To determine the air temperature to start or stop sprinklers, first decide what is the critical damage temperature for your crop. Select a wet-bulb temperature that is at or above that temperature. Select the corresponding air temperature from the table. The sprinklers should be started before the air temperature falls below that value and they can be stopped after the air temperature upwind from the protected area exceeds that value. Generally, crop sensitivity to freezing temperature increases from first bloom to the small nut or fruit stages when a crop is most likely to be damaged.
Sensitivity is also higher when warm weather has preceeded a frost night.
All sprinklers in a protection area should be on when the air temperature drops to the temperature selected from Table 1 or 3. This insures that the wet-bulb temperature will be above the critical damage temperature. Sprinklers can be turned off when the air temperature exceeds the value from Table 1 or 3. Then choose the row with the correct dew-point temperature and read the corresponding air temperature from the table to turn your sprinklers on or off. Then find the corresponding dew point in the table.