Cold Protection and Weather Update Follow Up (Fr. Mar. 2, 2018)

— Written By

Good evening,

Barclay and I will tag team the weather forecasts over this season. We have a very early season this year and his experience is most appreciated by me and I’m sure by all of you as well.

When I was visiting Ron Edwards from Spring Farms in SC last week, some plants were in 5-10% bloom already. However, we both decided to wait with fertigation for another week or two, due to the early season and the possibility of cold events. However, if the weather generally stays the way it was the last weeks, some of you in South Carolina and in the eastern plains of North Carolina might consider picking fruit end of March/begin of April.

Here are some advises for you:

(1) Make sure that your market is ready. Have enough labor force/customers to pick the berries.

(2) Make sure not only to watch our weather advisories frequently, but also measure temperatures on blossoms with thermo couples. To learn how to do that, please see: https://strawberries.ces.ncsu.edu/2009/12/mauris-sed-leo-aliquam-aliquam/

As Barclay indicated, your choice to protect your blossoms from cold injury is based on (1) your crop status (pre-bloom or transitioning to bloom?) and (2) the type of cold event (frost, frost/freeze, freeze) (3) temperatures at the blossom.

Table 1 has critical temperatures for cold protection in several stages of plant development. We usually recommend to start protection open blossoms when temperatures are predicted to drop under 35 F.

Table 1: Critical temperatures for cold protection (according to Perry and Poling, 1986)

Stage of Development Critical Temperature (F)
Tight bud 22
Popcorn 26.5
Open blossom 30
Fruit 28

While in the pre-bloom and popcorn stage, row covers are a good protection agains cold, that might be different when your plants are transitioning into open blossom. That is especially the case with early blooming varieties such as Sweet Charlie.

Frost events are based on radiation and often on building of ice crystals, characterized by low wind speeds. Freeze events however are based on moving cold air, weather fronts etc. Freeze events are often characterized by high wind speeds and temperatures below 32 F. Frost/Freeze events have elements of both. The way you protect your blossoms depends on the event and the windspeed. Table 2 gives a good overview of effectiveness and non effectiveness of certain cold protection methods.

Table 2: Cold protection decision tool during bloom

Method Frost Frost/Freeze Freeze
Row Cover effective/very effective effective limited effectiveness
Row Cover + Sprinkler not advised very effective effective
Sprinkler (alone) very effective limited effectiveness no effect

Wind direction and speed is a decisive factor. A good wind prediction tool (and it is for free) is: http://www.windy.com Wind speeds are shown in kts (=1.1 mph) on surface level.

Temperature forecasts:

North Carolina:

Fig.1: Minumum temperatures over the weekend are in the upper 30s in the coastal areas and lower 30s in the plains. 

According to windy.com, wind speed will remain above 10 mph in most regions in NC for the next few days. If you want/need to frost protect, row covers would be more effective than sprinkling, giving the higher wind speeds.

5-DAY hourly forecast:

FORECASTS ARE AVAILABLE FOR THESE LOCATIONS:
Ahoskie-Tri-Cou Albemarle_AP Andrews Asheboro
Asheville_Munic Beaufort-Michae Boone_NC Burlington-Burl
Cape_Hatteras_AG Chapel_Hill-Hor Charlotte Cherry_Point
Clinton_NC Concord_NC Currituck_NC Edenton-Northea
Elizabeth_City Elizabethtown_NC Erwin-Harnett_C Fayetteville_AP
Fort_Bragg/Simm Franklin/Macon_C Gastonia-Gaston Goldsboro_AFB
Goldsboro_NC Greensboro Greenville_AP_NC Hickory
Jacksonville Jacksonville_(A Jefferson_AP_NC Kenansville-Dup
Kill_Devil_Hills Kinston_AP Lexington-David Lincolnton_AP
Louisburg_NC Lumberton_AP_NC Mackall_AAF Manteo/Dare_Co
Maxton Mcalf_Bogue_Fiel Monroe_AP_NC Morganton-Morga
Mount_Airy-Moun New_Bern North_Wilkesbor Oxford_NC
Piney_Island_Bom Pope_AFB Raleigh-Durham Reidsville_AP
Roanoke_Rap_AP Roanoke_Rapids_R Rockingham_NC Rocky_Mount-Wils
Roxboro_AP Rutherfordton Salisbury-Rowan Sanford_NC
Shelby_AP_NC Smithfield_AP Southern_Pines Southport_NC
Statesville-Sta Tarboro_AP Wadesboro_AP Washington-Warr
Whiteville_NC Wilmington_AP_NC Winston-Salem

South Carolina:

5-DAY hourly forecast:

FORECASTS ARE AVAILABLE FOR THESE LOCATIONS:
Aiken_AP Anderson_Co_Air Barnwell_AP Beaufort_Cnty_AP
Beaufort_SC Bennettsville_Je Camden_AP Charleston_Exec_
Charleston_Muni Cheraw_AP Chester_AP Clemson-Clemson
Columbia-Columb Columbia/McEnti Columbia_Metro Conway_AP
Darlington Florence_SC Georgetown_AP_SC Greenville_Donal
Greenville_Down Greenville-Spart Greenwood-Green Hartsville_AP
Hilton_Head_AP Kingstree_AP Lancaster-McWhir Laurens_AP
Manning_AP Marion_AP_SC Moncks_Corner_AP Mount_Pleasant_A
Myrtle_Beach Newberry_AP North_Myrtle_Be Orangeburg-Oran
Pickens_AP Rock_Hill Spartanburg_Down Summerville_AP
Sumter_AP Sumter_SC Walterboro_AP Winnsboro_AP

Georgia:

5-DAY hourly forecast:

FORECASTS ARE AVAILABLE FOR THESE LOCATIONS:
Albany_Municipa Alma/Bacon_Co Americus_AP Athens_Municipa
Atlanta/DeKalb Atlanta/Fulton Atlanta_Intl_Ar Atlanta_Paulding
Augusta/Bush_Fi Augusta_Daniel_F Bainbridge_GA Blakely_AP
Brunswick_GA Brunswick/Glync Canton_GA Carrollton_AP
Cartersville_AP Claxton_AP Columbus_GA Covington_GA_AP
Dalton-Dalton_M Douglas_Muni Dublin/WHBarron Fitzgerald_AP
Fort_Benning Ft_Stewart/Wrig Gainesville_AP_G Greensboro_GA
Homerville_AP Hunter_(AAF) Jesup_AP La_Grange
Lakeland Lawrenceville_AP Macon_AP Marietta
Marietta/Cobb Milledgeville_AP Moultrie_Muni_AP Newnan-Newnan_C
Peachtree_City Rome_GA Savannah Statesboro_GA
Swainsboro_AP Sylvania_AP_GA Thomaston_AP Thomasville_AP
Thomson_GA Tifton_AP Valdosta Valdosta/Moody
Vidalia Warner_Robins_A Washington_GA Washington_GA
Waycross_AP Winder_AP

Virginia:

5-DAY hourly forecast:

FORECASTS ARE AVAILABLE FOR THESE LOCATIONS:
Abingdon Ashland_VA Charlottesville Chesapeake-Ches
Culpeper Danville Dublin/New_Riv Emporia_VA
Farmville Fentress_Naval_A Fort_Belvoir/Da Fort_Eustis/Fel
Franklin/J_B_Ro Hillsville Hot_Springs/Ing Jonesville_AP
Langley_AFB Leesburg/Godfre Louisa-Louisa_C Lynchburg
Manassas_Muni(A Marion/Wythev Martinsville Mecklenburg/Bru
Melfa/Accomack Newport_News Norfolk_Hampton_ Norfolk_NAS
Norfolk_VA Oceana Orange_VA Petersburg_(AWO
Quantico Richlands_AP Richlands_VA Richmond
Richmond_Chester Roanoke Shannon_Arpt Stafford_AP_VA
Staunton-Shenan Suffolk-Suffolk Tappahannock_AP Virginia_Tech_A
Wakefield_AP Wallops_Island Warrenton_Fauqui Washington_Dulle
West_Point_VA Williamsburg_VA Winchester_Rgnl Wise/Lonesome_P

Maryland:

5-DAY hourly forecast:

FORECASTS ARE AVAILABLE FOR THESE LOCATIONS:
Aberdeen Andrews_AFB Annapolis_Naval Baltimore_Sci_Ce
Baltimore/Wash Cambridge/Dorche College_Park_AP Cumberland_AP
Easton_MD Fort_Meade Frederick_MD Gaithersburg_AP
Hagerstown_AP Leonardtown Middle_River Oakland_MD_AP
Ocean_City_AP Patuxent_River Salisbury Stevensville_AP
St_Inigoes/Webst Washington_DC_AP Westminster_AP

Thank you and I hope that helps. Barclay and I will keep you updated.

If you have questions, ask your local extension service or write an email to mark.hoffmann@ncsu.edu

Thanks,

Mark