Comparative performance of recycling tunnel and conventional sprayers using standard and drift-mitigating nozzles in dwarf apple orchards

Abstract The use of tunnel sprayers should be encouraged because they can potentially reduce pesticide input and drift in orchards. They could also allow smaller plot size in multifactorial trials in which fully randomized or randomized block designs are recommended. However, the effectiveness of plant protection products applied with tunnel sprayers cannot be reliably assessed without a thorough investigation into spray distribution in tree canopies. A set of three experiments was undertaken in an apple orchard to compare a new type of recycling tunnel sprayer with a standard axial fan sprayer, both of them fitted with either conventional hydraulic hollow cone nozzles (ATR) or drift-mitigating air induction cone nozzles (TVI). Its performance was assessed in terms of 1) spray deposit and coverage in the canopy, 2) sedimentation drift (spray drift to the ground) and 3) collection and recycling rate of the liquid sprayed in the tunnel. Artificial targets composed of cellulose papers and water-sensitive papers were used to evaluate the spray deposit and coverage at similar target positions for each treatment. A fluorescent dye was used as the spray tracer. The study showed that, when using the ATR nozzles, the spray deposit, at each sampling point in the tree canopy, produced by the tunnel sprayer was not significantly different from that produced by the standard sprayer. The spray deposited on the top of the trees when using the TVI nozzles, however, was significantly less than with the standard sprayer. At the same spray deposit level, the spray cover on the canopy, estimated by image analysis, was relatively better with the standard sprayer than with the tunnel sprayer. At the same spray deposit level, the TVI nozzles resulted in significantly poorer spray cover of the canopy than the ATR nozzles. At low wind speeds, the sedimentation drift varied on average from 5.8 to 9.1% of the total sprayer output, irrespective of the type of sprayer or nozzle. The overall mean of the sedimentation drift was not significantly different for the two types of sprayers. The recovery system, which included a continuous recycling process in the tunnel sprayer, led to average savings of 28 and 32% of the applied spray mixtures for the ATR and TVI nozzles, respectively. The tunnel sprayer might therefore be suitable for small-scale apple orchards when fitted with traditional ATR nozzles rather than with air-induced TVI nozzles.