Pesticide Tracers for Measuring Orchard Spray Drift

Abstract

Airborne spray and ground level deposits of permethrin were measured downwind from semi-dwarf apple trees sprayed with an orchard air sprayer. Collectors were located from ground level to an elevation of 10 m (32.8 ft) and out to 240 m (787 ft) downwind from the sprayed tree row. A mixture of permethrin and water was sprayed at 468 L/ha (50 gal/acre) during nine passes on days 1, 2, and 3. The wind was light and variable on day 1 but wind speed was about 4 to 6 m/s (6.4 to 9.7 mile/h) on days 2 and 3. Ground level deposits decreased as downwind distance increased. On day 1, no permethrin was detected beyond 60 m (197 ft) from the tree row. At 30 m (98 ft) from the tree row, deposits on Line 1 (sprayed without trees) was about the same as deposits on Lines 2 and 3 (sprayed through trees). Airborne spray permethrin deposits were affected by wind speed; at all sample sites, deposits on strings at elevations from 1.5 to 4.5 m (4.9 to 14.8 ft) were less when wind speed was less. At the 60 m (197 ft) location, deposits tended to be more uniform over elevation than at locations closer to the sprayed trees. In general, deposits on string decreased with increased elevation.