Bracken fern

Download PDF version 318kb

Bracken fern (Pteridium esculentum)

Distribution | Description | Lifecycle | Spread |Impact | Control & Management | Legislation

Bracken fern, or bracken, is a native perennial fern found in open forest, or on cleared land where it can form extensive colonies and be a troublesome weed that is difficult to eradicate.

Distribution

Bracken is found in most temperate areas in Australia as well as some overseas countries such as New Zealand. In New South Wales it is found on the north, central and southern coastal areas, the tablelands and, to a lesser extent, the slopes.

Description

Bracken has erect, stiff fronds up to 1.5 m high, but usually around 0.6–1 m. The fronds are bright green and coiled when they emerge. As they unfurl and expand they become harder and darker. Fully mature fronds are a dark emerald green. The older fronds are smooth on top with fine hairs underneath.

Bracken has an extensive, spreading root system, with rhizomes or underground stems that form a vast network in the soil and give rise to new shoots. The rhizome is 2–10 mm in diameter and can be several metres long; it is densely covered with dark, red-brown hairs. The root system can amount to a biomass of 30–100 tonnes per hectare.

Dead fronds may remain standing for several years and established stands of bracken usually contain a mixture of green and dead fronds.

As bracken is a true fern it does not produce flowers or seeds, but instead produces spores in bodies called ‘sori’, which occur in a continuous line on the undersides of the fronds. The spores are minute.

Lifecycle

Bracken is a perennial fern, but the fronds emerge in the spring and die off in autumn. In colder areas fronds will live for only one year, but they can live for two years where conditions are milder.

Bracken spores are produced and usually dispersed in late summer to autumn. This can vary in different years and across different locations. Spores germinate in moist, sheltered situations.

Spread

Infestations of bracken spread locally through the hardy, persistent root system. This causes infestations to thicken and grow larger over time.

Bracken spores can be carried long distances by wind. Spread can also occur by the movement of fragments of rhizome carried to uninfested areas by machinery.

Impact

Bracken’s extensive root system has many fine roots in the soil surface which enables the fern to compete effectively with pasture species for moisture and nutrients.

Old, dead fronds often remain in the stand and form dense mulch on the ground, inhibiting the germination and growth of other plants, including pasture species. In dense undisturbed bracken stands, the canopy can crowd out and shade other species and dominate an area.

Bracken regenerates rapidly after fire and may dominate recently burned areas.

Bracken causes serious problems during the establishment of pine forests, and it is causing concern in some national parks where bushfires have thinned the over-storey and encouraged the development of a thick bracken understorey, reducing the diversity of the native plant community.

It can also be a problem along roadsides, fence lines and railway lines, and on industrial sites. It provides a harbour for noxious animals such as pigs, foxes and rabbits and it has few natural enemies.

Stages of development of bracken fern

Control and management

A combination of measures over the long term is required for the control of bracken.

Control strategies must be aimed at weakening and killing the plant root system and rhizomes. A large amount of the plant’s energy is stored in the root system, which allows the plant to regenerate after damage. Repeated control techniques will reduce and eventually kill the root system and prevent further regeneration.

Hygiene

Ensure that equipment used for cultivation is cleaned before it is moved from bracken-infested areas to ‘clean’ areas. Sections of rhizome broken off and carried to un-infested areas by machinery may establish and create new infestations.

Cultivation

Combining cultivation over two or three consecutive years with cropping before the establishment of a competitive pasture is effective for the control of bracken.

Cultivate in summer to break up the rhizomes and bring them to the surface, where they dry out and die. Cultivation to 15–20 cm is deep enough for good control. Disc ploughs and rotary hoes are suitable but tined implements are best as they drag the rhizomes to the surface. If infestations are thick and well established they may have to be slashed or burned before cultivation to avoid blocking up machinery.

Unfortunately, cultivation is not suitable on steep country where soils are shallow, infertile and easily eroded.

Slashing

Repeated slashing can eventually control bracken, but it needs to be done for a minimum of three consecutive years to deplete the plant energy reserves stored in the rhizome.

For greatest effect, destroy the new fronds as they reach the unfurled stage. At this point the fronds have used up the maximum amount of energy from the rhizome for growth.

Slashing needs to be repeated regularly: about once every four weeks during the peak growth season from late spring to late summer. Work conducted in Victoria indicates that three cuts a year (December, January and March) appear to be more effective than two.

It is more effective to concentrate on small areas by slashing frequently rather than try to control larger areas but slash less frequently.

Unfortunately, steep topography can also make slashing impossible in some areas.

Rolling/crushing

Rollers crush and bruise the fronds but are less effective than cutting. As with slashing, repeated crushing of the fronds may eventually wear down the energy reserves in the rhizome.

Using a roller is a quicker, more versatile and less expensive method than either slashing or cultivation. Rollers with a ribbed or irregular surface are best.

Burning

Burning alone is not an effective control technique.

Bracken regenerates rapidly after burning because the underground rhizome is unharmed. However, burning can be used to reduce the amount of dead fronds in the winter before a planned herbicide application or cultivation.

Herbicides

Herbicides are available for use on bracken in pastures and in environmental situations. There is no herbicide that will provide complete control of bracken with a single application. However, there are several herbicides that, when used as part of a program, can provide effective control.

A list of recommended chemicals and application techniques can be found in the NSW DPI publication Noxious and Environmental Weed Control Handbook. For full details on the use pattern of these herbicides, consult the product labels.

Herbicides can be applied with a boom spray, by motorised mister, wipers or knapsack.

To ensure effective translocation to the root system, herbicides must be applied when the majority of fronds are fully unfurled from November/December to April/May. The fronds transfer their food reserves into the rhizome in late autumn, and herbicide application is most effective at this time.

Do not cut or otherwise damage bracken for at least 8–12 months before spraying. Do not slash, burn, cultivate or graze for at least 6 months after treatment as sprayed plants may take a number of months to die off.

There are a number of things to remember when applying chemicals to ensure the best results.

Where adjuvants are recommended to be added to the herbicide mix, it is particularly important to follow the recommendation as penetration of chemical into the cuticle (surface) of the frond is necessary to increase the chance of success. This is especially important when using herbicides on older fronds as the cuticle of the leaf is thicker, inhibiting the entry of herbicide into the plant.

Herbicides can also be used effectively as part of a pasture re-sowing strategy. The bracken could be slashed in the winter/spring and then herbicide applied in the following autumn to fully expanded fronds, before any frost. Remember to leave at least 8 months from slashing to herbicide application to allow time for regrowth. Results may not be visible until the next season and then a follow-up application is recommended on any new fronds that have emerged.

Pasture establishment and management

Pasture improvement is an essential part of any plan to control bracken. Most control options will eventually fail if they are not followed up by strategies that encourage a competitive pasture.

If sowing a pasture, choose species or varieties of grasses and legumes that will be suited to the soil type and climate of the area. Consult your local agronomist for recommendations.

Legislation

Bracken fern is a native plant. As such, management of this species is subject to native vegetation legislation. Land managers should contact their local Catchment Management Authority (CMA) for information on managing this species. In cases where bracken fern has regrown since 1 January 1990, consent will not be required before treatment. It is suggested that the CMA be contacted in all other cases to seek approval.

Acknowledgments

Authors:
Lori McWhirter District Agronomist, Goulburn
Harry Kemp Former District Agronomist

This Primefact is based on Agnote DPI-506, Bracken fern. NSW Department of Primary Industries.

The authors would like to acknowledge the technical input of Dr Chris Bourke, Bob Trounce and Birgitte Verbeek.

References

• Agnote DPI-506, first edition 2004. Bracken fern. NSW Agriculture.
• Agfact P7.6.3 1981. Bracken fern. NSW Agriculture.
• Agriculture WA 1999. Control of bracken fern using the wick wiper. Department of Agriculture (Moore J), Western Australia.
• DNRE 1998. Bracken fern poisoning of cattle. Department of Natural Resources and Environment (Jeffers M), Victoria.
• DPIWE 1999. SS 125 – Bracken (Pteridium esculentum). Tasmanian Department of Primary Industries, Water and Environment, Hobart.
• Everist SL 1974. Poisonous plants of Australia. Angus and Robertson, Sydney.
• Robinson L 1991. Field guide to the native plants of Sydney. Kangaroo Press, Kenthurst NSW.