Drift from orchard spraying

Abstract

Research from 1989 to 1996 into drift from air blast orchard spraying, principally in kiwifruit blocks with live shelter, is reviewed. A mass balance study showed 96% of applied vinclozolin could be accounted for with 75% on the target crop, 19% on the ground or shelter and about 2% leaving the block as drift. Summarising results from 21 trials gave trends for both deposited and aerial drift outside the shelter to decrease exponentially with distance (distance for 50% decline, d0.5, ca. 26 m). Chlorpyrifos, pirimiphos-methyl and particularly diazinon gave elevated drift levels that persisted after spraying ceased. This was attributed to volatilisation from the crop. Typical drift levels for a range of pesticides were 0.5-5mg/m3 in air samples and 20-200 mg/m2 in deposits 50 m downwind of shelter. Air measurements in urban areas 0.5-1 km from orchards detected low levels of chlorpyrifos and diazinon (5-40 ng/m3). Drift levels were not strongly influenced by formulation, water rate (500- 2150 litres/ha) or wind speed (0.5-5 m/sec). Risks to human health from drift outside sprayed blocks were assessed as minimal.