Efficacy of a solid set canopy delivery system (SSCDS) in sweet cherry and apple

To reduce reliance on airblast sprayers in sweet cherry (Prunus avium L.) and apple orchards (Malus domestica Borkh.), a solid set canopy delivery system (SSCDS) using multiple levels of sprinkler nozzles for trellised canopies is being developed. This study reports preliminary comparisons of application efficacy using common plant growth regulators (PGR). The bloom thinner ammoniumthiosulfate (2%) was applied through the SSCDS and airblast sprayer at ca. 40 and 80% full bloom. Efficacy was evaluated by assessing fruit set compared to an untreated control (UTC). In a separate experiment, gibberellic acid GA₃ (20 ppm) was applied to sweet cherry at late Stage II of fruit development. At harvest, treatment effects were quantified by assessing fruit quality. Lastly, we evaluated the efficacy of the SSCDS for evaporative cooling (EC) in apples, documenting its effect on fruit surface temperatures (FST) compared to a standard EC system. When ambient air exceeded 32°C, apple FST was measured using an infrared thermometer at regular intervals during and between cooling cycles. There was no difference in efficacy of application technologies in chemical thinning. Application method in the GA₃ trial did influence fruit quality. Airblast treated fruit exhibited decreased exocarp color (-14%) and increased firmness (+10%) compared to UTC. Fruit treated by SSCDS were heavier (+5%) than UTC. The SSCDS maintained apple FST below 27°C compared to 35°C from standard EC. The SSCDS may be a viable PGR application method and EC in trellised orchards; however continued engineering of nozzle type and placement is warranted.