Field evaluation of air-assisted boom spraying on broccoli and potato

Field trials were performed in 1994 and 1995 on potatoes and broccoli in order to compare two different spraying techniques: air-assisted spraying and conventional spraying. In the field, a boom sprayer providing both air-assisted and conventional spraying was used. Air assistance was provided by creating a high velocity air curtain that spans the whole length of the boom. Nozzles were placed close and in front of the air exit and tilted such that the spray patterns from individual nozzles merged before droplets were fully entrained into the air curtain. A mix of water and fluorescent tracer was applied at application rates of 100 L/ha and 200 L/ha. Sampling was made at different heights within the plant foliage and on both sides of the leaves. The analysis was performed using image analysis to measure the area covered by droplets. Field results show that air-assisted spraying provides a better overall spray penetration and coverage than conventional application. The applications at lower volume (100 L/ha) using air assistance and the applications at higher volume (200 L/ha) without air assistance yield comparable results. Results from field experiments compare well to results from spray chamber experiments for broccoli but not for potato. A plausible explanation for this difference is that greenhouse grown potato plants were quite different than field grown ones while greenhouse and field grown broccoli plants were very similar.