Project title: Aerial Oomycetes: Assessing Management and Control Options Needed in UK Edible & Ornamental Crops Project number: CP 157 Project leader: Erika F. Wedgwood Report: Final Review Previous report: N/A Key staff: Matthew Hamilton (ADAS) Erika Wedgwood (ADAS) Matthew Cromey (RHS) John Scrace (RHS) Geoff Denton (RHS) Celia Van Sprang (ADAS) Tim O’Neill (ADAS) Tim Pettitt (University of Worcester) Peter Gladders (ADAS) David Talbot (ADAS) Jill England (ADAS) Angela Huckle (ADAS) Sarah Mayne (ADAS) Chris Creed (ADAS) Janet Allen (ADAS) Agriculture and Horticulture Development Board 2016. All rights reserved Locations of project: ADAS UK Ltd ADAS Boxworth Battlegate Road Boxworth Cambridge CB23 4NN The Royal Horticultural Society Wisley Woking Surrey GU23 6QB University of Worcester NPARU Charles Darwin Building University of Worcester Henwick Grove Worcester WR2 6AJ Industry Representative: Karl O'Neill, Bransford Webbs, The Bransford Webbs Plant Company Bransford Worcester WR6 5JN Date project commenced: 1 October 2015 Date project completed: 31 March 2016 Agriculture and Horticulture Development Board 2016. 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All rights reserved AUTHENTICATION We declare that this work was done under our supervision according to the procedures described herein and that the report represents a true and accurate record of the results obtained. Erika Wedgwood Project Leader, ADAS Signature Date 31 March 2016 Matthew Cromey Project Collaborator, RHS Signature Date 31 March 2016 Report authorised by: Barry Mulholland Head of Horticulture, ADAS Signature Date 31 March 2016 Gerard Clover Head of Research, RHS Signature Date 31 March 2016 Agriculture and Horticulture Development Board 2016. All rights reserved CONTENTS GROWER SUMMARY ............................................................................................... 1 Headline.................................................................................................................. 1 Background ............................................................................................................. 1 Summary ................................................................................................................ 1 Host range ..................................................................................................................... 2 Biology .......................................................................................................................... 2 Integrated Crop Management ........................................................................................ 2 Financial Benefits ................................................................................................... 3 Action Points ........................................................................................................... 4 SCIENCE SECTION .................................................................................................. 7 Introduction ............................................................................................................. 7 References .................................................................................................................... 9 Aims and Objectives ............................................................................................. 11 Materials and methods ......................................................................................... 11 Life Cycles ............................................................................................................ 13 Reference ............................................................................................................. 14 Possibilities of spread of predominantly airborne oomycetes via contaminated irrigation water ...................................................................................................... 14 References ........................................................................................................... 15 Elicitors: an overview of their mode of action ........................................................ 16 Introduction ........................................................................................................... 16 Types and pathways of elicitation agents .................................................................... 16 Degree of elicitation can vary with host genotype ........................................................ 18 Potential drawbacks of elicitors ................................................................................... 19 Conclusion ............................................................................................................ 19 References ........................................................................................................... 20 Agriculture and Horticulture Development Board 2016. All rights reserved Changes affecting the incidence and severity of aerial oomycete diseases ......... 21 Fungicide resistance in aerial oomycetes and product availability ............................... 21 Invasive pathogens ..................................................................................................... 24 References ........................................................................................................... 25 Edible Crop Reviews ............................................................................................ 25 Vegetable Brassica Downy Mildew .............................................................................. 25 References ........................................................................................................... 29 Vegetable Brassica White Blister ................................................................................. 31 References ........................................................................................................... 34 Onion Downy Mildew ................................................................................................... 36 References ........................................................................................................... 38 White Tip of Leeks ....................................................................................................... 38 References ........................................................................................................... 40 Pea Downy Mildew ...................................................................................................... 41 References ........................................................................................................... 43 Broad Bean Downy Mildew .......................................................................................... 44 References ........................................................................................................... 45 Cucumber Downy Mildew ............................................................................................ 45 References ........................................................................................................... 49 Tomato Late Blight ...................................................................................................... 51 References ........................................................................................................... 54 Wild and Salad Rocket Downy Mildew ........................................................................ 55 Red Beet Downy Mildew ............................................................................................. 56 Rhubarb Downy Mildew ............................................................................................... 58 References ........................................................................................................... 59 Blackberry Downy Mildew............................................................................................ 59 References ..........................................................................................................