A survey by 15 Extension agents showed Sugar Belle mandarin to be the most cold-hardy non-satsuma citrus variety following a major freeze in Georgia in December 2022. Sugar Belle was followed in order of cold hardiness by Tango, navel oranges, Kishu and grapefruit. Shiranui was the least cold hardy non-satsuma variety.
University of Georgia Extension agent Jake Price reported the survey results.
Observations of satsumas a few months after the freeze clearly showed they were the cold hardiest variety, so the focus was on non-satsuma varieties. The agents participating in the survey rated non-satsumas planted in 2020 and before. Newly planted trees are much more susceptible to freezes, so trees that have survived at least two winters were chosen for the survey since they would be well established.
TREE RATINGS
Agents estimated the percentage of canopy loss in each tree. They then gave an overall visual assessment of each tree from 0 to 5 with 0 being dead and five having no visible freeze damage. Ratings from all the agents were combined and averaged to get the results.
The Sugar Belle mandarin had the lowest percentage of canopy loss (22%) and the highest visual assessment (3.3), indicating this variety tolerated the freezes the best.
Tango mandarin and navels were similar to each other in canopy loss and visual assessment and were behind Sugar Belle in cold tolerance. Tango had 35% canopy loss and a 2.4 visual assessment. Navels had 36% canopy loss and a 2.7 visual assessment.
Kishu mandarin and grapefruit had very similar canopy loss and visual assessment. Kishu had 51% canopy loss and a 2.1 visual assessment. Grapefruit had 55% canopy loss and a 2.1 assessment.
Shiranui had the highest percentage of canopy loss (60%) and the lowest visual assessment (1.7), making it the least cold hardy of these six varieties.
Other varieties were assessed but not included because there were so few ratings taken. These included Hamlin, lemons, UF-950, blood oranges, Bingo, Gold Nugget and UGA Sweet Frost.
The survey results represent ratings from 15 counties and sites in southeastern Georgia, southwestern Georgia and northern Florida. They may be helpful when choosing varieties to diversify the citrus industry. However, with so many variables and different locations rated, it is difficult to draw firm conclusions on cold hardiness. More work needs to be done.
FREEZE CRACKS AND FRUIT LOADS
In the survey, the percentage of trees with freeze cracks did not corelate with canopy loss. Many dead trees or severely damaged trees were observed with no freeze cracks, indicating trees likely died before forming freeze cracks.
Trees with heavy fruit loads seemed to suffer more freeze damage than trees with average or light fruit loads, so removing fruit as soon as possible will increase cold hardiness.
Trees that were less cold hardy in this survey may still be profitable as they have survived prior winters and have been producing fruit.
Source: University of Florida Institute of Food and Agricultural Sciences
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