Abstract
<b><sc>Abstract.</sc></b> Three separate studies were conducted in 2020-2021 to assess airblast spray drift in California almond (âIndependence‘ variety), citrus (mandarin), and table grape (âVintage Red‘ variety) based on a common protocol, similar to studies done in Washington apple. The overarching objective was to generate data for developing/validating a mechanistic model for estimating pesticide drift. Pyranine fluorescent dye (Sodium 8-hydroxypyrene-1,3,6-trisulfonate) solution spray was applied in 20-22 trials with the sprayer making four passes along the third drive lane upwind from the edge of orchard/vineyard. Airborne drift and drift deposition, expressed as percentage of applied rate, were quantified using flat plastic card, artificial foliage (AF), and horizontal polyester string (HS) samplers, which were analyzed by fluorometry. Meteorological data was recorded using two weather stations with sensors installed at different heights. Airborne spray drift (captured at downwind distances of 7.6 m and 22.9 m) and drift deposit were greatest in grape, followed by citrus, and then almond but sampling height was significant only in grape. However, data generated with the AF and HS samplers indicated the increasing order of downwind distance where drift deposit completely decayed to be, grape < citrus < almond. Analysis of the composite influence of crop characteristics and weather parameters revealed that canopy diameter, wind direction, wind speed, air temperature, and relative humidity were significant nearer the orchard/vineyard but dwindled in significance to different extents farther downwind. Inversely, solar radiation and atmospheric pressure were initially insignificant until further downwind. However, leaf area density was insignificant at all downwind distances. The results provide the opportunity to objectively assess downwind pesticide exposure from drift and a basis for improving methods to mitigate drift.
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