Ground Cover Supplement : GC Supplement - Spray application technology
GROUND COVER SPRAY APPLICATION TECHNOLOGY 12 Whole system set-up must be considered Boom height adjustment has been shown to be the most important variable that influences the risk of spray drift from ground rigs By Paul Miller SPRAY DRIFT IS a function of many factors including atmospheric conditions, spray liquid properties, sprayer set-up and operating speed. Research by Paul Miller and colleagues at Silsoe Spray Applications Unit in the UK has established that the value of using drift-reduction nozzles can be obliterated if the spray boom is set too high above the crop. While the doubling in speed of a cross wind doubles the risk of spray drift, increasing the height of the boom spray from 500 millimetres to 1000mm above the surface of the crop increases the risk of spray drift between five and 10- fold. For drift to be controlled, booms must be DRIFT-REDUCTION TECHNOLOGY Having the spray boom set too high increases the risk of drift and can negate the benefits of low-drift nozzles. For drift to be controlled, booms must be maintained at 500 millimetres above the top of the crop. maintained at 500mm above the top of the crop. The influence of boom height on the risk of drift has recently been confirmed in both wind tunnel and field studies in the UK. Wind tunnel studies have shown: nincreasing boom height by 200mm (from 500 to 700mm) can increase the risk of drift by up to a factor of four when using reference 110˚ '03' conventional flat-fan nozzle designs; nan increase in boom height of 200mm can mean that the drift from air-induction nozzles, selected to control drift, is then up to twice that of a conventional nozzle operating at the lower boom height; ndoubling the height of a boom from 500 to 1000mm increases the risk of drift between five and 10 times -- this compares with a doubling of the drift risk if wind speed is doubled; and nextended-range/variable-pressure nozzles give increased levels of drift -- although recent studies have shown that the detail design of these nozzles significantly influences the risk of drift. Similar results have been verified in field trials. It is concluded that control of boom height is the most important action relating to effective drift control with boom sprayers. □ More information: Dr Paul Miller, Silsoe Spray Applications Unit, email@example.com Water sensitive paper is a useful tool for checking spray quality and the deposition of spray in the paddock (see diagram p11).
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