Abstract
Two studies, one on ‘Hamlin’ and the other on ‘Valencia’ trees, were conducted to determine if short-term drought stress affects efficacy of 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMNP) for loosening fruit as an aid for mechanical harvesting. ‘Hamlin’ orange trees were drought stressed in late February by withholding irrigation for 5 days (control), 12 or 19 days before harvest and ‘Valencia’ orange trees were drought stressed in late April by withholding irrigation 0 (control), 4 or 7 days before harvest. Soil moisture, leaf conductance, transpiration and stem water potential were lower for the drought treatments compared to the controls. There was no significant interaction between drought stress and CMNP on fruit detachment force (FDF) or fruit drop. CMNP substantially decreased FDF and fruit drop; however, drought stress did not. These results indicate that drought stress from 7 to 19 days does not alter efficacy of CMNP.
