Multi-county citrus Extension agent Chris Oswalt discussed historical and current freeze protection measures in a virtual Dec. 22 OJ Break.
Some cold-protection measures are taken well in advance of freezes; Oswalt referred to them as passive measures. They include grove site selection, crop selection and cultural practices.
One site selection consideration is planting groves at higher elevations, which are historically warmer than lower elevations.
Regarding crop selection, a grower might choose to plant early-season Hamlin oranges in hopes they’ll be harvested before freezes hit. Some rootstocks are also more cold-hardy than others.
Cultural practices that can offer freeze protection include mowing row middles to allow heat absorption into the soil during daylight hours, and proper nutrition and irrigation to reduce tree stress.
Among active cold-protection measures, the most common in Florida is the use of micro-sprinkler irrigation, which works in advection and radiation freezes, Oswalt said. Other active measures include wind machines in radiation freezes, and plant covers, which work best in radiation freezes. Oswalt noted that grove heaters, which were used several decades ago to keep groves warm on cold nights, are no longer used because the cost of fuel is too high to be justified economically.
Oswalt went into some detail about the use of irrigation for cold protection, discussing the importance of wet bulb temperature, dew point and other factors. “You can be, in certain circumstances, colder by using micro-sprinklers,” he cautioned.
He also told growers how to interpret weather forecasts to determine what types of freezes might be coming in the near future.
Oswalt and University of Florida Institute of Food and Agricultural Sciences researcher Davie Kadyampakeni recently wrote an article for Citrus Industry magazine detailing when and how to protect citrus trees from freeze damage. See their article here.
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