This section gives information about plants, insects and other non-natives that are harmful to our environment. For some a specific place to report sightings is given, otherwise contact parks@barnet.gov.uk to report.
For more information on what’s listed here and other invasive plants, animals and insects, see the Department of Food and Rural Affairs (Defra), Non-Native Species Secretariat.: https://www.nonnativespecies.org/non-native-species/species-alerts/#Species_53
Giant hogweed Heracleum mantegazzianum
DO NOT TOUCH!
Legislation
Giant hogweed is an invasive species, originally native to Asia, that is now widespread across the UK. It is listed on Schedule 9 & 14 of the Wildlife and Countryside Act 1981 (as amended), making it an offence to allow to spread (either intentionally or recklessly). It is also legislated under the Environment Protection Act 1990, where it is classed as “controlled waste” and must be disposed of safely at a licensed landfill site.
Identification
Giant hogweed is in the plant family Umbelliferae, and looks similar to cow parsley, angelica and hogweed. Giant hogweed is HUGE, it can grow up to 5 m tall and has very thick stems, almost like a small tree, with large pointy leaves and huge flower heads.
Leaves
Giant hogweed has large leaves, up to 1.5m wide and 3m long, that are deeply divided into smaller leaflets. The underside of the leaf is hairy. It looks a bit like a rhubarb leaf, with irregular and very sharp or jagged edges.
Stems
The stems are hollow with ridges and have a thick circle of hairs at base of each leaf stalk. They are green with purple blotches, and have stiff, white, bristly hairs.
Flowers
Giant hogweed flowers appear in June and July. They are small and white (they can also be slightly pink) and are clustered on umbrella-like heads (umbels), which can reach a diameter of 60cm. All the flowers on the umbel face upwards.
Risks
Health
Chemicals in the sap cause photodermatitis or photosensitivity, and react to sunlight. If the sap comes into contact with skin, can cause effects ranging from a mild rash, blistering and scarring which may require hospital treatment. Do not touch giant hogweed, even if it has been treated with herbicide.
Japanese Knotweed Reynoutria japonica
Legislation
Japanese knotweed is an invasive species, originally native to Japan, that is now widespread across the UK. It is listed on Schedule 9 & 14 of the Wildlife and Countryside Act 1981 (as amended), making it an offence to allow to spread (either intentionally or recklessly). It is also legislated under the Environment Protection Act 1990, where it is classed as “controlled waste” and as such must be disposed of safely at a licensed landfill site.
Identification
Japanese knotweed is a tall plant with large triangular leaves, hollow, red stems that look a bit like bamboo, and small, white, tufty flowers that appear in late summer and autumn.
Leaves
The leaves are a light green colour, with red or purple flecks. They are heart or shovel-shaped and have a pointed tip. They shoot out from nodes in a zig-zag pattern. New leaves are rolled up with dark red veins while mature leaves can grow up to 20cm. Stems and Rhizomes.
Stems and Rhizomes
The main stems look similar to bamboo, and are green with purple and red speckles, hollow and grow to 2-3 metres in height. The leaves grow in a zig-zag pattern. The rhizome (roots) are black with an orange centre and can grow up to 2cm a day.
Flowers
Japanese knotweed flowers are cream/white in colour, approximately 0.5cm wide, and form clustered panicles that can grow to 10cm. They bloom in very late summer (August/September).
Risks
Damage to Infrastructure
Japanese knotweed rhizomes grow fast and can cause damage to structures. The rhizomes can grow through tarmac and concrete, breaking the surface open, and often cause damage to the foundations of buildings, pavements, and other infrastructure. The rhizomes can spread up to 7m underground and the removal must be done by a specialist contractor to ensure eradication is successful. If even 1cm of rhizome is left in the soil, the plant will re-establish.