The potential losses from spray applications of glyphosate [N-(phosphonomethyl)glycine] with and without the inclusion of a polymer thickening agent were evaluated in field tests, applied under identified weather conditions with a boom-nozzle ground sprayer, helicopter, and fixed-wing aircraft. The downwind transport and diffusion of the spray loss was assessed by means of Mylar fallout sheets, high volume air samplers, and 4-leaf wheat(Triticum aestivumL. ‘Anza’) plants. Lowest drift losses occurred, under 0.01 g/ha on fallout sheets at 100 m, with deflector fan nozzles (KGF) operating at a low pressure (7 kPa) on the ground sprayer. Drift losses from a helicopter equipped with micro-jet nozzles were only slightly higher, less than 0.03 g/ha on fallout sheets at 100 m. Drift losses from 8003 nozzles mounted on a ground sprayer and D-6 jet nozzles directed back on fixed wing aircraft produced much higher drift deposits, from 0.2 to 1.0 g/ha on fallout sheets at 100 m. The highest levels of drift losses were obtained with D-4 jet nozzles directed down on a helicopter, 5 g/ha on fallout sheets at 100 m. Some evidence of reduced airborne drift was apparent where the polymer thickening agent was used with aircraft and ground equipment. The test results indicate that significant reduction in drift losses were obtained with proper application equipment; however, the use of a polymer thickening agent reduced drift only slightly for certain applications.
Hourly wind recordings at Davis and Grimes, California, revealed that spraying operations by aircraft in summer can frequently be extended beyond the customary sunrise hours without damage by drift to adjacent crops susceptible to the spray material. The data permitted scheduling spraying according to wind types. These wind records also revealed noteworthy meteorological peculiarities. The influx of the marine air beginning in the afternoon lasts almost all night, only being replaced by the opposite flow after sunrise. This indicates that the often heard “land and sea breeze” term is not appropriate, and that rather a monsoon flow tendency prevails. It is suspected that the daily variation is primarily influenced by a daily cycle in strength and northward extension of the Arizona Low.
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