Extending Mechanical Harvesting of 'Valencia' Sweet Orange into the Late Season Using Winter Drought Stress

摘要

Mechanical harvesting in late season ' Valencia' oranges can be problematic because mature fruit and next year' s young fruitlets are present during harvesting. Late in the harvest season, fruitlets can become large enough to be removed during mechanical harvesting thereby diminishing next year' s yield. We hypothesized that if the onset of spring bloom (about March) could be delayed using winter drought stress, the delayed younger fruitlets would be smaller and less susceptible to late season (after May) mechanical harvesting losses. During 2007 and 2008 seasons, 13-year old ' Valencia' orange trees were drought stressed by stopping irrigation and covering the soil beneath canopies with rain-out shelters for 100 days from Dec to Feb. The more numerous bloom occurred in trees that received rain only without irrigation. Drought stress from rain-out shelters was effective in delaying bloom 2-3 weeks without causing yield losses in the current crop in both 2007 and 2008. Drought stressed trees bloomed less but set a larger percentage of fruit such that there were no differences in the number of young green fruit by July for next year' s crop. During mechanical harvesting, there was less young fruitlet loss in previously drought stressed trees than in continuously well watered trees. Fruit growth after drought-delayed bloom caught up with irrigated treatments. Thus, winter time drought stress effectively delayed flowering and decreased young fruit loss during late season mechanical harvesting of ' Valencia' oranges.