Cold Acclimation and Leaf Freezing Temperatures

Tacy CalliesWeather


Citrus Extension agent Chris Oswalt reports the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is determining the acclimation of Florida citrus trees to cold weather by measuring citrus leaf freezing temperatures.

“Certain environmental conditions will initiate this acclimation process,” says Oswalt. “These environmental cues will cause physiological changes to occur within the plant that will depress the temperature at which plant damage will occur. Major environmental factors in Florida citrus are air temperature and water.”

According to Oswalt, at 55° F, citrus plant growth slows; as temperatures remain below 55° F, citrus trees will continue to acquire acclimation (plant cold hardiness) to these cooler temperatures. “This process is reversible during warm winter periods, and a loss of acclimation can occur,” he says. “This loss of acclimation (de-acclimation) can happen rather quickly under field conditions compared to the process of acclimation. The greatest amount of citrus acclimation occurs during a consistently cool fall and winter. Once de-acclimation occurs, citrus trees will generally not re-acclimate to the same level before the onset of de-acclimation.

“Irrigation and fall/winter rainfall can have a pronounced effect on citrus acclimation. However, visibly drought-stressed trees are more susceptible to freeze damage and HLB-induced fruit drop. The key here would be to provide adequate water to the tree with irrigation and manage that irrigation to not cause growth during the winter.”

Oswalt says cold hardiness in citrus is highly dependent on the vigor of the rootstock/scion combination, crop load, the susceptibility of plant tissue, tree water status, nutrition and other cultural practices that affect tree vigor.

This year, results of UF/IFAS citrus leaf freezing determinations can be found on the Florida Automated Weather Network here. New rootstock and variety combinations have been tested to provide better insight to growers in the acclimation process for these combinations. “We have been running determinations on Hamlin on Swingle and Valencia on US-942, along with Sugar Belle and Bingo on US-942,” notes Oswalt.

Source: Citrus from the Ridge to the Valley, January 2021

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