Results of Providing Weekly Data on Citrus Tree Cold Acclimation to Florida Growers

The Polk County UF/IFAS Cooperative Extension Service provides citrus growers with citrus tree cold acclimation information during the winter. This information is used by growers to make informed decisions on the use of microsprinkler irrigation for citrus tree cold protection. Information on cold acclimation is generated in the lab using a process that measures electrolyte leakage from damaged frozen leaves. Leaf leakage is measured at progressively colder test temperatures to determine the critical temperature at which 50% of leaf cells are damaged. Field observations have held out the validity of using this 50% benchmark methodology as a threshold for citrus leaf damage. Beginning in 2005 eight central Florida grove locations per year have been used for the collection of weekly leaf samples from November 15 to March 15 of each year. Five leaves from the same six trees each year at each location are collected to determine the weekly citrus leaf freezing point temperatures. Data collected demonstrate the dynamic nature of citrus tree acclimation during the winter and between individual years. Critical citrus leaf freezing temperatures ranged from –8.30 °C to –2.7 °C depending on the year. Results of annual grower surveys indicate that there has been over the past seven years a significant percent reduction in the amount of irrigation water that has been pumped for citrus tree cold protection in central Florida. Grower’s average estimated savings over the seven year period ranged from no savings to over 50% depending on the year. The mean average water savings for the seven year period was 19.28% when growers considered the critical citrus leaf freezing temperature data in making cold protection decisions. This demonstrates that savings in water and pumping costs can be realized by the use of relevant research information that has been appropriately transferred to growers. However, recent field observations indicate that HLB (huanglongbing or citrus greening disease) has a significant negative effect on citrus tree cold acclimation. In the future, this apparent difference will need to be quantified in future citrus leaf freezing temperature determinations as the incidence of HLB increases in Florida.