Use Caution With Irrigation Shut-Down Times This Morning (7:15am, Sunday, 3/5/17)

— Written By Barclay Poling
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Figure 1. Sunrise in China Grove, NC (March 5, 2017). This grower has been using sprinkler irrigation to protect his strawberry crop – last night was the 3rd night in a row of sprinkling! In this location the wet bulb temperature of 33 F will not be reached until 10:30 a.m. (Salisbury-Rowan, NC AWIS Hourly Forecast).

Figure 2. At 8 a.m. it was 22 F outside the row cover and 34 F underneath (Moseley, VA). Using irrigation with row covers was essential at this location with temps in low 20s. A row cover alone would not be sufficient protection! Yes, it is a great idea to double up on covers when temps are heading into low 20s at bloom, but not all growers have that option. Fortunately, this grower and his helpers, will be able to shutdown soon this morning and go to bed — they might want to enjoy some hot soup has well! Technically, you are ok to shut down with blossoms reading 32-33 on digital thermometer, but with winds and dropping dew points, you want to make sure things don’t go in reverse. I am guessing that by maybe 9 a.m. (with the sun shining brightly on top of the ice covers), that the blossom temps beneath will  be up around 38-40 F by 9 a.m.? What is really quite interesting is to look at the SkyBit for this location, and note in bottom table that the wet bulb of 33 F will not be reached until 2 p.m., so that’s about 5 more hours of sleep for the grower using row covers in conjunction with sprinkling. The SkyBit for farm is at bottom of advisory. Oh, I just heard now from grower and they are shutting down at 8:45 a.m. One more night of cold protection tonight, and then covers coming off Tuesday or Wed (whenever it is dry enough!).

Good morning,

I have received several reports from growers this morning from different parts of Southeast, including right here in Virginia where I now live (Williamsburg). The thing that has really “struck me” about last night and now this morning are the very low dew points. We had a low of about 25 F here this morning, and never saw any “white frost.”  No wonder! At 7 a.m. the dew point was 16 F, and its going down! AWIS shows that Williamsburg will see dew points in single digits by 11 a.m. Also, there will be light winds this early morning to go along with dropping dew points. THIS COMBINATION OF DROPPING DEW POINTS AND WINDS CAN BE LETHAL TO YOUR STRAWBERRY CROP. CONDITIONS ARE IDEAL “EVAPORATIVE COOLING” – THIS PHENOMENON CAN CAUSE THE TEMPERATURE OF A BLOSSOM TO “DROP AFTER SUNRISE” BELOW ITS CRITICAL TEMPERATURE! Believe me, that is something you don’t want to do! Of course, if you have been using row covers (alone), you do not need to be concerned about evaporative cooling, but you do need to leave those covers in place as there will likely be one more night of this!

For growers using sprinkler irrigation, it is important to double-check these tables below to see when the WET BULB temperature will be rising to 33 F today (I normally say morning, but some areas may need to run past noon time – sorry about that). Of course, if you are sprinkling on top of covers, then you will let your digital thermometer and thermocouple inserted in the blossom dictate when it is safe to stop watering. I think those growers will be pleasantly surprised to learn how much sooner they can safely shut down than growers who are using sprinkling alone.

Getting some practice consulting wet bulb temps:

Example:  So,  if you are not accustomed to consulting hourly forecast tables for wet bulb temperature information, then, for practice,  please click on Salisbury-Rowan, NC, and you will see that at 7 a.m. the temperature was about 27 F, but the wet bulb was down around 25 F. The wet bulb needs to reach 33 F for safe shut down, and that should happen between 10 a.m. (Air = 39 WB=32) and 11 a.m. (Air =42 WB=34).

Another example over in Chesapeake VA:

Unfortunately, for my VA grower friends over in Chesapeake this morning (where we had the Field Walk last week), the dew point is dropping this morning (like Williamsburg), and the wet bulb of 33 F will not occur until mid-afternoon! This is indeed a very strange situation! But, if you look at the Hourly Forecast for Chesapeake (click on Chesapeake-Ches, VA), you will see that dew points are dropping today and winds are increasing! Low dew points and winds DRIVE evaporative cooling. Hopefully,  most of these growers are using row covers and not relying on sprinkling alone? The low over there this morning was about 26 F (row cover is perfect for this type of situation).

So, please be sure to consult the AWIS Hourly forecast for the city/town closest to you to see when the wet bulb temperature of 33 F will be reached this morning, or afternoon!

Unfortunately, we still have one more night of this to go! (Report coming out next)

North Carolina


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



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



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

South Carolina


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



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



Bowling_Green Covington Danville-Powell_ Fort_Campbell
Fort_Knox/Godma Frankfort_AP Glasgow_KY Henderson_City
Jackson_KY Lexington_KY London_Corbin Louisville_AP
Louisville/Bowm Middlesboro_AP Monticello_KY_AP Murray_AP
Owensboro_AP Paducah Richmond_Madison Somerset(AWOS)

SkyBit for Farm shown in FIG 2