlings emerge
Grows as a rosette of leaves2nd year onwards
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Stem starts to elongate Flowering Seed producedAll yearsPlant dies back and becomes dormant
Lookalikes There are many other white flowered umbellifers similar in looks to Giant hogweed; such as Common hogweed (Heracleum sphondylium) Cow parsley (Anthriscus sylvestris), Wild angelica (Angelica sylvestris) and Hemlock (Conium maculatum). But it is difficult to confuse giant hogweed with any other plant because of its size, even early in the season, as its leaves will be considerably larger than any other leaves. Giant hogweed is quite distinctive even from its nearest relative Common hogweed, due to its deeply lobed, spikey leaves.
Leaves – Dark green deeply divided leaves, spiked at the ends, up to 1.5m wide and 1.3m long with reddish purple spotted leaf stalks. Bristles occur on the underside of the leaves.
Stem – Reddish purple blotchy and ribbed with sharp bristles usually unbranched. The stem is up to 5 to 10cm in diameter and hollow.
Flowers – White flowers with petals up to 12mm long and arranged in flat topped umbrella shaped clusters (umbels). These umbels can be up to 80cm across.
Seeds – These are flattened and oval with dark stripes, two on one side and four on the reverse, approximately 10mm long and 7mm wide.
Why is it a concern?Giant hogweed is very competitive because of its large size and its rapid growth rate. It outcompetes native vegetation for space and resources. When the plant dies back in the winter it leaves bare areas which are more susceptible to erosion, this can lead to large sections of river bank being eroded. It can be invasive, producing large numbers of seed every year which can survive in the soil for up to 15 years. The sap of Giant hogweed contains a toxic chemical which sensitises the skin and leads to severe blistering, when exposed to sunlight. This reaction can reoccur for many years.
Management Control Options
There are several options for control both chemical and non-chemical. The aim is to control existing plants, prevent seed return and prevent movement of any material off site. The site will need to be revisited annually in the spring as new plants could regenerate from seed which survives in the soil for about 15 years. Contractors may be of value in controlling large infestations given sap hazard.
Root removal or root cuttingIn the early spring (April/May) before the leaves are too large, the whole plant can be completely removed by digging the tap root or by cutting the tap root approximately 15cm below ground using a sharp object such as a spade to separate the root from the stem. As long as the upper 15cm of root is removed the plant will not regrow. The site should be checked again in the mid-summer for regrowth and the process repeated. The root sections should be left to dry out in a secure location exposed to direct sunlight for two weeks to ensure the root sections are dead. Once the root sections are dead they can be burnt or left to rot. Avoid taking the roots off site for disposal and do not put in the recycling bin. There are no specific laws preventing a householder from having a bonfire but there are laws for the nuisance they cause. For further information see https://www.gov.uk/garden-bonfires-rules
Mowing and cutting The plant can be mowed when it is small and continue to mow throughout the growing season. Do not mow the plant if it is larger than your mower and never mow if there is a flower or seed head. Plants must be cut at least three times during the growing season for several years. Mowing will eventually kill the plants by exhausting the energy in the tap root. If there is a flower head remove this first (see below).
Legislation and responsibilitiesGiant hogweed is listed under schedule 9 of the Wildlife and Countryside Act 1981. It is an offence to plant this species or to cause it to grow in the wild. There is no obligation to eradicate this species from your land or to report its presence to anyone. However, if this species spreads to the wild or to a neighbour’s property then you could be liable.The plant material is also classified as ‘controlled waste’ under the Environmental Protection Act 1990. Plant material can only be transported and disposed of by someone licenced. Natural Resources Wales holds a register of licence holders see https://www.wastecarriersregistration.naturalresourceswales.gov.uk/cy/registrations/search
WARNING – Giant hogweed contains sap that is released when the plant is touched or cut. Contact with the sap causes the skin to become sensitive to sunlight leading to painful blisters, this reaction may occur for several years. Before working with giant hogweed full protective clothing (overalls, gloves, goggles and hat) must be worn to stop any sap from getting on to skin.
Where it is found in WalesIt is found occasionally throughout Wales but mainly in the east and south west by streams and rivers and along roadsides. Each plant produces up to 50,000 seeds and these can be spread by water especially when in flood and can rapidly colonise bare areas of bank. Seeds can also be spread by humans through them sticking to car tyres or attaching to clothing and through picking of umbels (seed heads) for decoration purposes. Seeds can also attach to animal fur. Seeds can be dispersed further if blown across frozen or snowy surfaces.
Caution – do not cut with a strimmer as it can flick toxic sap onto skin and clean mowers after use to remove the toxic sap.
References and further sources of information Find the Wildlife and Countryside Act 1981 on the Legislation.gov.uk website.
Find the Environmental Protection Act 1990 on the Legislation.gov.uk website.
Nielsen, C., Ravn, H. P., Nentwig, W. and Wade, M. (eds.) 2005. The Giant Hogweed Best Practice Manual. Guidelines for the management and control of an invasive weed in Europe. Forest & Landscape Denmark, Hoersholm, 44 pp.
Booy, O., Wade, M. (2007). Giant Hogweed Management in the United Kingdom, published by RPS Group plc ISBN 978-0-906269-04-6
Booy, O., Wade, H. and White, V. (2010) Giant Hogweed Identification Sheet [Online]. Available at https://secure.fera.defra.gov.uk/nonnativespecies/downloadDocument.cfm?id=30.
Centre for Aquatic Plant Management (CAPM) (2004) Information sheet 4, Heracleum mantegazzianum Giant Hogweed. Centre for Ecology and Hydrology
Giant Hogweed - GB Non-native Species Secretariat website. https://secure.fera.defra.gov.uk/nonnativespecies/factsheet/factsheet.cfm?speciesId=1705
If the Giant hogweed is near a water course, permission for treatment with herbicides must be given by Natural Resources Wales prior to application.
If the Giant hogweed is on a designated site such as a Site of Special Scientific Interest (SSSI), Special Protection Area (SPA) or Special Area of Conservation (SAC) then written permission will be required before treatment from Natural Resources Wales.
Flower seed head removal The flower heads can be cut off after the seeds have formed but before they start falling off the head (late August/September). If the plant is small the best method is to bag the head first and cut the stem below. This can be done with a bin liner and aims to stop any seeds from falling. Seed heads should be allowed to dry out as above and burnt or left to rot. This method will not kill the plant but prevent it from seeding.
Herbicide control Herbicides can be applied to the plant foliage between late April and early June and again in July or August. Spray is usually directed on to the leaves of the plant and the sites are revisited annually to check for regrowth of old plants or new plants from seed.
Triclopyr is the preferred product early in the season as it is selective (does not kill grasses) and has an effect for 6 weeks after application. Glyphosate is also used at a similar timing but it is non-selective so will kill all other vegetation. Both herbicides are taken into the plant via the leaves and stems and moved to the roots (translocated).
After treatment
After removing invasive non-native species, it is important to re-establish native species of plants. This will help to achieve control, reduce soil erosion and provide competition to prevent further infestation.
This information leaflet has been produced for the Welsh Government
by ADAS UK Ltd. www.adas.uk
Amenity Assured Compliant Contractors More information from BASIS: www.basis-reg.co.uk 01335 343945
National Association of Agricultural and Amenity Contractors have a list of contractors in the Amenity sector
It may be appropriate to employ a specialist contractor for assessing the best method of control and to apply any pesticides. Good contractors will have the following:
• A BASIS certified practitioner with knowledge of control of invasive weed control to recommend appropriate chemical control options.
• A spray operator who holds the appropriate National Proficiency Tests Council (NPTC) certification for herbicide use or works under the direct supervision of a certificate holder.
• If sprays are to be applied in or near water, the person carrying out or supervising the spraying must have the appropriate aquatic part of the qualification.
Lists and details of contractors can be found through the sites below.
Management Control Options - Continued
Selecting a contractor
Welsh GovernmentNatural Environment and Agriculture
