DOWNWIND RESIDUES FROM SPRAYING A SEMIDWARF APPLE ORCHARD

Airborne spray and ground deposits were measured downwind from a row of semi-dwarf apple trees sprayed with an orchard air sprayer. Airborne spray collectors used were: string, plastic tape, bottles, and high-volume air-sampler filters; collector locations were at 7.5 to 240 m from the tree row, 0.5- to 10-m elevation. Ground deposits were collected on lines perpendicular to the tree row and at distances from 3 to 240 m downwind from the tree row. A mixture of water and a fluorescent tracer was sprayed on the trees at 468 L/ha during a total of 16 passes on four days and climatological data were recorded Ground deposits decreased from 1000 mug/m2 at 3 m to less than 30 mug/m2 at 30 m from the tree row; the largest deposits at 30 m were measured on day 4, when wind speeds were between 2.5 and 4 m/s. At the 30-m distance, deposits from spraying with and without trees were similar. At all locations, airborne spray deposits were greater than ground deposits. At locations less than 30 m, the greatest airborne spray deposits were measured when the trees were sprayed during bloom (less than full leaf). At locations greater than 30 m, the greatest deposits were measured on day 4, when the wind velocity was greatest.