Abstract
Microsprinklers located either at the tree base, at 3 or 6 ft within the canopy, or at the tree top, were used for cold protection of 13-year old 'Hamlin' orange trees (Citrus sinensis (L.) Osb.) on sour orange rootstock (C. aurantium L.) during the windy freeze of 5 Feb. 1996. Minimum air temperatures reached 20-23ordm;F for the 0.8 acre study grove in Gainesville, Florida. The number of microsprinklers (1-3), application rate (15.0-31.5 gal per tree per hr), and spray pattern (90-360ordm;) were also varied. Three trees per treatment were evaluated on 6 March for percent defoliation in each of four canopy quadrants, and according to location (northwest, center, southeast) in the grove. The greatest defoliation was observed in trees which had three microsprinklers located at the tree base, trees which had two base sprinklers and one at 3 feet and also trees which had one cone sprinkler in the tree top. Leaf injury was greatest in the northwest quadrant of all trees. Injury decreased from the northeast to the southwest and southeast quadrants, regardless of treatment. The highest mean percent defoliation was observed in the northwest grove location whereas the lowest percent defoliation was in the center part of the grove. This preliminary experiment suggests that during moderate, windy freezes, leaf damage in mature trees may be affected more by tree location in the grove and position in the tree canopy than by the number or distribution of microsprinklers in the tree.
