Laboratory Device to Assess the Effect of Mechanical Thinning of Flower Buds, Flowers and Fruitlets Related to Fruitlet Developing Stage

Abstract

Mandarin thinning is done by hand, increasing labor costs and raising total cropproduction costs. Mechanical thinning has been tested in peaches and other fruits. To achieve themaximum efficiency thinning has to be applied at a specific stage of vegetative development. In thisresearch study, the mechanical thinning of ‘Clemenrubi’ mandarin branches during the differentfruit development stages have been assessed using a vibratory laboratory device (amplitudes 0.015and 0.030 m and frequencies 34.8 and 37.8 Hz). Branches with flower buds, flowers, small greenfruits, and medium green fruits were tested for 12 weeks, in two different seasons. It was possibleto mechanically detach flower buds, flowers, and green fruits using different combinations ofamplitudes and frequencies. Removal percentage decreased when increasing retention tractionforce, according to a logarithmic regression model. A significant increment in equatorial diameterand retention traction force was registered when the fruit setting was finishing, while mass had asimilar development with a week delay. During fruit setting (weeks 5, 6, and 7) removal percentagewas higher, while the retention force was very low. The first weeks just after the natural thinningcould be considered the adequate time for a mechanical thinning operation.