Bracken control, vegetation restoration and land management
Bracken control, vegetation restoration and land management
The information in this advice note is based on the findings of long term research programme funded by Defra. It summarises the agricultural and environmental problems associated with bracken (Pteridium aquilinum) as well of some of the environmental benefits that it can bring. It goes on to provide guidance on where and when bracken can be controlled, as well as when it is inadvisable to do so. Mechanical and chemical methods of control are explained for scenarios where bracken stands are commonly found. Options and methods for the establishment of more desirable vegetation in these scenarios are also given. Summary guidance on the health and safety aspects of control and restoration is also given
RDS TAN 1? - Published December 2002? / 5Bracken control, vegetation restoration and land management
Introduction
Bracken is a very successful plant. It is vigorous and an aggressive competitor. It invades lowland grassland and heathland and upland grazing and heather moorland: it can persist in shady woodlands and hedgerows from which it can colonise neighbouring open areas. Its presence can prevent satisfactory shepherding and, if eaten, can cause poisoning in grazing animals: It is a favoured haunt of the sheep tick (Ixodes ricinus), which can carry Lyme disease. Bracken also has a major impact on archaeological remains. It may disturb and destroy below-ground archaeological deposits, obscure archaeological sites, thereby reducing their visibility and making them more vulnerable to inadvertent damage.
Bracken can also bring certain benefits. In some areas there may be associations between bracken and some fritillary butterflies in western Britain. Moreover, some birds such as whinchat and nightjar use bracken as their preferred habitats. Bracken also brings structure and colour to the landscape.
Controlling bracken should result in increased herbage production and more valuable vegetation from a conservation viewpoint. It may also improve labour efficiency, the health of grazing animals, and stabilise the condition and improve the visibility of archaeological sites. Grants for control are available under the ESA and Countryside Stewardship schemes.
Factors to consider
There are several important messages that anyone considering bracken control must consider:
· Complete eradication must be viewed as a long-term goal, which may be inappropriate in some cases.
· If bracken is to be maintained at a low level then control treatments are essential on a continuing basis.
· The best and most cost-effective results will come from treating stands that still possess some ground vegetation.
· There is no point in controlling dense bracken without considering the vegetation that is to replace it.
· The need to plan areas of control to minimise adverse effects on landscape quality, by avoiding rectangular blocks and working in irregular patches with boundaries against natural features.
· Whether it is more acceptable to manage for woodland (by planting or natural succession) on sites with limited agricultural potential or environmental value.
· The need to evaluate the extent of any archaeological remains and the ability to effectively eradicate and maintain a bracken-free environment. This may require advice from an archaeologist.
This leaflet aims to guide the land manager through a range of potential bracken scenarios so that the most suitable options can be chosen. Before embarking on a bracken control programme it is important to identify clear goals of what is to be achieved and the problems likely to be encountered. Scenarios 1 and 2 describe the strategies necessary to control bracken where a good vegetation cover is present (Table 1), whilst scenarios 3 and 4 should be followed when controlling bracken with little other vegetation present. Table 1 illustrates some of the pros and cons of the different approaches to bracken control and the subsequent use of the land and should help to devise suitable methods of treatment for most situations. The costings presented are for outside contractors, and would be considerably less if carried out as part of normal land management operations.
Do not control where:
· the long-term costs exceed the likely environmental and/or agricultural benefits;
· bracken occurs on steep slopes which may be subject to erosion whilst without vegetation;
· a woodland ground flora (e.g. bluebells and wood anemones) is present beneath the canopy; in S.W. and N.W. England in particular, avoid areas with violets or cow-wheat beneath the canopy, as these may be important for fritillary butterflies;
· other ferns are present or occur nearby, where they may be damaged by drifting spray; care should be taken near rocky areas and upland watercourses that harbour many ferns; and where
· control may result in the damage of archaeological features if inappropriate methods are used..
Methods of bracken control
Control should be seen as a two-stage process. An initial stage where treatments suitable for large-scale use are employed to reduce the cover of bracken and open up the stand for revegetation treatments or grazing where appropriate. The second stage entails the use of either 1) intensive follow-up treatments aimed at eradication, or 2) less intensive treatment aimed at maintaining bracken at low levels. It should be stressed that both of the latter strategies need the appropriate commitment of resources to ensure success and this should be considered carefully before embarking on a control programme.
Mechanical methods
Ploughing and cultivation
On areas that are not too steep or rocky a good reduction in bracken cover can be achieved by ploughing between late June and early August. Aim to invert deep furrows to expose the bracken rhizomes; leave undisturbed over winter and follow with spring sowing. Deep tine cultivation in two directions has successfully controlled bracken without ploughing. Some regeneration will occur, so a follow-up program using another method must be employed. This method should not be used on sites with a valuable ground flora or with archaeological remains.
Cutting
Cut twice each season, about mid-June when the bracken is 50-75cm high (this cut may have to be later in the uplands) and again six weeks later. Repeat this for at least three years. If only one cut is possible, take it in late July and repeat for at least five years. The two-cut system allows earlier access to vegetation under the bracken by grazing stock. Cutting will need to be repeated if the bracken shows signs of recovery. Complete eradication will not be achieved by this method – follow-up will be necessary by some other means to achieve this. These methods should not be used where ground-nesting birds are present or on sensitive archaeological sites where the use of hand-held strimmers should be considered.
Crushing
This is less effective than cutting, but is suitable for difficult terrain which might damage a cutter. It is usually best carried out repeatedly on young fronds that are brittle and easily snapped. Repeat the treatment for at least three consecutive years if two crushings are done and five years if only crushed once annually. The technique is useful as a follow-up treatment on a sprayed area. Use a flat or Cambridge roller. Special bracken crushing rollers fitted with deep cross-ribs (e.g. Cuthbertson, Holt) may be available locally. Repeat if the bracken shows signs of recovery. Like cutting this method is unsuitable for eradicating bracken and follow-up by other means is necessary. There is a risk of erosion if this method is used on sloping ground. It should not be used where ground- nesting birds are present or on sensitive archaeological sites where the use of hand-held strimmers should be considered.
Stock treading
Winter-feeding can be used to attract livestock on to the site so that, 1) bracken buds and developing fronds which are close to the surface or just emerged are damaged by stock treading (cattle are more effective than sheep) and 2) the litter is disturbed and broken up (this also encourages frost penetration to the rhizomes. In spring, as new fronds expand remove stock, to prevent poisoning. This is not a reliable method but can help damage surviving fronds as a follow-up on sprayed areas. It should not be used where the vegetation is easily damaged by trampling (e.g. heather), where particularly vulnerable archaeological deposits are located or where unsightly fencing has to be erected.
Burning
Burning of bracken litter is useful to ease cultivation and seeding success. Burning of dead litter without follow-up is of no benefit, constitutes an unnecessary fire risk, may increase frond production and has adverse, though temporary effects on landscape value. It is controlled by the Heather and Grass etc. (Burning) Regulations 1986 (SI 1986 No 428) as amended by the Heather and Grass Etc. (Burning) (Amendment) Regulations 1987 (SI 1987 No 1208) made under Section 20 of the Hill Farming Act 1985.
Herbicidal control
Only asulam (Asulox) and glyphosate (many formulations) have label recommendations. Recommended doses for overall application are: Asulox 11 litres/ha (cost about £74/ha); Glyphosate 5 litres/ha (about £35/ha).
Asulam can be sprayed in all densities of bracken since it has little permanent effect on underlying vegetation (other ferns excepted). In addition it is approved for aerial application. Despite being cheaper, glyphosate should only be sprayed in areas of deep litter bracken with little underlying vegetation: it will kill any grass or heather present. Modern weed-wiping machinery can be used to extend the selective use of glyphosate. Stock should be excluded from treated areas until after senescence to reduce the risk of bracken poisoning.
Both chemicals have to be applied after full frond expansion has occurred but before any die-back of the tips to ensure maximum absorption and translocation into the below- ground rhizome system. This period occurs between mid-July and late September depending on altitude, locality and season. Both chemicals can give over 90 per cent control in the year following treatment. An advantage of glyphosate is that it does produce visible symptoms soon after application, allowing treatment of missed strips in the same season. In all cases, the spot treatment of missed areas in the same season or in the following year, and the treatment of regenerating areas will considerably increase the period of effective control.
It must be stressed that bracken will regenerate after herbicide application, so further treatments will be necessary to maintain control or progress to eradication. Repeat spraying on a 5 to 7 year cycle (i.e. when recovery may have produced a complete canopy) is not effective at controlling bracken on a long-term basis.
For eradication of bracken, follow-up spot treatment should be applied annually without respite to all regrowing fronds.
Herbicide application methods
Tractor mounted machines
The booms must be set high enough for even coverage of the fronds. The area to be controlled should be walked over the previous winter to mark dangerous obstacles. This method should not be used in the vicinity of sensitive archaeological sites.
Aerial application (by helicopter only)
Only asulam is approved for this use, and spraying costs upwards of £160/hectare (including chemicals). Control by aerial spraying is likely to be most successful where there are large areas of uninterrupted bracken. Where there are obstacles that prevent a constant flying height, control will be poor. As a guideline the area to be treated annually should not exceed the area that can be comfortably subjected to follow-up treatment.
Knapsack spraying
This is useful for small areas but is tiring due to the weight of water carried, the need for frequent refilling and the effort of keeping the boom above the fronds. The method is suitable for archaeological sites and for follow-up treatment on limited areas.
Low volume drift spraying with the Micron Ulva
These are very comfortable and easy to use but bracken control is less reliable than the spray methods. There must be a steady wind of 5 to 10 km per hour over the area to be treated. Asulox is used in mixture with Adder or Actipron.
Weed wipers
Generally, ATV or tractor-mounted rotating pressurised systems. Glyphosate only is approved for use in wipers, normally at 1:1 dilution with water. The cost of application (c. £55/ha) depends on the amount of chemical used, which in turn depends on the thickness of the bracken stand.
Spot treatment
This approach can be used to control missed areas, fronds of recovering bracken after an overall spray, or patches that are inaccessible or otherwise unsuitable for tractor mounted equipment. Both asulam and glyphosate are recommended. They should both be applied to wet the foliage thoroughly, but not to the point of run-off. Spot-guns and hose and lance on ATV/quad are the most suitable methods for application.
Mixed herbicide/mechanical methods
A combination of mechanical methods and herbicide application can combine the advantages of both systems. For instance, a single aerial spray will give good control that can be maintained by regular cutting. Cutting alone may not have been safe in the previously dense bracken.
A single cut in the year before spraying produces an even canopy, a higher density of fronds and more active buds on the rhizome: all of which increase the efficacy of the herbicide. However, this is only an option on sites with easy and safe tractor access.