BCPC Weed Review highlights challenges ahead for herbicides

Over sixty delegates attended the 48th BCPC Annual Weed Review chaired by Dr Gordon-Anderson-Taylor, Bayer CropScience, and held at PGRO, Peterborough on 9 November. The Review addressed a wide range of issues affecting weed control in the UK today.

Dr Ruth Mann from STRI highlighted a number of problems facing the amenity sector particularly in the sports turf area. Golf courses aim for an even playing surface. In particular annual meadow-grass on greens is a major issue since it contributes to thatch build-up, and also moss and disease problems. Certain broad-leaved weeds occur in different conditions e.g. yarrow in dry conditions; buttercup in wet conditions; daisies where there has been close mowing and plantains where there is compaction. Cultural control measures will improve conditions whilst MCPA, dicamba, clopyralid and fluroxypyr will offer broad-leaved weed control. Although perennial ryegrass control can be achieved with pinoxaden, a selective for effective annual meadow-grass control in turf is still proving elusive.

Grass weeds are one of the biggest weed control challenges in arable crops – the vertical nature of these weeds means that the target area is more difficult to hit with sprays. In her presentation, Dr Clare Butler-Ellis from NIAB/TAG outlined recent advances in application that offer improved weed control especially on grass weeds. Getting a good deposition on a vertical target can be achieved by a slight wind, a forward speed and angling nozzles forward to give the droplets a horizontal velocity. The effect of volume is also important – surprisingly, higher volumes reduce the quantity of active ingredients impacting on the grass weed target in cereal canopies. There seems to be no advantage in applying more than 100l/ha.

EU pesticide legislation and Directives continue to hit the headlines and Ingrid den Hoed from CRD highlighted the impact it was having on the availability of herbicides. 74% of actives have been lost under EU91/414 with 67% removed from the market and a further 7% not approved after review. The EU Thematic Strategy now offers, for the first time, legislation and directives that cover all stages of the pesticide life cycle, including pre-marketing authorisation 1107/2009 to replace 91/414; the use stage including the Sustainable Use Directive and Post-use monitoring with the Water Framework Directive (WFD). The potential impact of greater reliance on fewer actives includes the increased likelihood of resistance developing. Grass and broad-leaved weed control – especially in oilseed rape – will become increasingly difficult. New solutions need to be found, both chemical and non-chemical, and a more whole farm integrated approach to crop production adopted.

A key impact of losing herbicides is the cost the industry. Sarah Wynn, Farm Systems Consultant, ADAS explained that where there are black-grass problems, oilseed rape yields could be reduced by up to 1.2t/ha due to loss from competition and increased herbicide costs resulting in £390/ha lost in gross margin. If glyphosate were to be lost severe financial losses to UK agriculture would result, especially in pre-planting use. Without glyphosate (vulnerable under the WFD), the loss of gross margin in wheat production in the UK could be up to 17%, oats up to 20% and oilseed rape up to 15%.

Environmental stewardship (ES) herbicide choice is getting smaller and as a result this is affecting farmers’ willingness to take up ELS and particularly HLS, explained Mike Green from Natural England. Grass weeds are a particular problem in, for example, wildflower margins in HLS schemes and new EU pesticide legislation is likely to hinder rather than help. The future focus for ES needs to be on quality rather than quantity of sites driven by support and guidance rather than further restrictions.