EVALUATION OF SPRAY QUALITY BY OILAND WATER-SENSITIVE PAPERS

Nine spray treatments were applied to plots of orange trees, in a randomized complete block design and fourreplications. The treatments involved three air-carrier sprayers, operating at different volume rates and ground speeds.Spray mixtures contained a petroleum oil (Sunspray 7E) at a constant rate of 37.5 L/ha and water rates of 220 to3750 L/ha. Oil- and water-sensitive papers (OSP and WSP) were used as spray targets. The targets were placed at twoheights, outside and 0.3-0.4 m inside the canopy. At each location, both OSP and WSP were stapled to the upper andlower leaf surfaces of two neighboring leaves. Additional target pairs were also positioned rigidly on target holders, inthe gap between two adjacent trees, at two heights and at horizontal top, horizontal bottom, and vertical positions.Sprayed targets were analyzed by an imaging system. The percent area coverage, mean spot diameter, volume meandiameter, and spot density were used to evaluate distribution patterns. There was a substantial variation in distributionpatterns of different replicates. Both WSP and OSP patterns were significantly affected by the sprayer treatment andtarget location. The results were quite variable and the papers may have a limited value for quantitative assessment ofspray coverage or droplet size measurement of high spray application rates. Among all parameters, the percent areacoverage appeared to be the most reliable.