Reduction of spray pressure leads to less emission and better deposition of spray liquid at high-volume spraying in greenhouse tomato

In an experimental greenhouse, growing a tomato crop, it was investigated if a reduction in spray pressure could improve the spray result, while, simultaneously, emission to the ground could be reduced. Spray deposition on the leaves and the emission to the ground was evaluated at different spray pressures (2.5, 5, 10 and 15 bar). An Empas vertical spray mast with 6x2 Teejet XR8002VK flat fan nozzles was used to spray the tomato crop in three stages of crop growth, respectively 0.75, 2.25 and 2.80 m height, spraying 500-1500 l ha-1 (stage 1) and 1000-3000 l ha-1 (stage 2 and 3) depending on the spray pressure. Flow rate ranged from 0.74 to 1.80 l min-1 at an increasing spray pressure from 2.5 to 15 bar. The VMD (Volume Median Diameter) decreased in the same pressure range from 207 to 124 µm. The emission of spray liquid to the ground was measured in the spraying path and beneath the plants between the rows closest to the spray mast. The highest emission to the ground appeared closest to the spray mast, and increased at higher spray pressures. In crop growth stage 1 and 2 about 35% of the spray volume emitted to the ground, in stage 3 only 15%. The direction of the nozzles (upwards directed with an angle of at least 400) appeared to be of great importance. The deposition of spray liquid on the leaves was measured at two rows (A: closest to the sprayer, B: the next row behind it) at one, two or three heights depending the stage of the crop. Highest spray deposition could be found in row A, at the upper side of the leaf and at a higher working pressure. Differences were smaller in the next row and at greater height in the plant. Finally it could be concluded that a decrease in spray pressure to 5 bar gave an adequate deposition on the leaves in µl cm-2, and a decrease in emission to the ground.