Information and Advisory Note Number 24 Back to menu
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
2.1 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.
3.1 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
4.1 Bracken control is appropriate in the following circumstances.
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.
6.1 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.
7.1 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:
8.1 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.
9.1 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.
10.1 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.
11.1 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.
12.1 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).
Agriculture and Woodland Environments
Branch
Scottish Natural Heritage
Research and Advisory Services Directorate
2 Anderson Place
Edinburgh
EH6 5NP
Tel. 0131-447 4784
Local Farming and Wildlife Advisory Groups (FWAG)