Rootstocks Influence Cold-Hardiness of Georgia Tangos

Josh McGillCold Hardy, freeze, Rootstocks

Since the Christmas freeze of 2022, University of Georgia Lowndes County Extension Coordinator Jake Price has been conducting cold-hardiness ratings to see how Georgia citrus varieties were influenced by their rootstocks.

He focused on Tango performance in a recent report and declared US-1516 “the clear winner” in providing cold-hardiness.

Since January of 2023, Price has conducted ratings on how much foliage was retained after the freeze, which trees developed freeze cracks, diameter of limbs lost, and how much of the canopy was lost due to the freeze. He has been rating trees and removing limbs since March. Price is wrapping up those ratings as the 2023 harvest season is about to begin. 

According to Price, rootstocks did have an influence on cold hardiness. He ranked the rootstocks based on canopy loss from least to most (see table).


Price’s report includes the following findings:

Trees on US-1516 had the least canopy loss at 8%. US-812 and UFR-17 rated second and third for the least canopy lost. US-1516 also had the least number of trees with freeze cracks and had the highest percentage of foliage retained after the freeze. US-1516 also had the smallest diameter of limbs removed, and five of nine of the trees had no limbs lost greater than 10 millimeters, which is less than half an inch in diameter. 

On the other end of the spectrum, trees on US-852, Rich 16-6 and US-1279 had the most canopy removed. One would have expected Rich 16-6 to have performed better since it is a pure trifoliate. One reason that it may not have performed better was that seven of nine of these trees were replaced a year later with larger trees as these trees were smaller than the others when they were planted. However, the two oldest trees on Rich 16-6 that were growing well and not replaced had significant cold damage. 

The average canopy loss for all the trees was 30%. US-1516 was the clear winner in providing cold-hardiness in the Tango trial. US-812 and UFR-17 also performed well compared to the others. UFR-7 appears to have the most fruit of any of the rootstocks, but this will need to be verified after harvest. 

Most trees have very little fruit this year. Up until last year, there was little to no cold damage to the Tangos, and they have endured temperatures down to 20 degrees in their two previous winters. 

Source: Georgia Citrus Association

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