Hand thinning is not often applied as a commercial cultural practice in citriculture due to the practice’s reliance on costly manual labor. However, hand thinning could provide unique benefits such as treatment selectivity and easier control over thinning intensity, as opposed to foliar sprays of chemical thinning agents. In ‘‘on-year’’ ‘Nadorcott’ mandarin (Citrus reticulata) trees, summer (January) and autumn (April) hand-thinning treatments of removal of all fruit <20 and <40 mm diameter were evaluated for effects on leaf carbohydrates and fruit growth rate. Other factors assessed included treatments’ effects on tree total fruit yield, fruit quality, and fruit size distribution. In addition, two different summer hand-thinning treatments (removal of all fruit <20 and <25 mm) were evaluated for effects on fruit size distribution and fruit yield over two seasons to determine their potential financial implications.

Summer hand thinning reduced the numbers of small fruit and increased initial growth rate of prevailing fruit. This resulted in larger numbers of premium-sized fruit per tree, without treatments reducing total fruit yield and fruit quality. Additional labor was eliminated by quicker picking of fruit during harvest, and in season 2, fruit yield was higher for summer hand-thinning treatments compared with control. A higher potential income resulted from change in fruit size distribution and the breaking of alternate bearing over the 2-year period. The results provide producers of late mandarin cultivars with an alternative to chemical thinning agents to manage crop load and improve fruit size in individual ‘‘on-year’’ trees.

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Ockert P.J. Stander and Paul J.R. Cronjé