Abstract
Mechanical harvesting often causes visible injuries that can include shedding of leaves, flowers, and young fruit, breaking of branches, scuffing of bark, and exposure of root systems. To assess the impacts of mechanical harvesting on the health status of citrus trees, we measured removal of mature fruit, leaves, and shoots, mid-day drought stress and leaf photosynthesis of mature 'Hamlin' and 'Valencia' orange [Citrus sinensis (L.) Osb.] trees under restricted or normal irrigation regimes. Trees were either harvested by hand or with a linear-type trunk shaker operating at 4 Hz with 70.8 kg weight, and a 13 cm trunk displacement for various shaking durations. Shaking treatments removed 90% mature fruit without bark damage. Compared to harvesting by hand, trunk shaking removed 10% more leaf area and twigs, and occasionally caused some root exposure. Trees in dry soil developed drought stress symptoms after prolonged trunk shaking. However, no significant impairment of physiological responses by mechanical harvesting was found when trees were properly irrigated before and after harvest. Return bloom, growth, and yield of 'Hamlin' were not affected. Trunk shaking at full bloom did not affect 'Valencia' fruit set, but trunk shaking after mid-May can reduce next year's crop due to removal of immature green fruit.
