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There are approximately 27 million acres (4) of crop sprayed with herbicides each year in the prairie region of Western Canada. The use of phenoxy herbicides such as 2,4-D and MCPA for weed control, has resulted in significant increases in crop yields because the moisture norm ally used by the weeds is made available to the crop. The majority of the herbicides are applied by boom type ground sprayers although aircraft spraying is also employed. Boom type ground sprayers are equipped with nozzles which atomize the spray material in order to increase the surface area of the liquid, which results in more uniform and effective coverage. The nozzles produce a droplet spectrum consisting of a wide range of drop sizes. The smaller droplets (less than 100 microns in diameter) at the lower end of the droplet spectrum are a potential spray-drift hazard. Spray-drift may be defined as the movement of air-borne spray particles or droplets from the area of application to adjacent areas by wind or air cunents3. This is undesirable, particularly in areas where specialized crops that are susceptible to the herbicide are grown. Some plants that are particularly susceptible to small quantities of phenoxy herbicides are rape seed, sugar beet, sunflower, garden, flower, shelterbelt and shrubbery. The spray-drift problem is not a new one and much work has been done in this area. Some of the approaches that have
winnowing as a means of removing small drops from a spray pattern
Weins, E.H. and F.W. Bigsby 1971. WINNOWING AS A MEANS OF REMOVING SMALL DROPS FROM A SPRAY PATTERN. Canadian Agricultural Engineering 13(1):13-18.
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