Comparison of string and ribbon samplers in orchard spray applications

The main objective of this study was to establish the relationship between spray deposition on ribbon and string samplers in field applications. The experiment involved five commonly used citrus air-carrier sprayers, which included both conventional and tower configurations, equipped with axial- or cross-flow fans and hydraulic nozzles or rotary atomizers. A sampling structure, consisting of vertical and horizontal lines of polyester string and cotton ribbon, was constructed in a citrus grove. Spray mixtures, containing a fluorescent tracer, were applied at different volume rates and ground speeds (nine treatments) on a 30 m course between two tree rows. Shortly after spraying each replication, the lines were collected in pieces. In the laboratory, the amount of deposit was determined by fluorometry. Weather data recorded during the applications were used as co-variables in the analysis of variance. Each treatment was replicated 3 to 5 times. The results showed a significant difference between capture efficiencies of the two target types. In all sample locations, the amount of spray deposit on the string was higher than that captured on cotton ribbon. Overall, the mean and standard deviation of the string/ribbon deposit ratios were 2.3 and 0.7, respectively.