Abstract
The effects of Prosulfuron, an experimental abscission chemical, on the loosening of 'Hamlin' and 'Valencia' oranges for mechanical harvesting were studied. Foliar applications of Prosulfuron were effective in loosening 'Hamlin' oranges, an early season cultivar, at 30 and 45 ppm. The optimum window for harvesting was 8 to 11 days after application. When applied during the bloom period, Prosulfuron caused complete abscission of exposed 'Hamlin' flowers. Pitting of the peel was observed at the 3 concentrations tested (15, 30, and 45 ppm). Although Prosulfuron loosened 'Valencia' fruit, a late season cultivar, the response was erratic depending on the time of application. Twenty-one days after treatment of Prosulfuron at 30 ppm the percent drop of mature fruit was 6.8%, 31.0%, and 11.0% when applied on April 7, April 30, and May 15, respectively. Starting 8 days after application, Prosulfuron induced excessive drop of immature fruit, which severely reduced the next year's crop. Prosulfuron was an effective agent for loosening the early season cultivar, 'Hamlin', for harvesting but was erratic and unpredictable for 'Valencia' the late season cultivar.
