Application of the Abscission Agent 5-Chloro-3-methyl-4-nitro-1H-pyrazole Does Not Affect Peel Integrity or Postharvest Decay of Mechanically Harvested Late-season Fruit of ‘Valencia’ Orange during the Normal Commercial Harvest-to-processing Period

Abstract

In Florida, the combined use of mechanical harvesters and the abscission agent 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) for late-season harvesting (May to June) of fruit of ‘Valencia’ orange is effective at removing mature fruit with minimal adverse effects on the subsequent season's crop. However, CMNP can cause fruit peel scarring, and no data were available on how this affects peel integrity and potential losses resulting from fruit crushing and/or decay before processing. In this study, two late-season harvest dates were tested in commercial orchards during 2009 and 2010. Harvesting treatments consisted of combinations of two mechanical harvester ground speeds (0.8 and 1.6 km·h−1), two harvester shaker head frequencies (185 and 220 cycles/min), and CMNP foliar applications (4 days before harvesting) at 250 and 300 mg·L−1 in a spray volume of 2810 L·ha−1 plus mechanically-harvested and hand-picked controls. After harvesting, fruit samples were randomly collected from each block for peel resistance and postharvest decay evaluations. Peel resistance was determined by measuring both peel puncture force and fruit crush force. Fruit used to study postharvest decay were stored at 27 °C and 50% relative humidity or ambient conditions and evaluated daily for 8 days. Peel resistance was unaffected by mechanical harvesting combinations or CMNP application. No significant effects on postharvest decay were found among treatments for at least 3 days after harvest. However, a significant increase in postharvest decay between CMNP-treated and untreated fruit began between 4 and 6 days after harvest such that by 8 days after harvest, decay was as high as 25% in CMNP-treated fruit. The results indicate that CMNP can be safely used in combination with late-season mechanical harvesting under the conditions described in this study without losses resulting from fruit crushing or decay for at least 3 days, a time period well within the normal commercial harvest-to-processing time of ≈36 h.