A Model to Predict Loosening of Sweet Oranges by An Abscission Agent As An Aid to Mechanical Harvesting

About 7% of the sweet oranges are mechanically harvested in Florida, but with the recent submission for registration of the abscission agent 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP), the acreage is expected to expand.  CMNP is an effective promoter of abscission, although efficacy is affected by several factors the most important of which include coverage, concentration, air temperature, and precipitation.  Under optimal conditions, harvest should occur within 3 to 5 days after application for mechanical harvesters equipped with catch frames.  Air temperature during the harvest months often fall below the optimum that promote loosening.  A model that predicts the rate of loosening that incorporates predicted air temperatures would be useful for scheduling spray applications and harvest.  Scheduling spray applications and harvest must be conducted carefully to maximize fruit recovery, defined as the percent of the total yield on the catch frame after harvest, and thus must balance the extent of loosening and fruit drop.  A mathematical model is described that incorporates CMNP concentration, air temperature, month, and days after CMNP application to predict the extent of loosening.  Harvest should be conducted when fruit detachment force decreases by 50%.  The model was developed using data from several studies under a variety of field conditions and tested using data from other field studies.  Predictibility and limitations of the model are discussed.