Influence of Mechanical Harvesting on Citrus Quality: Cannery vs. Fresh Fruit Crops

Abstract

Abstract Mechanical harvesting has, of course, long been standard for many annual crops, the “combine harvester” for wheat being an early, and successful, example. In some instances (e.g., tomato, plant breeders have “tailor made” cultivars to adapt them to mechanical harvesting. Typically, such annuals are destroyed in harvesting. The plant must be preserved with perennial crops, although sometimes considerable injury to the plant can be acceptable when (as for grapes or raspberries) the plant is severely pruned annually. Substantial damage to the plant (tree) is not acceptable, in mechanical harvesting of tree crops, but leaf damage is of minor consequence for deciduous tree crops, and the fruit is biologically destined to abscise; if it is not harvested. Damage to the product is not a problem, it will soon fall naturally for some deciduous tree crops (particularly nuts of various kinds). In contrast, mechanical harvesting of citrus fruits involves quite extraordinary problems. The tree is evergreen and substantial leaf damage is not acceptable. The fruit has no clearly defined abscission period. The same grapefruit that might be picked in October can hang on the tree until May. Citrus fruits are extremely subject to decay. ‘Valencia’ (an important cannery orange cultivar) takes 12 to 18 months from bloom to acceptable maturity to complicate matters further. Thus, there are 2 crops on the tree at harvest time; mature fruit that are to be harvested and immature fruit that must not be damaged or removed. It is apparent after 20 years and millions of dollars spent in Florida that the problem (particularly for ‘Valencia’) is as much biological as it is mechanical. The fruit, but not the leaves, must be made to abscise and, for ‘Valencia’, the tree must retain the immature crop while releasing the mature fruit.