MICROSPRINKLER IRRIGATION FOR FROST PROTECTION OF CITRUS IN FLORIDA

In 1979, it was not known if microsprinkler irrigation could provide any frost protection for citrus, and some assumed that this irrigation method would not. Tests during freezes between 1980 and 2010 showed that microsprinklers were effective in protecting the lower 0.9 m of young citrus trees, thereby saving the bud union and allowing later regrowth. Microsprinklers also benefit mature trees. The amount of air temperature warming depends on several factors, including volume of water applied, dew point temperature, and wind speed. Microsprinkler irrigation is more effective for cold protection when higher volumes of water are applied. Irrigation rates of 18.7 m³ ha^-1 h^-1 have been recommended. At these rates, average air temperature warming at a 1.2 m height is 0.6 to 1.4°C. At tree heights of more than 2.4 m, warming is commonly less than 0.5°C. In windy, low humidity freezes, evaporative cooling can damage trees, particularly if the emitter is on the downwind side of the tree. Protection is better if the microsprinkler is placed on the upwind (north or northwest in Florida) side of the tree. Microsprinklers elevated to a height of 0.6 to 0.9 m protect more of the tree than those at 0.2 m. While it was initially thought that microsprinklers provided no frost protection to the fruit, recent research has shown that this irrigation can promote better production of juice and kg of soluble solids than when no irrigation is used. Microsprinkler irrigation has become the most commonly used form of frost protection in Florida citrus.