New strategies to maintain autumn grass-weed control in cereals and oilseed rape

Abstract

Effective grass weed control is essential if rotations of mainly autumn-sown crops are to be maintained. In future scenarios greater reliance will be placed on fewer herbicides due to increasing herbicide resistance, the absence of any new modes of action and the potential loss of key herbicides arising through the Water Framework Directive and other EU legislation. New weed control strategies need to focus on herbicides that are applied pre- or early post-emergence. The immediate concern that the Industry faces is therefore maintaining effective strategies based on remaining herbicides, but avoiding exacerbating resistance or pollution issues. This research project has ostensibly developed approaches to ‘stacking’ (applying more than one active ingredient or herbicide product at the same time) and ‘sequencing’ (when different active ingredients or mixtures of active ingredients are applied in close succession) techniques to deliver effective grass weed control and make best use of the options available. Research has specifically addressed the control of black-grass (Alopecurus myosuroides) and barren (sterile) brome (Anisantha sterilis) in cereals, black-grass in oilseed rape and annual meadow-grass (Poa annua) in cereals. With regard to the management of black-grass in winter wheat this has been done without the use of iodosulfuron-methyl-sodium + mesosulfuron-methyl (Atlantis, Bayer CropScience) where grass weed resistance is a developing issue. Research has developed approaches suited to a range of scenarios. Considering black-grass in oilseed rape findings highlight the continued importance of propyzamide and carbetamide and outline routes to help maximise their performance. Considering grass weed control in cereal crops, several active ingredients remain key to managing both barren brome and black-grass, notably flufenacet but also prosulfocarb and tri-allate (several other active ingredients have also delivered useful contributions to ‘stack’ and ‘sequence’ approaches). Data suggests that ‘stack’ and ‘sequence’ approaches can improve the robustness of the weed control strategies; with generally at least 3 active ingredients being needed in the more successful approaches. For barren brome control in winter wheat, particularly in high pressure situations, a robust programme involving a residual herbicide and ALS inhibitor (i.e. herbicides targeting the acetolactate synthase (ALS) enzyme) components is likely to be required. Research considering black-grass in cereals has developed a series of stacking and sequencing approaches however, data suggests where populations in untreated plots exceed approximately 100 heads m-2 control offered through stacking and sequencing approaches is unlikely to offer >95% reductions in black-grass heads. In all scenarios, where grass weed populations are high non-chemical management practices should also be considered.