Over the weekend we are anticipating a classic “advective freeze” event, which does not bode will for southeastern fruit growers. An arctic air mass is moving across the country that is projected to affect the entire eastern portion of the country. With it, daytime conditions may be cool to cold, cloudy to clear and windy. At night, temperatures will continue to drop and the wind will continue to blow. Advective freeze conditions may persist for more than one day. With an advective freeze, the ability to protect crops is very limited.
The level of damage to various small fruit and tree fruit crops is dependent upon the physiological growth stage they’re in at this time. As buds progress from dormancy to bloom, they become more sensitive to cold damage and the gap between minor damage and severe damage narrows. Buds on healthy plants are somewhat more tolerant of cold than on stressed plants. Conditions leading up to the cold event, the duration of the cold event and the severity of the cold will all impact the actual amount of bud damage received. The critical temperatures for bud kill vary for different crops.
Additionally, the relatively sudden change from warm weather to cold and the magnitude of the temperature drop are significant factors and could result in greater damage than if temperatures over the past few days had been lower. Many homeowners have contacted me asking what they can do to protect their crops, but protecting crops during an advective freeze event is difficult and the options are few.
Active control techniques often associated with radiation frost events are worthless in an advective freeze. With the absence of an inversion layer, plus the presence of high winds, heating, frost blankets, and wind machines are not viable options. Furthermore, using irrigation to “ice down” plants likewise is not advisable during an advective freeze. The wind will distort discharge patterns from emitters resulting in erratic coverage. Failure to continuously wet an area will result in evaporative cooling of the wetted surface. If this occurs, the actual temperatures that the plant is exposed to will drop below air temperatures, resulting in greater damage than if nothing had been done.
If the weather forecasts are even close to being accurate, the ability to protect crops is virtually non-existent. The stage of bud development on your crops will give some idea as to what kind of damage may occur. This type of weather is not necessarily unheard of for early March, and additional cold events this spring certainly can occur. If such events are in the form of radiation frosts, several things can be done to lessen the potential for damage. For example, in some crops, such as grapes, delayed pruning may be beneficial in that it can delay bud development in the desired fruiting zone of the vine for spur-pruned vines.
Anticipate future cold events. While a spring frost is not a certainty, their frequency is great enough to merit preparation. Radiation frosts are more common than advective freezes. There are several things that can be done in anticipation a radiation frost. Maximize air drainage from the site by removing grown up fencerows, cleaning up ditch banks and by closely mowing between rows and around the outside of the planting. Do not cultivate soils. If soils are dry, irrigate a few days in front of a predicted cold event. If you have active frost control techniques, make sure they are operational prior to needing them.