April 2019 Research Review No. CP 182 / 1807258 Weed control options and future opportunities for UK crops Authors: Sarah K. Cook, Laura R. Davies, Frances Pickering, Lynn V. Tatnell, Angela Huckle, Sonia Newman, Chloe Whiteside, Charlotte White, David Talbot, Helen Holmes (ADAS), Patricia E. Turnbull (Independent agronomist), Denis C. Buckley (Independent agronomist), Jim Scrimshaw (PGRO) and Pamela Chambers (UPL) Editors: James H Clarke, Steve Ellis and Sarah Clarke (ADAS Boxworth, Boxworth, Cambs CB23 4NN) This review was produced as the final report of a four month project (CP 182 / 1807258) that started in September 2018. The work was funded under a contract of £26,000 from AHDB and £10,000 from BBRO, with additional funding from BASF, Bayer CropScience, Belchim, Corteva Agriscience, FMC Agro Ltd, Syngenta and UPL Europe Ltd. Additional in-kind funders and contributors: Frontier, Garford Farm Machinery, Hutchinsons, Maize Growers Association, PGRO, Procam and Rootwave. While the Agriculture and Horticulture Development Board seeks to ensure that the information contained within this document is accurate at the time of printing, no warranty is given in respect thereof and, to the maximum extent permitted by law, the Agriculture and Horticulture Development Board accepts no liability for loss, damage or injury howsoever caused (including that caused by negligence) or suffered directly or indirectly in relation to information and opinions contained in or omitted from this document. Reference herein to trade names and proprietary products without stating that they are protected does not imply that they may be regarded as unprotected and thus free for general use. No endorsement of named products is intended, nor is any criticism implied of other alternative, but unnamed, products. iii iv v CONTENTS 1. ABSTRACT .......................................................................................................................1 2. INTRODUCTION ...............................................................................................................7 2.1. Document structure ........................................................................................... 10 3. WEED CONTROL TECHNIQUES ................................................................................... 12 3.1. Integrated weed management ........................................................................... 14 3.2. Cultural Control .................................................................................................. 16 3.2.1. Rotations ....................................................................................................... 16 3.2.2. Rotational livestock grazing and weed management ..................................... 18 3.2.3. Crop species.................................................................................................. 19 3.2.4. Crop cultivars ................................................................................................. 20 3.2.5. Tillage and cultivations .................................................................................. 20 3.2.6. Fallow ............................................................................................................ 27 3.2.7. Cover cropping .............................................................................................. 30 3.2.8. Intercropping or companion cropping ............................................................. 32 3.2.9. Seed rates ..................................................................................................... 33 3.2.10. Row widths .................................................................................................... 33 3.2.11. Drilling dates .................................................................................................. 34 3.2.12. Timing of nitrogen .......................................................................................... 34 3.3. Non-Chemical Control ........................................................................................ 35 3.3.1. Manual removal of weeds .............................................................................. 35 3.3.2. Mechanical weeding ...................................................................................... 36 3.3.3. Mowing and cutting ........................................................................................ 40 3.3.4. Thermal weeding ........................................................................................... 43 3.3.5. Abrasive weeding .......................................................................................... 48 3.3.6. Mulching (excluding living plant ground cover) ............................................... 49 3.3.7. Allelopathy ..................................................................................................... 50 3.3.8. Biological control ........................................................................................... 52 3.3.9. Harvest weed seed control ............................................................................ 53 vi 3.4. Chemical Control ................................................................................................ 54 3.4.1. Existing chemistries ....................................................................................... 56 3.4.2. Current uses of glyphosate ............................................................................ 60 3.4.3. Alternatives to glyphosate .............................................................................. 60 3.4.4. Crop desiccation ............................................................................................ 62 3.4.5. Optimising use of existing chemistry .............................................................. 63 3.4.6. New chemistry ............................................................................................... 69 3.4.7. Herbicide resistance ...................................................................................... 71 3.4.8. Herbicide resistance diagnostics .................................................................... 74 3.4.9. Bioherbicides ................................................................................................. 78 3.4.10. Biopesticides – transferable technology ......................................................... 80 3.5. Novel and Emerging Technologies ................................................................... 80 3.5.1. Sensing and predicting the need for control ................................................... 80 3.5.2. Tools used to provide control ......................................................................... 83 3.6. Digital tools ......................................................................................................... 85 3.6.1. Prediction modelling ...................................................................................... 86 3.6.2. Decision support systems .............................................................................. 87 3.6.3. Internet tools .................................................................................................. 89 3.6.4. Apps .............................................................................................................. 91 3.7. Genetic Tools ...................................................................................................... 92 3.7.1. Herbicide tolerant crops ................................................................................. 92 3.7.2. Genetically modified crops ............................................................................. 93 3.7.3. CRISPR technology ....................................................................................... 99 3.7.4. RNA interference technology ....................................................................... 100 3.7.5. Quantitative trait loci .................................................................................... 100 3.7.6. Weed genome sequencing .......................................................................... 101 3.8. Preventative weed control ............................................................................... 101 3.8.1. Contaminated straw ..................................................................................... 102 3.8.2. Forage, feed and livestock ........................................................................... 102 vii 3.8.3. Composting, anaerobic digestion, and sewage sludge ................................ 103 3.8.4. Weeds in sown seed .................................................................................... 103 3.8.5. Manage weeds in non-cropped areas .......................................................... 105 3.8.6. Machinery .................................................................................................... 105 3.8.7. Water ........................................................................................................... 105 3.8.8. Predation ..................................................................................................... 105 4. THE APPLICABILITY OF WEED CONTROL OPTIONS BY CROP .............................. 106 4.1. Horticulture ....................................................................................................... 106 4.1.1. Field vegetables .......................................................................................... 106 4.1.2. Soft fruit ......................................................................................................