Gordon Johnson, Extension Vegetable & Fruit Specialist; firstname.lastname@example.org
It is time to clean up strawberries in both plasticulture and matted row systems. Start by taking off floating row covers. Place to the side for future frost protection. In matted row systems, rake any straw mulch to the side of rows to uncover plants.
Remove any dead leaf materials and dispose of away from the strawberries. Gray mold of strawberry fruit is caused by the fungus Botrytis cinerea. The reservoir for this fungus is mycelium in dead strawberry leaves. This mycelium becomes active in the spring and starts to produce spores on the old leaf tissue, which then spread to blooms. Most infections start at the bloom stage, but symptoms usually do not develop until close to harvest (the fungus does not become active until the fruit enlarges).
This pathogen can also cause crown rots that can weaken or kill plants. The crown rot phase of the disease often develops under floating row covers that are used to promote growth or protect against cold events.
Removal of dead leaves will go a long way to reduce gray mold. Fungicide programs also should begin at this time, especially if Botrytis was present under the covers. Use Captan or Thiram fungicides prior to bloom.
Mites can also be an issue under row covers and should be scouted for. Miticide applications should be made as necessary.
Winter annual weeds such as chickweed and henbit should be hand weeded from strawberry holes in plasticulture. An asparagus knife can help to “cut” weeds out where they are close to the mother plant. Weeds will impact yield if not removed promptly. In addition, weedy fields stay wet longer, and Botrytis gray mold loves that moisture.
Several herbicides are labeled for row middles between plastic. For dormant matted row systems, herbicides such as 2,4-D amine may be used over the top (do not use in plastic systems). See the Mid-Atlantic Commercial Vegetable Production Recommendations for specific recommendations (pp. 365-366) https://www.udel.edu/content/dam/udelImages/canr/pdfs/extension/sustainable-agriculture/BFP_2022-2023_Strawberries.pdf
Flowering and Frost/Freeze Protection
As temperatures warm, remove row covers to keep strawberries from flowering too early. Removing row covers during warmer winter periods can help to delay bud activity and reduce susceptibility to freezes. 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 or early fruiting stage. Another issue is that pollinating insects are restricted with covers, resulting in smaller fruit size if covers are left on too long. Flowers that open under row covers are often deformed or small. Once flowering occurs, use row covers for frost and freeze protection. Put covers back over strawberries when frosts or freezes are forecast.
Advective freezes occur with freezing temperatures and high winds. This is the most difficult to protect against. For strawberries, two layers of floating row covers may be the most effective strategy for advective freezes. Double covers have been shown to be more effective than single heavy covers in this case. Irrigation along with double covers can provide even more protection if done properly.
Radiation (or radiant) freezes occur on cold, still nights. In this case cold air is near the ground and warmer air is above. Row covers in strawberries will protect against radiation freezes too.
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.