Himalyan Balsam

Species Description


Scientific name: Impatiens glandulifera

 Identification sheet


Native to: West and central Himalayas


Habitat: In Britain, Himalayan balsam prefers moist and semi-shaded places, waste ground and thin woodland. It is particularly prevalent along streams and riverbanks, using water to disperse its seeds. 


Introduced to the UK in the mid 19th century as an ornamental, this annual plant has spread rapidly.  Its success is due to vigorous growth, shade tolerance, effective seed dispersal and high germination rate.  The plant can grow to 2 metres in height and forms dense monoculture stands. It out competes other bank-side vegetation, decreasing biodiversity.  When the plant dies in the autumn it leaves the bank bare and vulnerable to erosion. In the Ribble catchment, Himalayan balsam is widespread and extensive, particularly along the mid and lower sections of the river. 


Distribution in Lancashire

Himalayan balsam is widespread in Lancashire but tends to be more prevalent in areas of higher population density and in the lower reaches of river systems. All the main rivers in Lancashire have been colonised by Himalayan balsam. This map shows the 1km squared distribution within the county.



In the Ribble catchment, Himalayan balsam has been surveyed in detail along most watercourses. The map below shows the watercourses of the catchment which have been colonised by balsam (in red). This map demonstrates how Himalayan balsam spreads downstream along watercourses, using the flow of water to disperse its seeds.



Further Information

Dispersal and Reproduction

Each plant may produce up to 800 seeds which can be ejected up to 7 metres from the parent. The seeds float in water and are dispersed over large distances by streams and rivers. Seeds germinate from February onward and grow rapidly. Flowering occurs from July to October, with seeds produced from mid-July onward.

Known Predators

In Britain, sheep and cattle graze balsam indiscriminately, eating leaves, stems and flowers. The elephant hawk-moth and two species of aphid also feed on the plant. Trials of a rust (Puccinia sp.) as a potential new biological control agent are currently underway.

Impacts


Environmental

Balsam shades out and crowds out many native plant species. It also competes with native flowers by exploitation as it produces more nectar, attracting more pollinating insects.  


Economic

Having become dominant in its invaded habitat, the shallow root system can promote erosion during autumn and winter, with the subsequent destruction of bankside structure. Dense stands can impede water flow at times of high rainfall, thereby increasing the likelihood of flooding.

Management

Control measures should aim to prevent flowering, and are best carried out before June for maximum effectiveness. All Himalayan balsam in an area should be controlled as any plants setting seed will result in many more plants next year. The most effective strategy for control is to start at the outer edge of the patch and work towards the centre, or on watercourses to start at the upstream extent and work down.

Mechanical

  • Cutting - cut at ground level using a scythe, machete, flail or strimmer before the flowering stage in June. Cutting earlier than this may promote greater seed production from 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.

Chemical

  • Glyphosate - treat with a weed wipe in mixed stands, or by foliar spray in dense stands, before flowering. If all plants are controlled, then spraying should only be required for two to three years.
  • 2,4-D amine - treat during early spring at the rosette stage for effective control.

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