Bracken and the Asulam ban
Bracken is well known as an agricultural, ecological and health problem with little in the way of redeeming features. It has long been the subject of control measures, but for the last three decades these have focussed on the aerial application of a herbicide called asulam (trade name Asulox) with later ground-based follow-up treatment of regrowth. Alternatives such as cutting are possible only on a small fraction of bracken areas where vehicle access is safe and practical.
A ban on asulam use in the European Union came into effect on 31 December 2011 and all stock must be used up by 31 December 2012. Consequently the main weapon for bracken control in the armoury of land managers may be lost, though there is hope that emergency authorisations may allow for continued use.
This article explores a possible scenario following the ban on the spread of bracken by comparing the area sprayed since the chemical was licensed to the extent of bracken over the UK. In effect the analysis assumes that asulam had not been invented or licensed for aerial application.
- The total area of bracken sprayed from the air between 1978 and 2010 was 1643 km2. The area sprayed each year has remained relatively constant since 1990 at about 70 km2 per year.
- The data for area are “noisy”, but there was a significant decline between the 1998 Countryside Survey and the one done in 2007.
- Assuming that all the bracken sprayed since licensing has resulted in long-term control, then adding this figure (1643 km2) to the 2007 figure of bracken cover for GB (2600 km2) gives an estimate of the potential current extent if the spraying had never been carried out. This addition gives an area of 3897 km2, an increase of c. 50 % over the current extent of this plant. A further 346 km2 has been controlled since the last Countryside Survey in 2007, so potentially the current area of bracken would have been even higher than this estimated 3897 km2 if asulam had not been sprayed from the air as it has been.
- How much productive or valuable vegetation has been created by bracken control is unknown but Countryside Survey records losses of bracken to Acid Grassland and Dwarf Shrub Heath, and to a lesser extent Broadleaved woodland and Coniferous woodland.
- The Countryside Survey data also shows that bracken continues to invade the same habitats as it invades new areas. Asulam use has prevented that continuing spread contributing to increasing bracken extent.
Data was accessed from two sources. Firstly the data on aerial applications held in the Pesticide Usage Survey Reports was accessed for records on the aerial application of asulam. Secondly, areas of bracken recorded in the Countryside Survey were also accessed. It should be noted that the Pesticide Usage data is for the UK whilst GB data was used for bracken cover as Northern Irish data is not available for the earlier surveys. However, bracken is relatively rare in Northern Ireland and so lack of data is unlikely to alter the conclusions drawn. Also, it should be noted that the earlier Countryside Surveys had much smaller sample sizes and hence much larger errors than the more recent ones.
The data were analysed to show what would have been the impact of not treating bracken with aerial applications of asulam since 1978. The analysis assumes that all control is 100 % effective and long-term. In a long-term study on the North York Moors there was some regeneration on many sites and complete regeneration on two out of twenty. Thus this assumption is generous but it illustrates the potential effectiveness of asulam in recent years.
- This simple analysis reveals the importance of asulam to land management. Without it there would be up to 50 % more bracken in the landscape than there is now.
- Without asulam in the armoury, then potentially the best control method might be tree planting. This addresses current woodland expansion targets and bracken could be a specific target of planting or even attract a higher payment rate to emphasise the win:win nature or replacing it by trees. However, work is necessary to develop planting techniques that do not involve the asulam application often used to allow establishment.
- Many land managers will already be in agri-environment agreements that specify areas to be treated. Control of new areas may need re-negotiation as the proposed use of asulam beyond 2012 is prevented by the EC regulations, unless emergency authorisations can be routinely agreed.
- Other land managers may be in agreements where follow-up treatment is specified. Spot spraying of glyphosate is an alternative, but that means extra care is necessary to avoid impacts on other plant species.
- If asulam isn’t used then the long-term consequences for farming and conservation in the UK uplands are serious as control by aerial spraying is the only option in many areas. Specific monitoring may be needed to detect the scale of brackens impact.
Professor Robin Pakeman firstname.lastname@example.org