Abstract
The abscission agent 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) was applied at 200 and 300 ppm to ‘Hamlin’ trees in three trials from December through the end of January and to ‘Valencia’ in three trials from March through April to determine the spatial and temporal variation in fruit detachment force (FDF) and fruit drop up to 5 d after application. Average FDF varied from 18 to 97 N for ‘Hamlin’ and 42 to 119 N for ‘Valencia’ before CMNP was applied. A univariate analysis was used to determine the upper and lower 99% confidence limits and means for every sampling date. Linear regressions fitted to the three regressions for each cultivar and CMNP concentration were statistically significant at the P < 0.05 or P < 0.01 level. The slopes and CMNP concentrations were subjected to ANOVA, and the lack of an interaction indicated that the rate of loosening was similar regardless of initial FDF. The slopes for the lower and upper confidence limits and mean were similar for ‘Valencia’, but the slope of the lower confidence limit was lower than for the upper confidence limit and mean for ‘Hamlin’, indicating that ‘Hamlin’ fruit with low initial FDF loosen slower than fruit with higher initial FDF. An exponential function was found to fit well to fruit drop over time with regression coefficients ranging from 0.75 to 0.99. We propose that the relationships developed here would be useful in developing a predictive tool for mechanical harvesters with catch frames that minimizes the sum of fruit drop and fruit left in the tree after harvest.
