01 Feb 2012
Bracken is a problem for livestock farmers in many parts of the UK. It reduces grassland productivity by spreading and shading other vegetation, makes gathering of sheep flocks difficult and harbours parasitic ticks. It can also be toxic to livestock if they consume it, causing vitamin deficiencies and cancer.
Farmers mainly use a herbicide for limiting bracken, but now this method of controlling the vegetation is in doubt. Asulam - the most commonly-used herbicide - has had its approval
removed by the European Commission. From 31 December 2011, the chemical was banned across Europe, although existing stocks can be used until 31 December 2012.
Re-registration of the product – if achievable – would take until about 2016, though there is the possibility of short-term emergency authorisations that could cover the summer
period each year. Thus there is considerable uncertainty over the future of bracken limitation, creating a pressing problem for land managers who have signed up to long-term management plans under agri-environment schemes.
According to the Countryside Survey of 2007, about 1.1% of the UK (263,000ha) is dominated by bracken. It is more common in the wetter west and is a feature of hill slopes on acidic
soil. Half of the bracken in the UK is in Scotland (132,000ha).
Bracken coverage had begun to decline in the UK, with a significant reduction in Wales from 1998 to 2007. The loss was partly due to effective control, converting bracken-dominated areas into acidic grassland or upland heathland. Planting cleared bracken areas with confiers and broadleaved trees has also helped the decline.
Bracken continues to pose day-to-day management problems for livestock farmers in many parts of the UK. It has a direct impact on the productivity of land as it can shade out and completely replace other, useful, vegetation available for cattle and sheep grazing.
Bracken poses welfare issues for livestock linked to the array of chemicals it has evolved to protect itself from grazing. Cases of direct poisoning are relatively rare, but there
are risks during dry periods when grass growth is limited but the bracken canopy is still green. Long-term ingestion can lead to a range of cancers, usually associated with the oesophagus or stomach, as well as the bladder. Other problems include retinal degeneration (bright-blindness) in sheep and other vitamin deficiencies in horses and pigs, though these problems are rare.
There are some concerns about the exposure of humans to carcinogens through private water and milk supplies, but it has proved difficult to establish a definite level of risk for
Like many upland habitats, bracken also offers good habitat for ticks, which may carry Lyme disease. Lyme disease causes little overt disease in sheep (although lambs might be affected), but in dogs and humans it can affect skin, muscle, joints and nerves.
Bracken is also a problem for conservation. In rare cases it can act like a woodland canopy and preserve ground flora and butterflies, but in most situations the density of the
canopy allows bracken to spread invasively across upland grazings, grasslands and heathlands, causing a loss to species of plants and animals. In general, control is seen as a positive contribution to biodiversity.
Bracken can be a significant carbon store, meaning control can produce the negative consequence of realeasing carbon into the atmosphere. It may therefore be appropriate to replace bracken with woodland. Bracken areas should be preferred areas for planting – especially as bracken is a good indicator of former woodland.
There are two main methods available to control bracken – cutting and herbicide application. Cutting during the summer removes fronds, forces re-growth and acts by gradually exhausting the reserves in the rhizomes (root stalks) below ground. Even in summer, rhizomes can represent two-thirds of the mass of the plant, which gives some indication of how difficult it is to control. Cutting can control, but rarely will it eradicate the plant. Other mechanical methods of control such as bruising or rolling can be used, but these are all are less effective than cutting.
Herbicide application acts below ground by killing the buds that make successive years’ fronds. Best-practice is to keep applying herbicide every year to any recovering fronds.
Asulam has been the main chemical used as it has a relatively narrow spectrum, being of low toxicity to animals and to other (non-fern) plant species. It has been licensed for aerial
application by helicopter, meaning areas not accessible by tractor can be treated. Glyphosate is also licensed, but is only appropriate if there are no other plant species present and it can only be applied from a vehicle-mounted or hand sprayer.
Follow-up treatment is necessary for good control and eradication of bracken. Short-lived control is usually a sign that follow-up treatments have not been carried out properly.
Control should always be integrated with measures to establish other vegetation. In drier parts of the UK the litter below bracken is slow to decompose, so burning it or raking
it off are necessary to expose a suitable surface for sowing seeds.
Animal Briefs is an initiative by The British Society of Animal Science to provide factual and impartial information on matters of topical concern.
This brief has been prepared by Robin J Pakeman