Himalayan or Indian balsam (Impatiens glandulifera) was introduced to Britain in 1839, but escaped from gardens and rapidly colonised riverbanks and areas of damp ground. Himalayan balsam grows in dense stands that suppress the growth of native grasses and other flora. In the autumn, the plants die back, leaving the banks bare of vegetation and vulnerable to erosion.

Native range

Western Himalayas

Stem

Pinky-red colour
Up to 3m tall - tallest annual plant in Britain
Hollow and jointed
Sappy and brittle

Leaves

Spear-shaped, with serrated edges
Shiny and dark green with a dark red midrib
Up to 150mm long
Opposite or in whorls of three

Flowers

Purplish-pink to pale pink
Slipper-shaped, on long stalks
June – October

Seeds

White, brown or black
Produced from July – October
4-7mm diameter
4 – 16 seeds per pod

Control

Control measures should aim to prevent flowering and if this is achieved before seeds are set, eradication is possible in two to three years.

Chemical control

Can use glyphosate or 2,4-D amine. Need to be used whilst plant is actively growing in early spring for best effect.

Cutting/mowing/strimming

Cut at ground level using a scythe, before the flowering stage in June. Do not cut earlier as this promotes greater seed production in any plants that regrow. Cutting should be repeated annually until no more growth occurs.

Pulling

Shallow-rooted plants can be pulled up very easily and disposed of by burning or composting, unless seeds are present.

Grazing

Grazing by cattle and sheep is effective from April throughout the growing season. It should be continued until no new growth occurs.

Giant hogweed (Heracleum mantegazzianum) was introduced to Britain in 1893 as an ornamental plant. It escaped from gardens and now colonises many areas of wasteland and riverbanks. It forms dense colonies that suppress the growth of native plants and grasses, leaving the banks bare of vegetation in winter and increasing the risk of erosion and recolonisation from seeds washed downstream.

Legislation: The Wildlife and Countryside Act 1981 provides the primary controls on the release of non-native species into the wild in Great Britain. It is an offence under section 14(2) of the Act to ‘plant or otherwise cause to grow in the wild’ any plant listed in Schedule 9, Part II. This includes Giant hogweed.

Health Hazard

The stems, edges and undersides of the leaves bear small hairs containing poisonous sap, and the slightest touch causes painful blistering and severe skin irritation. Unshaded habitats with high soil nitrate levels tend to produce greater quantities of toxins in the plant. Contact with cut material in sunlight produces a skin reaction in almost all cases. Blistering symptoms occur 24- 48 hours after exposure, and dense pigmentation is visible after 3 – 5 days. This may persist for 6 years or more. Protective clothing must be worn.

Native range

Caucasus mountains.

Lifecycle

Perennial plant that takes up to 4 years to mature and flower, after which it dies.

Stem

Green with dark-red or purple blotches. Hollow Up to 100mm across Up to 5m tall.

Leaves

Dark green, in a rosette Jagged appearance and spiky at the ends Lower leaves up to 1.5m long.

Flowers

White Several hundred in large umbrella-like flower heads up to 500mm Across. June – July.

New plants

Each flowerhead produces up to 50,000 seeds (approx. 10mm x 7mm) that are easily dispersed by water, so the plant disperses rapidly along watercourses. Seeds may remain viable for up to 15 years.

Control

Aim – to kill the plant or prevent flowering.

Chemical control is most effective. 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.

Non-chemical control Cutting down stems with a sharp scythe before flowering will help control this plant. Flail mowing is possible but with extreme caution due to the risk of being sprayed with sap. Protective clothing should be worn.

The crown may be dug out just below ground to prevent regrowth this provides good control.

Grazing by cows and sheep will suppress growth but will not eradicate it. It is essential to establish vegetation quickly after control measures have been applied, as dense grass sward tends to discourage seed germination.

Disposal

Should be taken to a landfill site or by piling on site and composting.

Japanese knotweed was brought to Britain as an ornamental garden plant in the mid-nineteenth century. However since then it has become widespread in the wild and causes serious problems by displacing native flora and causing structural damage.

Legislation: The Wildlife and Countryside Act 1981 provides the primary controls on the release of non-native species into the wild in Great Britain. It is an offence under section 14(2) of the Act to ‘plant or otherwise cause to grow in the wild’ any plant listed in Schedule 9, Part II. This includes Japanese Knotweed.

There are 3 species of invasive knotweed in the UK. Japanese knotweed (Fallopia japonica) – the most widespread and troublesome bankside species. Giant knotweed (Fallopia sachalinensis) Hybrid knotweed (Fallopia x bohemica) – a cross between Japanese and giant knotweed.

Native range

Eastern Asia

Stem

Up to 2-3m tall.
Green, with red or purple specks.
Forms dense cane-like clumps.

Leaves

Green, shield or heart-shaped, with a flat base.
Up to 120mm long.

Flowers

Creamy clusters borne on the tips of most stems.
August – October

Roots

Consist of rhizomes, which are yellow, when cut.
The rhizome system can reach 7m from the parent plant and can be up to 3m deep.

New plants

New plants can grow from a piece of rhizome the size of a little finger nail and the crown, located at the base of the stem will also produce new plants.

Control

Near water chemical control can be achieved with herbicides containing glyphosate. Spraying both the top and underside of leaves improves control.

Cutting

Should be done extremely carefully using a hand sythe to avoid spreading stem fragments. Flail mowing must not be carried out. Continue cutting every 2-4 weeks to reduce both above and below ground biomass.

Pulling

Uproot stems by pulling from the base – best done from June onwards.

Grazing

Grazing of shoots by horses, sheep and goats keeps the plants in check, provided previous dead growth is removed.

Digging

Digging out rhizomes and disposing of the spoil is an expensive option and often impracticable. The spoil can be removed from a site as special waste, disposed on-site at least 10m deep, or the material can be sieved through a 20mm mesh and the spoil reused on site.

Spring Cut new growth. Dig out rhizomes or spray new growth with Glyphosate. Excavate soil and dispose of on site or take to landfill as special waste, under license. Summer Cut new growth. Dig out rhizomes or spray with glyphosate. Autumn Cut new growth. Dig out rhizomes and spray with glyphosate. This is the most effective time for glyphosate application.

Disposal

The stems die back in winter but take up to 3 years to decompose. Japanese knotwood crowns should neither be composted nor removed from a site without a waste license. Burn cut stems on site or bury 10m deep.