1. Rothamsted Research; Harpenden AL5 2JQ UK
2. Department of Environment & Agriculture; Centre for Crop and Disease Management; Curtin University; Bentley 6102 Perth Australia
3. ADAS UK Ltd, High Mowthorpe; Duggleby, Malton YO17 8BP UK
4. Agriculture and Horticulture Department; Fera Science Ltd; Sand Hutton York YO41 1LZ UK