Fruit Loosening Agents

Trunk-shaking mechanical harvesters have been evaluated for decades but to-date have been unable to harvest table olive fruit efficiently and without damage. Canopy shaking mechanical harvesters are currently under development and show promise. However, a fruit-specific abscission agent would facilitate fruit removal by lowering the mechanical force required to harvest the fruit, thus minimizing fruit damage. Fruit damage is an industry concern because bruising may compromise quality of the final canned product, although this remains to be tested. An acceptable abscission agent would selectively and predictably loosen olive fruit, and minimize leaf loss with no phytotoxicity and no impact on quality of the final product.

The use of agents to loosen fruit in olive has been under investigation for over 40 years. Compounds that release ethylene, such as ethephon, are effective at loosening fruit but also cause unacceptable tree defoliation with subsequent lack of bloom in the following year when used at concentrations high enough for immature fruit removal. Research in fruit-loosening compounds for table olives was stalled until recent work in Spain with oil olives found that foliar sprays with a proprietary mix of monopotassium phosphate with ethephon 15 days before harvest reduced the fruit retention force in olive with minimal leaf drop.

University of California, California State University, University of California Cooperative Extension and University of Florida researchers are collaborating to evaluate fruit loosening compounds, mechanical harvesters and methods to reduce fruit damage for the table olive industry. Their goals include investigating the potential of ethylene-releasing compounds as olive loosening agents, screening additional candidates previously shown to accelerate citrus fruit abscission, improving harvester efficiency and reducing fruit damage caused by mechanical harvest, and reducing fruit damage through the use of anti-oxidants.

Over the past season, we researched ethylene-releasing compounds and some showed some promise in reducing the pull force required to separate fruit from the trees. Preliminary results indicated that ethephon in combination with monopotassium phosphate, and a biosynthetic precursor of ethylene called ACC can significantly lower fruit removal force with reduced defoliation. Lowering fruit removal force will allow machines to harvest at a lower force, achieve high removal efficiency, and reduce olive bruising. We have also worked with a number of anti-oxidants and had some success with reducing the effects of bruising with post-harvest drenches. Our future work will focus on maximizing the potential of abscission agents for olive mechanical harvesting and further screening of additional candidates for abscission and maintenance of fruit quality.

Mechanical Harvesters | Overview