Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Row cover management in plasticulture strawberries has been difficult this year due to the mild winter. In normal winters, row covers applied in December serve as winter protection to limit stand losses, dessication damage, and low temperature damage to buds. While plants are in a dormant state or when buds are not yet active in strawberries, the buds can tolerate temperatures down to 10°F.
Removing row covers during warmer winter periods can help to delay bud activity and reduce susceptibility to later freezes. Replace row covers in times when freezes are expected. Highest yield potentials are usually obtained by uncovering and covering in the late winter and spring based on expected temperatures when compared to the practice of keeping row covers on continuously into the flowering stage.
Once buds have begun to emerge, even when tight, they can only tolerate temperatures down to 22°F. As they begin to open, the critical temperature for damage increases (popcorn stage 26°F, open blossom 30°F).
For growers that have not been taking row covers on and off and will be leaving them on until bloom, the potential for losses due to freeze events will be greater during March due to the increased bud activity. Prior to forecasted freeze events, check the plant bud stage, and apply additional freeze production to limit losses. This may include double covering with row covers (2 layers), or the use of low volume sprinklers through the night and into the morning as a frost protection over the row covers. Loss of buds or flowers due to freeze events will reduce yields and profits substantially. A single 1.2 ounce floating row cover will give about 4 degrees of protection.