Quantifying pesticide deposits and spray patterns at micro-scales on apple (Malus domesticus) leaves with a view to arthropod exposure

1. TITLE Quantifying pesticide deposits and spray patterns at micro-scales on apple (Malus domesticus) leaves with a view to arthropod exposure 2. RUNNING TITLE Quantifying pesticide residues and spray patterns at micro-scales 3. AUTHORS Joanna T Witton Environment Department, University of York, Heslington, York, YO10 5NG, United Kingdom Corresponding author: joanna.witton@york.ac.uk ORCID 0000-0003-3751-4294 Matthew D Pickering Environment Department, University of York, Heslington, York, YO10 5NG, United Kingdom matthew.pickering@york.ac.uk ORCID 0000-0002-6234-2108 Tania Alvarez EcoRisk Solutions Ltd., The Kernel, Walnut Hill, Surlingham, Norwich, Norfolk, NR14 7DQ, United Kingdom tania.alvarez@ecorisksolutions.co.uk Melissa Reed Chemicals Regulation Division, Health and Safety Executive, Mallard House, 3 Peasholme Green, York, YO1 7PX, United Kingdom melissa.reed@hse.gov.uk Gabriel Weyman ADAMA Agricultural Solutions Ltd., 15 Thatcham Business Village, Colthrop Way, Thatcham, Berkshire, RG19 4LW, United Kingdom gabe.weyman@adama.com Mark E Hodson Environment Department, University of York, Heslington, York, YO10 5NG, United Kingdom mark.hodson@york.ac.uk ORCID 0000-0002-8166-1526 Roman Ashauer Environment Department, University of York, Heslington, York, YO10 5NG, United Kingdom roman.ashauer@york.ac.uk ORCID 0000-0002-9579-8793 4. ADDRESS WHERE WORK WAS UNDERTAKEN Environment Department, University of York, Wentworth Way, York, YO10 5NG, UK 5. ABSTRACT AND KEYWORDS BACKGROUND Pesticides used in commercial crop systems can adversely affect non-target arthropod populations. The spatial distribution of pesticide residues is rarely studied at scales relevant to these populations. Here we combine two methods for assessing pesticide spray deposits at spatial scales relevant to non-target arthropods found in apple orchards. Pesticide residues were determined on individual apple leaves through conventional residue analysis; water sensitive paper was used to investigate spatial distributions in deposits at the micro scale. We also evaluated how accurately a digital image analysis program estimated pesticide residues. RESULTS We found mean pesticide spray coverage on water sensitive paper varied by up to 6.1% (95% CIs [9.4%; 2.7%]) within an apple orchard, and leaf residues varied by up to 0.95 mg kg-1 (95% CIs 0.54 – 1.36 mg kg-1) within a tree. Leaf residues based on analytical chemistry were six times lower than pesticide deposition estimated through image analysis of water sensitive paper, though these correlated strongly. This correlation allowed estimation of actual residues by application of a correction factor. CONCLUSION Our method demonstrates accurate estimation of pesticide deposits at the individual leaf scale through digital analysis of water sensitive paper and is a low cost, rapid alternative to conventional residue analysis techniques.