Volume 2, Issue 4 (April 2005)
Comparison of Abscission Spray Application Practices for Mechanical Harvesting of Oranges
Two air-carrier sprayers were used to investigate the feasibility of applying abscission materials from one side of the tree in a two-row bedded orange grove. One-sided (bed side) and two-sided (both bed and ditch side) applications at 2.4 and 4.8 km/h were compared using each sprayer. Tank mixture contained active ingredient (a.i.) 5-chloro-3-methyl-4-nitro-1-H-pyrazole (CMN-P) at about 350 mg/L a.i., a surfactant, a drift retardant, and a fluorescent tracer. Leaf samples were collected from different locations on the bed and ditch sides, and deposition was determined by fluorometry. The efficacy of abscission application was assessed in terms of fruit detachment force (FDF) and percent fruit removal (PFR) by trunk shakers.
With both sprayers, one-sided applications resulted in comparable depositions to two-sided applications at the far side of the lower canopy level. This result implies that one-sided applications might provide acceptable spray coverage in lightly foliated canopies. Abscission sprays at one-half or full a.i. (526 or 1052 g/ha) rate reduced fruit detachment force significantly. The best results were obtained with two-sided applications at lower ground speed (highest volume/a.i. rate). The air-curtain sprayer at full a.i. rate and the air-blast sprayer at one-half or full a.i. rate resulted in a significant increase in percent fruit removal.