Interaction of CMNP Application and Harvest Date of ‘Hamlin’ Sweet Orange

Robert C. Ebel, Kelly T. Morgan, Fritz M. Roka


This study was conducted to determine the change in mechanical harvest efficiency over time of sweet orange treated with the abscission agent 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP). CMNP was applied in December on ‘Hamlin’ at 0 and 300 mg·L–1 in a carrier volume of 2806 L·ha–1. The trees were harvested 2, 3, 4, and 6 d after CMNP application with a pull-behind canopy shaker operating at 3.7 Hz and with a tractor speed of 1.6 km·h–1. Fruit detachment force of CMNP-treated fruit declined to 39 N, which was 40% lower than the controls, by 4 d after CMNP application. The percent of fruit drop increased to 5% for CMNP treated fruit by 4 d compared to the controls that were significantly lower with 1% drop. The CMNP × harvest day interaction for the percentage of the crop removed by the harvester was not significantly different. The CMNP main effect mean was significant with CMNP removing 73% of the crop compared to 68% for the controls. The widest separation between CMNP treated and controls trees for the amount of fruit left in the trees after mechanical harvest occurred on day 4, where only 23% of the crop had to be gleaned for CMNP-treated trees compared to the controls that required 36% of the crop to be removed by hand. This study demonstrated that CMNP was active up to 4 d after CMNP application with the concentration and carrier volume of CMNP as used here and with air temperatures optimum for loosening (>15.6 °C) for most of the loosening period.


mechanical harvesting, abscission, harvest efficiency, 5-chloro-3-methyl-4-nitro-1H-pyrazole

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