Freezing Temperatures:Almond Frost Sensitivity

There is a frost risk for the next few nights with temperatures dropping into the high 20's and maybe lower. If these forecasts are true, crop loss could be experienced within colder areas of almond orchards.As written previously, there are some tasks that can be performed to help reduce the risk of frost damage. These include mowing the cover crop or residual vegetation to allow radiant heat form the soil to move into the canopy, use of sprinkler systems to apply water which warms the orchard, or utilization of equipment or fans to help move warmer air into the orchard. All of this is to help increase orchard temperatures by 2-3 degrees.The risk of frost increases as almonds break dormancy and begin development. Dormant buds are relatively tolerant to freezing conditions, but sensitivity increases as flowers develop from pink bud to full bloom, then into nutlets. The following figure selected from "The Almond Production Manual," developed by Joe Connell and Richard Snyder, demonstrates the change in sensitivity. Essentially, sensitivity does vary slightly by variety, but a 50% or greater of crop loss can be experienced during bloom when temperatures drop to 27F for 30 minutes. After petal fall, this temperature threshold increases to 28F. Colder temperatures can cause significant crop loss.Implementation of frost protection measures should be considered when temperatures approach freezing as orchards are often colder than forecasted temperatures. Mowing must be done prior to the frost event. Irrigation systems applying water during the night will provide a heating effect even with a wet soil surface due to heat being released off the water as it freezes. In essence, with these systems, more water equals more protection. Targeted amounts of water should be 30-40 gallons per minute per acre. Minimally, water should be applied at rates higher than 15 gallons/minute/acre to avoid freezing of the spaghetti tubing/ irrigation lines.Temperatures are often the coldest an hour or two before dawn. Irrigation systems should be turned on a few hours before the expected coldest period. Make sure pumps are checked prior to expected frost event to make sure they are working.