CITRUS: SURVIVAL AT -11.1C TEMPERATURE DURING THE 1989 FREEZE
During the 1989 freeze, a scaffold branch irrigation freeze protection system was in operation on five-year old `Washington' navel and `Owari' satsuma trees and several younger trees of various navel orange varieties, a cold tolerant satsuma selection and other navel orange trees. Temperature dipped to a low of -11.1C, with 20 consecutive hours of -6.7C or below and 80 consecutive hours of 0C or lower. Post freeze evaluations and ratings show that an average tree survival rate of 94.6% was obtained. An average of 84.6% survival of scaffold branches and an average of 11% canopy survival was also achieved through the use of scaffold branch irrigation for freeze protection. Trunk injury ratings averaged 8.8 (scale 0-10; 0 – dead, 10 – no injury) and shoot regrowth after pruning dead wood averaged 8.0 (scale 0-10; 0 – no shoot regrowth, 10 – excellent shoot regrowth. The average percentage of the regrowth was slightly above 80% of the original tree volume prior to the freeze. Nonprotected trees sustained 100% kill and necessitated removal and reestablishment.