• Key characteristics
  • Biology
  • Impacts
  • Control
  • Further information

  • Bracken is a fern, producing spores not seeds, which is native to New Zealand
  • It spreads by means of underground stems (rhizomes) that send up leaves at intervals
  • It is taller-growing than ring fern, usually up to 1.5 m tall
  • Rhizomes are stiff, 5-15 mm thick, and branch frequently
  • Stipes (leaf stalks) are erect, rigid, dark brown, glossy but hairy when young
  • The main axis of the leaf is stout, brown and hairy when young
  • Fronds (leaves) are dark green, up to 1 m long, unrolling as they grow
  • Spore-bearing organs (sporangia) are borne along the underside margins of the smallest leaf segments
  • Although bracken has been used as human food in New Zealand, parts of the plant are toxic and carcinogenic to humans and livestock
  • Plants are very ‘plastic’ in behaviour, being small and stunted in dry rocky places and sometimes reaching 4 m high on forest margins
  • Dry, dead fronds burn very readily.

Origin

  • Bracken, like ring fern, is a native to New Zealand. Pteridium esculentum is also found in Australia and the Society Islands but Pteridium aquilinum, a very close relative, is widespread throughout the world
  • Pteridium esculentum rapidly increased in area in New Zealand as early humans cleared and burned forests and it is now common throughout the country in open habitats.

Life cycle

  • Bracken is a fern, reproducing by spores that germinate to produce a small prothallus This develops male and female sexual organs that in turn produce male and female gametes, resulting in the formation of a new fern plant
  • Bracken spores are very small and are released between late summer and autumn They can be carried for considerable distances on air currents.

Benefits

  • Bracken rhizomes were used by Maori as a starchy food
  • Dry bracken stalks have multiple uses as play things, from arrows to kite structures.

Impact on farming

  • Tall-growing bracken can make stock access and mustering very difficult

Impact on pasture

  • Bracken, like ring fern, can form very dense cover, smothering useful pasture species
  • Bracken uses valuable soil nutrients for growth and these nutrients are locked up in the fronds until they eventually break down.

Impact on stock

  • Some strains of bracken appear to be more toxic than others, but all can be poisonous to livestock if large quantities are eaten
  • Bracken contains carcinogens that can cause cancerous lesions in livestock.

Impact on forestry

  • Bracken competes strongly with young trees and is also a fire risk.

  • Bracken is rhizomatous and difficult to kill
  • Bracken commonly grows in poorer grazing land, therefore, its control may not be economically feasible.

Grazing

  • Grazing is not an effective method of control, but heavy treading by cattle can be used to crush the new fern shoots as they are emerging.

Mowing

  • Repeated mowing or crushing can be used as control measures. However, where bracken grows on steep hillsides this may not be practical.

Pasture species/cultivars

  • Establishment of new competitive pasture species, suited to local conditions, can be used after initial clearance of fern, and may, if adequately limed and fertilised, help to prevent reestablishment.

Forestry

  • Trees can form a dense canopy and shade out bracken but the trees must be protected from bracken when young.

Chemical control

  • Bracken is generally very difficult to kill with herbicides, though it is susceptible to glyphosate and high rates of metsulfuron, both of which are damaging to grasses
  • Two selective herbicides – asulam and primisulfuron will control bracken within pine forests. Asulam should be applied without surfactant when releasing young trees
  • Asulam (Asulox) is selective in pastures and should be applied when bracken fronds are fully expanded but before they are affected by frost (late summer to early autumn). Its effect on the bracken will not be obvious until the following spring

Biocontrol

  • No biological control agents are available for either species.

  • Massey University Weeds Database 2014. Bracken: Pteridium esculentum (accessed 19 May 2015).
  • McGlone MS, Wilmshurst JM, Leach HM 2005. An ecological and historical review of bracken (Pteridium esculentum) in New Zealand, and its cultural significance. New Zealand Journal of Ecology 29: 165-184.
  • Popay I, Champion P, James T 2010. An illustrated guide to common weeds of New Zealand. New Zealand Plant Protection Society, Christchurch, New Zealand. 416 p.
  • Young S 2013. New Zealand Novachem Agrichemical Manual. Agrimedia Ltd, Christchurch, New Zealand. 767 p.