Cold Protection of Strawberries

Craig Chandler, UF/IFAS, Gulf Coast Research & Education Center

While strawberry crown tissue isn't usually injured until it reaches a temperature of about 20°F, damage to flowers and fruit can start to occur when tissue temperature reaches 30°F. Sprinkler irrigation is the standard method for protecting strawberry flowers and fruit from freeze damage. This method of protection is convenient and can be highly effective, although it can also damage fruit (water soaking and cracking), spread disease inoculum, and result in the loss of bed integrity. Most of the freeze events in Hillsborough and Manatee County (where the main strawberry production area is located) are radiation freezes (little or no wind), with air temperature typically bottoming out in the low 30s or high 20s. In this type of freeze, growers will generally wait to turn on their sprinkler irrigation system until the air temperature just above the plastic mulch, in an area open to the sky, is 31°F. Standard practice for a system where sprinklers are spaced 50 ft. x 50 ft. is to use 9/64-inch nozzles in the sprinkler heads and run the system so that there is 75 pounds of water pressure to the heads. Such a system should apply water uniformly and in sufficient quantity (about 0.15 inch per hour). It is important that sprinklers make at least one revolution per minute for adequate freeze protection. When an advective (windy) freeze is expected, and temperatures are predicted to drop into the low to mid 20s, it is common practice to use 11/64-inch nozzles (to provide the additional water needed for protection) and turn the sprinkler system on when the air temperature reaches 34°F. However, if wind speeds are 10 mph or greater, at least some flower and fruit damage is likely to occur. Once the sprinkler system has been turned on, it should remain on until the wet bulb temperature has risen above 32°F.

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