The objective of this research was to determine the relationship between spray deposition and abscission efficacy of (CMN-Pyrazole), in mechanical harvesting of the ‘Hamlin’ orange. Two tests were conducted on 1/6/00 and 2/11/00 using an air-blast tower sprayer. The sprayer was equipped with an axial-flow fan and hydraulic nozzles. The trees were sprayed at three nozzle arrangements so that 3/4, 1/2, or 1/4 of the total discharge was directed to the upper half of the tree canopy and the rest to the lower half. Spray mixtures, containing CMN-Pyrazole (Release®), adjuvant Kinetic, and a fluorescent tracer, were applied at 2.6 km/h, 3,750 L/ha and 4.0 km/h, 2,450 L/ha, in the first and second tests, respectively. Leaf samples were collected from different canopy locations and spray deposition was quantified by fluorometry. Four to five days after the applications, fruit detachment force (FDF) was measured, dropped fruit was counted, the trees were shaken with a trunk shaker, and percentage of fruit removal was determined.
Mean canopy deposition was similar for all treatments. Deposition at different canopy heights was not proportional to the amount of spray directed to that height. The situation was improved in the second experiment, probably due to the lower application rate and reduced runoff. There was no difference in deposition between two sides of the canopy. Outside canopy deposition was higher than inner canopy deposition in most locations. In general, spray applications were effective in reducing FDF. There was stronger correlation between spray deposition and FDF in the second test. FDF was higher in the upper canopy compared to lower locations in the unsprayed control trees. Fruit removal efficiencies of sprayed trees were significantly higher than those of the unsprayed control in the second test.