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- Author or Editor: Jackie Burns x
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Mechanical harvesting using trunk shakers on late-season `Valencia' sweet orange [Citrus sinensis (L.) Osb.] trees can remove young fruit for the next crop and occasionally cause root exposure or severe bark scuffing on the trunk. To evaluate the effects of these physical injuries on fine root growth and lifespan, we installed minirhizotrons in the root zone of 15-year-old fruiting `Valencia' trees on Swingle citrumelo [C. paradise Macf. × Poncirus trifoliate (L.) Raf.] rootstocks. Images of roots against the minirhizotron tubes were captured biweekly with a custom-made video-DVD recorder system. Trees were harvested in early June by hand or with a linear-type trunk shaker in two consecutive years. Bark injury after trunk shaking was mimicked by removing part (42%) of the bark tissue from the main trunk with a sharp knife. Numbers of fine roots, root activity and lifespan as indexed by the color of the root, and the distribution of new fine roots after harvest were analyzed. Although root exposure was common with the normal operations during mechanical harvesting, few disturbances reached the major fine root zone. There was no clear correlation between root growth and trunk shaking with or without bark injury. The root system might benefit from less competition after the loss of young fruit from mechanical harvesting, as a greater availability of carbohydrates or other resources may compensate for any potential damage due to mechanical harvesting.
Continuous canopy shakers (CCS) were developed in the late 90's and have been used to commercially harvest citrus in Florida. A viable mechanical harvester in Florida must be able to selectively remove mature `Valencia' fruit. A study was conducted to evaluate the effect of operating conditions on mature and immature fruit removal during the 2003 harvest season. The study was conducted in the southern flat woods and northern ridge areas. The study treatments were completely random and replicated four times. The CCS treatments were 145, 215, 230, and 245 cycles per minute (cpm) and a hand picked control. The harvest occurred on 17 and 19 June at the southern and northern sites, respectively. Mature fruit removal linearly increased from 95.7% to 97.9% between 145 and 245 cpm, respectively. Varying the operating ranges significantly influenced mature fruit removal in the southern flat woods site. The trees at the southern site were taller (>4m), and had a larger crop load. At the northern ridge site where trees were smaller, varying the CCS operating ranges did not significantly influence mature fruit removal. Immature fruit removal was influenced by the operating ranges. Immature fruit removal was increased at least 22% over hand picked controls. The results were interpreted to indicate the frequency of CCS is dependent on tree size. The initial selectivity of the CCS was not equal to hand picking.
To determine the effects of abscission compounds 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) and ethephon on citrus leaf function and water relations, we applied CMNP at 0, 200, 500, 1000, or 2000 ppm, or ethephon at 400 or 800 ppm, to canopies of fruiting potted and field citrus trees during the harvest season. Both compounds induced fruit and leaf drop after 3 days of application, especially at high concentrations. Low concentrations of CMNP (0, 200, or 500 ppm) or either ethephon treatments did not affect leaf photosystem II efficiency, as indicated by leaf chlorophyll fluorescence (Fv/Fm). High concentrations of CMNP (1000 or 2000 ppm) immediately reduced photosystem II efficiency in leaves and fruit peel. However, Fv/Fm of leaves remaining on the trees was gradually restored and close to the level of control after 4 days of treatment. Both compounds had little effect on chlorophyll content, ratio of chlorophyll a to chlorophyll b, leaf water content, and mid-day leaf water potential. The results suggest that CMNP at recommended concentrations (200 to 500 ppm) effectively reduced fruit attachment force with little herbicidal effect on leaves.