Weed Resistance Action Group (WRAG) - the next 25 years

Transcription

1 Aspects of Applied Biology 127, 2014 Crop Production in Southern Britain: Precision Decisions for Profitable Cropping Weed Resistance Action Group (WRAG) - the next 25 years By J H CLARKE 1 and S R MOSS 2 1 ADAS Boxworth, Boxworth, Cambridgeshire CB23 4NN, UK 2 Rothamsted Research, Harpenden, Hertfordshire AL5 2JQ, UK Corresponding Author James.Clarke@adas.co.uk Summary WRAG was established in The role and achievements of the group in helping farmers, agronomists and manufacturers are outlined. Key successes include frequent publication of management guidelines and special meetings on topical subjects. Other achievements have included warning statements on product labels and links to other relevant groups. There are a number of lessons from the first 25 years, such as needing pro-active approaches to management, consistency of message and diversity of options, which will guide relevance and activity in the next 25 years. Good communication is vital and, with increased ability to predict resistance and improved testing to optimise management, this should enable uptake of cost-effective integrated approaches. Future challenges are predicted to include continued pressure from grass-weed resistance, a higher risk of broadleaved resistance and an increased risk of development of resistance to glyphosate in arable crops, as well as in perennial crop and amenity situations. Key words: Herbicide resistance, weed management, achievement, prediction, challenge, tests, communication What is WRAG? The Weed Resistance Action Group (WRAG) is an informal and independent group of those involved in research and communication in relation to managing herbicide resistance in the UK. It receives no regular funding, although it receives in-kind support from members who provide facilities for meetings. Organisations, such as HGCA have also contributed funding for publications. WRAG was formed in There is a steering group of about 10 people comprising: representatives of the Crop Protection Association (CPA) and Agricultural Industries Confederation (AIC) member companies; and organisations involved in herbicide resistance research (e.g. ADAS UK Ltd, Rothamsted Research, Health and Safety Executive (HSE)/Chemicals Regulation Directorate (CRD), universities, colleges and Agricultural and Horticultural Development Board (AHDB- HGCA)). There are normally one or two steering group meetings per year, with communication to a wider membership of meeting minutes and topical items through an extensive ing list and through occasional open meetings. We maintain contact with other groups worldwide, such as Herbicide Resistance Action Committee (HRAC). A web site is maintained and is in the process of being revised (see references for address). The new site will include pdf versions of all WRAG s publications, as well as many research reports, and will be a key source of information on herbicide resistance in the UK. 273

2 The objectives of WRAG are: to provide a forum for information exchange between people actively involved in research into herbicide resistance; to discuss and promote strategies to avoid resistance and to manage resistant populations; to define research needs; to discuss resistance test methodologies and agree standards; to agree statements for the media, whether in response to queries or as unsolicited news releases; to maintain communication with similar groups which have been established successfully in other countries. Achievements The main output from WRAG has been publication of resistance management guidelines. The first edition was in 1991, with updates in 1993, 1997, 2003, 2008, 2010 and most recently minor updates in These have ensured consistent messages have been communicated and they are now referenced on herbicide labels as part of management guidance for products, as follows: Strains of some annual grasses (e.g. black-grass, wild-oats and Italian rye-grass) have developed resistance to herbicides which may lead to poor control. A strategy for preventing and managing resistance should be adopted. Guidelines have been produced by the Weed Resistance Action Group and copies are available from the HGCA, CPA, your distributor, crop advisor or product manufacturer. Other publications include a grass-weed resistance audit and spreadsheet (2004), 10 facts (2005), herbicide resistance in amenity situations (2009) and the benefits of herbicide resistance testing (2012). All are available from the WRAG website (see references for link). A range of meetings have been held on specific topics with industry-wide involvement. The focus in the early years of the group had been on grass-weeds. In 1998, a meeting was held to consider the threat of resistance in broad-leaved weeds. The meeting culminated with attendees being asked to predict the likely incidence of resistance by Some of the 20 attendees were very close in their predictions, others less so. Compared with the 2008 guidelines, the key species were anticipated well although numbers were less than many feared. It was interesting to note that research based attendees predicted lower, and more accurate, numbers than those from industry. A meeting took place in 2005 to examine the evidence for herbicide resistance associated with ACCase and ALS inhibitor herbicide use on grass-weeds. One outcome of that meeting was the Advisory Committee on Pesticides (ACP) publishing a position paper on sequences and mixtures and the need for applicants to assess risk prior to approval with restrictions introduced on the frequency of use of ACCase and ALS inhibiting herbicides. The paper led to Efficacy Guideline No. 611 (HSE, 2007) in which a specific restriction To avoid the build up of resistance do not apply this or any other product containing an ALS inhibitor herbicide with claims for control of grass-weeds more than once to any crop precluded a sequence of two ALS inhibitor herbicides with activity on grass weeds. Any applications for approval of mixtures and sequences of ALS inhibitor herbicides with grass weed activity must now also provide a resistance risk assessment for that sequence. An outcome of a 2007 meeting was production of a note on the implications of the loss of trifluralin in the UK. More recently a meeting in 2014 has considered the potential risk of glyphosate resistance in the UK. WRAG has also been active on a number of initiatives which include compilations of numbers of cases of resistance (in 1989, 1991, 1994, 1999, 2007, 2011, 2014 (Hull et al., 2014)) and this has informed updates of the UK position on the HRAC-funded international survey of herbicide resistant weeds ( The resistance test methodology has been evolved and WRAG has been pro-active in how results are presented, such as introduction of the 'R' resistance rating system (Moss et al., 2007). This system assigns populations to four categories, S (susceptible), R? (marginally resistant), RR (resistant), RRR (highly resistant), depending on the degree of resistance 274

3 relative to a susceptible standard. We believe we are one of very few countries globally to have a standardised method of assigning resistance accepted by all agrochemical companies as well as researchers. In 1997 the need for improved approaches and consistency was highlighted through a 'ring' test. Other discussions have resulted in the recognition of the importance of providing mode of action information and associated resistance warnings in product literature. We have also considered options for baseline sensitivity testing and interpretation. We maintain links with other resistance action groups in the UK (such as on FRAG (fungicides), IRAG (insecticides) and RRAG (rodenticides)), and other relevant organisations in Europe (e.g. EPPO) and worldwide (e.g. HRAC). Lessons WRAG activity and experience has provided many lessons on the challenges of resistance development and communication of management information. One major lesson is the need for a pro-active approach to resistance management and stewardship. This needs to be reinforced by consistency of messaging from multiple sources. Organisations with an independent and evidence based approach can help determine these and make messages available to those interacting with regulators and farmers to help enable better adoption of critical actions. It is important that these messages are practical and as clear as possible and that regulatory approaches and advice support each other. The ability to manage resistance effectively has depended on a diversity of available options and is enhanced by an ability to predict any likely resistance development (especially in identifying cases where resistance will not develop). This helps ensure that risk is effectively assessed and appropriate management is recommended and deployed. The targeting of appropriate strategies have been aided by effective test methodology and clear reporting. Our ability to detect resistance early has been demonstrated on many occasions; it is typically the uptake of relevant management practices to reduce development that have been slower to be adopted. This reflects the cost-effectiveness of options and priority farmers and agronomists give to resistance management in decision making. Challenges Worldwide, no new modes of action have been marketed for over 20 years (Duke, 2012), which is why herbicide resistance poses a continuing and major threat (Heap, 2014). It is widely agreed that there will be continued and increasing demand for crops and pressure on management of the cropped area. Management of land will increasingly be in larger units and hence messages and tools for resistance management need to be appropriate to these situations. Effective management of herbicide-resistance depends on having a diversity of management options available. This needs to include both herbicide and cultural options which can be deployed in an integrated way. There is increasing difficulty in finding effective herbicides which also cause little or no risk to water quality and few new modes of action are in development, or likely (as reported by companies). The most recent new modes of action have posed high resistance challenges, which require careful stewardship to ensure long-term effectiveness. Authorisations tend to be with restricted timing and/or rates of use. Despite this there will be development of other helpful technologies, many of which we cannot yet predict! In the next 25 years there will be a complimentary role of regulation alongside advice and stewardship. There is a limit as to what can be included on a product label and so supporting advice is critical in ensuring effective use. A key impact will be in how EU Directive 1107/2009 and in particular how substitution affects availability of products (and any restrictions on their use). There will need to be relevant management at a farm or field specific level to ensure effective use and outcomes. To do this effectively will require continued communication of the latest research findings and a particular focus should be on how to provide farmers and agronomists with improved ability to allow them to initiate changed strategies for weed control when they need to. This requires a combination of improved biological risk predictions with improved monitoring so that early detection of low levels of resistance can provide a trigger for management change. 275

4 WRAG will also need to be attentive to new resistance challenges. With no new modes of action and increasing resistance to post-emergence herbicides, there will be greater selection pressure on pre-emergence herbicides used for grass-weed control, especially in black-grass (Alopecurus myosuroides). Control of wild-oats (Avena spp.) is very dependent on the high resistance risk ACCase and ALS inhibiting herbicides, and few effective non-chemical options are available, so this threat needs monitoring and addressing. There is also likely to be increased risk of resistance to ALS inhibitor herbicides in broad-leaved weeds. Maintaining a range of other modes of action will be critical to ensuring control can be achieved in species where typically there are more limited opportunities to supplement chemical control with cultural options. Resistance is also likely to evolve in new species. Which species will depend on what chemistry is available, but charlock (Sinapis arvensis) is one species we predict to be at risk of developing resistance. In addition, there may be certain specific challenges related to specific changes. For instance if the intensity of spring cropping increases, spring germinating weeds such as fat-hen (Chenopodium album) would be exposed to greater herbicide pressures. Although we are not currently aware of any likely changes to product availability, cleavers (Galium aparine) control is very dependent on herbicides. If some of these became restricted or unavailable it would increase resistance risk. The other major emerging challenge, which we have already started to address, is glyphosate resistance. Currently, in the UK, we have no species with resistance to glyphosate and the few cases elsewhere in Europe are mainly in perennial crops, such as orchards and vineyards. However, the first case of a glyphosate-resistant weed (Lolium spp. in Italy) in a European annual arable cropping system has recently been reported (Collavo & Satin, 2014). In UK situations vigilance and relevant strategies are required in several specific situations. Field crops often receive several applications pre-sowing and there is increasing interest in applying glyphosate between crops grown in rows. With field crops increasingly receiving multiple applications this creates multiple selection potential. When accompanied by cultivation this risk is reduced, but with pressure to reduce the amount of tillage for soil and energy conservation reasons, there needs to be careful monitoring to detect and prevent problems. Other multiple glyphosate applications, in conjunction with no cultivation, occur in perennial crops and also in amenity and industrial situations, such as on hard standing, and along road and rail networks. These present high potential selection pressures and need careful monitoring. In some amenity situations this is harder as different operators will be returning each time certain locations are treated. Summary We believe that the creation of WRAG 25 years ago, following a meeting initiated by George Cussans, its first Chairman, was excellent foresight. WRAG can be proud that it was the catalyst for the subsequent formation of the other RAGs (FRAG, IRAG, RRAG) in the UK. These have provided a central point of evidence based information made available and relevant to the whole industry. In the next 25 years there will be increased need for this activity. The evidence that WRAG has used in its activities comes from topical, applied research with clear outcomes and it is essential that such research continues. The structure WRAG provides gives a vehicle for ensuring future resistance issues are identified and managed. To do this the membership will need to evolve and there will need to be new meetings on relevant topics. To ensure this success continues, we must build on the three core principles under which WRAG has operated for the last 25 years, namely: be independent; ensure consistency of messages; be pro-active. 276

5 Acknowledgements We would like to thank HSE (CRD) & Defra, HGCA, steering group members, previous chairmen (George Cussans, Jim Orson) and many farmers and agronomists for their valuable input to WRAG over the last 25 years. Rothamsted Research is a national institute of bioscience strategically funded by the Biotechnology and Biological Sciences Research Council of the United Kingdom. References Collavo A, Sattin M First glyphosate-resistant Lolium spp. biotype found in a European annual arable cropping system also affected by ACCase and ALS resistance. Weed Research 54: Duke S O Why have no new herbicide modes of action appeared in recent years? Pest Management Science 68: Heap I Global perspective of herbicide-resistant weeds. Pest Management Science 70: HSE Guidance on the Restriction of Use of High Resistance Risk Herbicides ( pesticides.gov.uk/resources/crd/migrated-resources/documents/e/efficacy_guideline_611. pdf). Hull R, Tatnell L V, Cook S K, Moss S R Current status of herbicide-resistant weeds in the UK. Aspects of Applied Biology 127, Crop Production in Southern Britain: Precision Decisions for Profitable Cropping, pp Moss S R, Perryman S A M, Tatnell L V Managing herbicide-resistant black-grass (Alopecurus myosuroides): Theory and practice. Weed Technology 21: WRAG website: Resistance-Action-Groups/wrag. 277

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