Interaction of CMNP concentration and canopy shaker setting on fruit removal of sweet orange

Abstract

Maximizing fruit removal and minimizing tree injury are two goals for mechanical harvesting of sweet oranges for the citrus juice industry. CMNP (5-chloro-3-methyl-4-nitro-1H-pyrazole) is an abscission agent that is in the process of being labeled as an aid to mechanical harvesting. CMNP was applied to ‘Hamlin’ groves at 0, 200, and 300 mg·L–1 in a spray volume of 300 gal/acre in three trials that were conducted in mid December, early January, and late January. Dates for CMNP application were chosen when air temperatures would be near or above 15.6 °F and no rain forecast during the first 24 h after application. Four days after application, the trees were mechanically harvested with a pull-behind canopy shaker operating at frequencies of 3.0, 3.7, and 4.3 Hz and a tractor speed of 1.0 mph. The study was conducted as a randomized complete block, split plot design with canopy shaker frequency as the main plot and CMNP concentration as the split plot. There were four blocks and three trees per plot. Successful fruit loosening was demonstrated by preharvest fruit drop, which was higher for CMNP-treated trees compared with the no CMNP controls. Fruit drop was almost 35% for the 300 mg·L–1 treatment in late January but was below 7% for the controls in all trials. There was a signifi cant interaction in percent fruit removal by the canopy shaker between CMNP concentration and mechanical harvester frequency for all three dates. The difference among CMNP treatments was more evident at lower mechanical harvester settings. These results demonstrate the benefits of fruit removal by CMNP, especially at lower mechanical harvester settings.