Information and Advisory Note Number 24                                               Back to menu

Bracken control

1. Introduction

1.1 Bracken (Pteridium aquilinum) is a vigorous and aggressive fern, spreading rapidly by means of strong underground stems or "rhizomes". It has a wide soil tolerance, doing particularly well on deep acidic soils, but it is intolerant of waterlogged soils. Bracken is a major weed in many upland and upland margin areas, causing management problems in agriculture, forestry, conservation, game management and recreation.

1.2 Concern about the spread of bracken has led to the development of a number of techniques for its control. This information and advice note puts the problem into perspective and aims to provide farmers with guidance on where, when, how and if bracken should be controlled. Complete eradication of bracken is nearly impossible, and is not necessarily desirable

2. Values of bracken

2.1 Despite its effects on other habitats, bracken can be an important habitat in its own right.

2.2 Bracken is an important characteristic of the upland landscape, particularly in the autumn and winter.

3. Why control bracken

3.1 Key reasons for managing bracken are to:

3.2 In ESAs bracken control may be a requirement of Tier 2 management, necessary to safeguard areas of herb-rich grassland, heather moorland or archaeological features

4. Where to control bracken

4.1 Bracken control is appropriate in the following circumstances.

5. Where not to control bracken

It is not always appropriate to undertake control of bracken as environmental damage may result at some sites. The following areas should be avoided.

5.1 Treatment with the herbicide asulam should be avoided in steep valleys with high humidity and rocky areas where other ferns (such as royal fern and lemon-scented fern) may flourish, as well as sites where other susceptible species occur (see below).

5.2 Where spray damage may occur on nearby forestry plantations. Most species are tolerant of asulam at the normal application rate, however young trees may be scorched if they receive direct spray. Willow and western hemlock are particularly sensitive.

5.3 Sites where there is little benefit from control and where bracken forms a substitute woodland community, supporting interesting plants and insects.

5.4 Steep sites with deep bracken litter and little opportunity for the recovery of vegetation following treatment - bracken control on these sites can lead to severe erosion.

6. Factors affecting control methods

6.1 Factors to consider when assessing the suitability of various bracken control methods include slope, cover, underlying vegetation, litter and the nature of the rhizome system.

6.2 Control of bracken is not achieved instantly. It is a long-term management process, requiring monitoring followed by repeated follow-up control.

6.3 Research suggests that there are two basic types of bracken rhizome - superficial surface rhizomes and deeper, storage rhizomes. While spraying is effective on the bud-bearing surface rhizomes, it appears to have no impact on the storage system so that, after an apparently effective spraying programme, the system is able to regenerate from the storage rhizomes. It is for this reason that follow-up treatments are needed.

6.4 Control of bracken should not be done without considering what vegetation might replace it. As bracken cover closes and litter accumulates, fewer plant species are able to persist. Sheep's sorrel (Rumex acetosella) is a useful indicator of whether re-vegetation by regeneration can be expected following spraying. If sheep's sorrel is absent it is likely that new vegetation cover will have to be achieved by sowing rather than regeneration.

7. Methods of bracken control

7.1 There are two main approaches to the control of bracken - physical control and chemical control.

7.2 In the autumn before any bracken control starts, disturb the litter of the bracken site by cutting or burning where access and conditions allow. This will:

8. Physical control

8.1 Physical control involves the cutting or crushing of growing fronds so that the surviving rhizomes are gradually starved. This involves a long-term approach but has the potential advantage of lower cost and is less dependant on weather conditions than chemical control. Furthermore it does not damage non-target plant species.

8.2 Rolling and cutting can easily damage sensitive archaeological sites and is a threat to ground-nesting birds. Archaeological features should be marked and these areas dealt with by hand. Where ground-nesting birds occur, either avoid treatment during the nesting and fledging period; consider other forms of bracken control or retain the stand of bracken for its value as a nesting habitat and concentrate efforts on other areas.

8.3 Physical methods of control should be the first option for small areas of bracken or light infestations, particularly as they are less likely than chemical methods to harm livestock, wildlife and non-target species.

8.4 Cultivation is effective on areas accessible to machinery and exposes the bracken rhizomes to winter frost. It is only appropriate where there is a shallow slope and the bracken is dense. Ploughing from late June to early August is most effective. Two passes with deep tines intersecting at right-angles have successfully controlled bracken without ploughing.

8.5 Good results can also be achieved by the short-term use of stock on areas of bracken to break up the litter, allowing frost to damage the rhizomes. Winter feeding is a vital part of this method as stock may otherwise be poisoned by eating dead bracken or rhizomes. Bracken is also sensitive to trampling during early periods of frond growth, however stock may need to be moved in the spring to stop them eating young bracken. Control by trampling should not be used where nearby vegetation, such as heather, is sensitive to trampling.

8.6 Bracken cutting should be targeted at more mature fronds which should be cut twice a year, about mid-June and again six weeks later. This will need to be done for at least three successive years.

8.7 Crushing with a roller is less effective than cutting, but is useful on difficult terrain
and as a follow-up treatment on sprayed areas. Crushing is best carried out during early frond growth while the stems are still brittle. Crushing should be done twice a year for three years, or once a year for five years.

8.8 Where ground-nesting birds such as nightjar occur in bracken, cutting and crushing should be timed to avoid the nesting and fledging period.

8.9 Burning bracken litter may be helpful in providing access; to ease cultivation and to encourage the subsequent germination and establishment of grass. It serves no direct control purpose in itself, although autumn burning may help with penetration of frosts to the rhizome. A Muirburn Code includes other valuable information on burning in upland areas. Where muirbum takes place in bracken, experience has shown that there may be two consequences. Either the bracken will invade the heather area in the absence of competition, or the heather will establish on the bracken site, helped by the removal of litter and exposure of rhizomes to frost damage.

8.10 Establishing tree-cover can, in the long term, suppress bracken growth by shading. The initial establishment of trees may be difficult in competition with bracken, but weed control is an important part of most woodland establishment.

9. Chemical control

9.1 Chemical control is with either asulam, (sold as Asulox) or glyphosate (generally sold as Roundup). Both are translocated herbicides. Asulam is preferable, being more specific and cheaper, so it is used more widely than glyphosate.

9.2 Compared with most herbicides, asulam is reasonably specific, principally killing ferns. However, some effects of asulam have been noted in non-target species including lesser spearwort, bird's-foot trefoil, greater bird's-foot trefoil, bog pondweed, marsh thistle, species of saxifrage, a range of grasses and some rush species. Avoid spraying near rare ferns or, if necessary, spot-treat carefully with a knapsack sprayer.

9.3 Glyphosate is a broad-spectrum herbicide affecting most forms of vegetation and should not be used where it may affect any non-target species. It is really only suitable where other vegetation is not present, for example in tracts of dense bracken with a thick litter and no understorey of grass, heather etc., and even then it must be used with great care to avoid drift.

9.4 Glyphosate has the advantages of a wider window of application than asulam and it produces browning symptoms, so that the even-ness of application can be judged in the year of spraying.

9.5 Glyphosate can only be applied by knapsack sprayer, tractor sprayer or weed wiper. It is not approved for aerial application.

9.6 Timing is important for effective results. To ensure maximum absorption and translocation to the rhizome, bracken should be sprayed when the fronds are fully expanded and bright green, and before any die-back occurs. This is usually mid-July to late August, depending on the altitude and season. Rain within 24 hours of spraying will reduce effectiveness.

9.7 There is a range of application methods to suit the location and scale of the treatment required. These are outlined below.

9.8 Tractor-mounted sprayers.

9.9 Aerial application (usually by helicopter)

9.10 Knapsack sprayer

9.11 Ultra-low volume drift spraying is another option, though this requires a steady wind of 5-25 km/hr and the bracken has to be walked through at a very slow pace. There is a danger of drift causing under-application on the target area as well as effects on adjacent, non-target sites. When using ultra-low volume equipment on or near conservation sites, a 100m buffer zone should be used to protect sensitive areas.

9.12 Do not cut grass or admit stock for 14 days after spraying bracken.

9.13 Weed wipers

9.14 Landowners using herbicide for the control of bracken in Scotland should notify the following bodies prior to application (other authorities apply in Wales, N. Ireland and England):

9.15 The use of pesticides is regulated by the legislation listed below. During all operations involving pesticide use the regulations governing supply, storage and use of pesticides should be complied with. These include:

9.16 Since January 1989 a Certificate of Competence in the Use of Pesticides is required by all users of agrochemicals, unless the operator was born before 1 January 1965 and uses the chemical only on his own land and does not supervise others in the use of pesticides. When using a herbicide always read and follow instructions on the label.

10. Follow-up management

10.1 Without effective aftercare, bracken will stage a rapid come-back. Regenerating fronds or areas missed during initial control must be brought under control.

10.2 Follow-up may be by chemical or physical control, and a combination of different methods can be beneficial. For example, a single cut of bracken can create an even canopy, a higher density of fronds and more active buds on the rhizome. This increases the efficacy of herbicide which can then be applied in the following year.

10.3 In general, two years should be allowed between phases of spraying in order to allow dormant buds on the surviving bracken rhizomes to emerge.

10.4 As a guideline the area subjected to aerial spraying in any one season should not exceed that which can be easily covered by follow-up treatment with a knapsack sprayer or weed-wiper.

10.5 Trampling by stock can help suppress surviving fronds on sprayed areas other than
on sites sensitive to trampling, e.g. archaeological sites. Young bracken fronds growing just below the surface are particularly sensitive to treading during the spring. Cattle are more effective than sheep but potentially cause more damage to other vegetation. Stock treading also increases the rate of breakdown of dense bracken litter.

10.6 Depending on the long-term objectives, treated areas may be subsequently managed in the following ways:

10.7 In some areas vigorous heather regeneration may keep bracken in check in the future, but this effect will be hindered by stocking at too high a density, even for short periods.

11. Health and safety

11.1 Use four-wheel drive tractors with approved safety cabs or appropriate ATV equipment. Drivers should be experienced at operating machinery on steep and uneven ground.

11.2 Bracken spores are believed to be carcinogenic. Spore production may occur in some parts of the country, particularly during warm, dry conditions, but seldom in Scotland. A face-mask should be worn when working in spore-producing bracken, though bracken control generally takes place before spores are produced.

11.3 Roads, bridleways and footpaths should not be sprayed-over and warning signs may be needed to advise people to keep to rights of way. Warning signs must be put up where berries might be picked.

11.4 Springs or watercourses are often used as water supplies and are of conservation interest. These areas should not be sprayed-over.

12. Grant aid for bracken control

12.1 Grants for control of bracken are available to participants in some Environmentally Sensitive Area Schemes, in ESAs bracken control is only acceptable as part of an integrated conservation management plan and there is a presumption against aerial application (prior authorisation being required).

12.2 in the Objective 1 area, participants in the Highlands and Islands Agricultural Programme, can receive a 60% grant for bracken control.

12.3 The Forestry Authority may give a discretionary grant for 50% of the cost of bracken control where it is needed to encourage regeneration on land adjacent to, or within woodlands.

12.4 Grants may also be available from the Scottish Office Agriculture Environment and Fisheries Department (SOAEFD).

13. Further information Further reading and references


Contacts for advice and information:

Agriculture and Woodland Environments
Scottish Natural Heritage
Research and Advisory Services Directorate
2 Anderson Place
Tel. 0131-447 4784
Local Farming and Wildlife Advisory Groups (FWAG)


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