Influence of spray application parameters on the deposit in an asparagus crop

A commercial air-assisted sprayer was tested in asparagus crop using a water-soluble food dye as a tracer. The machine had been modified by lowering the nozzles and the air outlets by 20 cm, in order to match more close by the geometry of the asparagus crop canopies and to improve deposition at the base of the stems. Several tests were performed to investigate how deposition was affected by various treatments, including: the number, position and size of the nozzles; the spray volume rate; the presence or absence of air assistance; the spray output angle, relative to the travel direction; and the forward speed. The most uniform deposition was obtained with: four nozzles per side (the lowest at a height of 46 cm from the ground), directed horizontally; an air flow rate of 6.1 m(3)/s; and a forward speed of 1.69 m/s. This adjustment was eventually compared with the standard sprayer setting, showing that total deposition on the canopy could be increased from 48.4 to 65.6% of the dose applied, without substantially increasing spray losses to the ground. (C) 1999 Silsoe Research Institute.