Warmer Weather Is Needed! (Sat., 3/9/13)

— Written By

In this advisory:

A. Heavy frost is likely in many areas tonight and tomorrow morning

B. Some thoughts on crop ripening in 2013 compared to 2012

—————

A. Heavy frost at Clayton tomorrow morning:  First things first, I got this advisory from SkyBit for Clayton Central Crops for tomorrow just a few minutes ago. It is expected that this will be a heavy frost in the morning. Clearly, if you are dealing with a crop that is in bloom, you better take protective measures if you receive an advisory like this one!

E-WEATHER FROST/FREEZE ALERT
Issued: 03-09-2013 at 13:58

Site Name: NCCLY
Geophysical Location – Lat(D):  35.6506 Lon(D):  78.4567 Elev(ft):   439

GENERAL SUMMARY
Weather conditions are favorable for a FROST in your area.
Please see details below.

DESCRIPTION OF EVENT

Date of Event:     03-10-2013
Type of Event:     FROST
Severity of Event: HEAVY
Extent of Event:   WIDESPREAD

You can see from the AWIS map below that it will be one of those very borderline nights across much of the state, and any areas in dark blue are most likely for FROST tomorrow morning.

NC min Sun.nc.2

Figure 1. Minimum temperature map for NC for Sunday morning – dark blue areas could have a hard frost tonight which could be very dangerous to plantings in open bloom and popcorn stages.

Here is the more detailed AWIS Frost/Freeze Forecast for NC tomorrow morning:

AWIS Weather Services, Inc.
North Carolina Frost/Freeze Forecast
Produced at  506 AM CST on Sat Mar  9 2013

… Forecast for Tonight …

Northeast NC Coast
Currituck/Camden/Pasquotank/Tyrrell Counties

**** NEAR FREEZING COLD LOCATIONS  ****
****  FROST LIKELY ****

Lowest Temperatures:      35 – 41
Elizabeth_City Min          36
Range Dewpoint Temps:     29 – 37
Range Wetbulb  Temps:     33 – 43
AVG Wind Direction/Speed:  NE  6
AVG Sky Condition:         Clear

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

03/11/13  03/12/13  03/13/13  03/14/13  03/15/13  03/16/13
——–  ——–  ——–  ——–  ——–  ——–
40 – 48   52 – 58   40 – 46   36 – 42   32 – 41   40 – 46
——–

East Central/SE NC Coast
Carteret/Pamlico Counties

**** NEAR FREEZING COLD LOCATIONS  ****
****  FROST LIKELY ****

Lowest Temperatures:      33 – 37
Morehead_City Min           37
Range Dewpoint Temps:     31 – 37
Range Wetbulb  Temps:     33 – 43
AVG Wind Direction/Speed:  NE  4     Long Periods of Calm
AVG Sky Condition:         Clear

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

03/11/13  03/12/13  03/13/13  03/14/13  03/15/13  03/16/13
——–  ——–  ——–  ——–  ——–  ——–
44 – 46   55 – 56   43 – 45   36 – 39   31 – 37   42 – 45
——–

Southeast NC
NWS FORECAST ZONES 87-90,96-101

**** NEAR FREEZING COLD LOCATIONS  ****
****  WIDESPREAD FROST   ****

Lowest Temperatures:      33 – 37
Elizabethtown Min           35
Range Dewpoint Temps:     29 – 38
Range Wetbulb  Temps:     34 – 45
AVG Wind Direction/Speed:   E  3     Long Periods of Calm
AVG Sky Condition:         Clear

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

03/11/13  03/12/13  03/13/13  03/14/13  03/15/13  03/16/13
——–  ——–  ——–  ——–  ——–  ——–
42 – 48   54 – 58   37 – 46   36 – 40   34 – 38   42 – 46
——–

North-Central NC
Franklin County Area

**** FREEZE COLD LOCATIONS  ****
****  WIDESPREAD FROST   ****

Lowest Temperatures:      31 – 39
Louisburg Min               32
Durations at/below 32:     0 –  1
Range Dewpoint Temps:     29 – 34
Range Wetbulb  Temps:     33 – 43
AVG Wind Direction/Speed:   V  2     Long Periods of Calm
AVG Sky Condition:         Clear

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

03/11/13  03/12/13  03/13/13  03/14/13  03/15/13  03/16/13
——–  ——–  ——–  ——–  ——–  ——–
39 – 46   49 – 55   33 – 41   30 – 37   32 – 40   35 – 42
——–

North/Central NC
Alamance County Area

**** FREEZE COLD LOCATIONS  ****
****  WIDESPREAD FROST   ****

Lowest Temperatures:      32 – 38
Graham_AG Min               36
Durations at/below 32:     0 –  0
Range Dewpoint Temps:     26 – 33
Range Wetbulb  Temps:     33 – 42
AVG Wind Direction/Speed:  SE  3     Long Periods of Calm
AVG Sky Condition:         Clear

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

03/11/13  03/12/13  03/13/13  03/14/13  03/15/13  03/16/13
——–  ——–  ——–  ——–  ——–  ——–
41 – 46   49 – 55   34 – 39   32 – 37   34 – 40   37 – 42
——–

South/Central NC
Richmond County Area

**** FREEZE COLD LOCATIONS  ****
****  WIDESPREAD FROST   ****

Lowest Temperatures:      32 – 37
Ellerbe Min                 35
Durations at/below 32:     0 –  0
Range Dewpoint Temps:     29 – 35
Range Wetbulb  Temps:     34 – 44
AVG Wind Direction/Speed:  SE  3     Long Periods of Calm
AVG Sky Condition:         Clear

Extended Forecast: Range of Lowest Min Temperatures in the Above Zones
Min Temps Valid For Morning of Given Date (May NOT include ALL cold pockets)

03/11/13  03/12/13  03/13/13  03/14/13  03/15/13  03/16/13
——–  ——–  ——–  ——–  ——–  ——–
42 – 46   49 – 56   35 – 43   34 – 38   34 – 38   39 – 44
——–

For more detailed information visit www.awis.com or call 888-798-9955.
Copyright 2013 AWIS Weather Services, Inc. All rights reserved.

For minimum temperatures in your city/town in NC, please click here:NC Min Temp

B. Some thoughts on crop ripening in 2013 compared to 2012: 

Unless stressed by other environmental factors, the development rate from strawberry dormancy to bloom stage, and then to berry harvest,  depends upon the daily air temperature. In both December 2012 and January of 2013 we had some surprisingly warm temperatures that forced some winter bloom activity, as was evident in a Chandler planting we toured on the Strawberry Walk in VA Beach, 2/25/13 (Figure 2), but temperatures have remained so cool in recent weeks that many growers are now wondering if we may now be on track to a more “traditional” berry ripening season in spring 2013 compared to last year when the crop was nearly 2 weeks early! During the Field Walk in VA Beach, Amanda Baker (Figure 3) reminded us that they were actually underway with their harvest last year on Easter weekend (April 7-8).

assess plant growth blooms

Figure 2. In the upper left you can see a smaller Chandler plant that had some “winter blooms” that were killed by Feburary freezes in VA Beach. It was a warmer January this year in VA Beach than last year, and the Growing degree units accumulated in Jan 2013 were 51.5 compared to 26.5 in Jan. 2012. However, in February of this year only 12.5 GDUs accumulated vs. 50 in Feb. 2012, thus the total GDUs for Jan-Feb 2013 (64) compares to 76.5 in 2012 for this same period. March continues to be very cold, and”0″ units accumulated from March 1-8, 2013!

amanda baker

Figure 3. Amanda Baker, Brookdale Farm, addresses a group at the Virginia Field Walk on Feburary 25, 2013. Amanda mentioned they were picking last year on Easter weekend (April 7-8). By April 2nd (2012), this location in Virginia Beach had accumulated about 370 GDUs (this was when a few berries were getting ripe).

More about crop stages and GDUs:

Because many developmental events of plants and insects depend on the accumulation of specific quantities of heat, I have been very interested in the last few years in trying to predict when say strawberries will be in bloom, and then harvest based on daily air temperatures. Growing degree days (GDD), or Growing degree units (GDUs)  take into account the number of temperature degrees above a certain threshold temperature, which varies among crop species, but for strawberries a base temperature of 50 F is commonly used. The base temperature is the temperature below which plant growth is negligible. Arguably, there can be significant strawberry root development even in the mid-40s, but we do know that floral development is inhibitied at temperatures below 50 F, and so I believe that 50 F is a reasonable base temperature to consider in strawberries. In strawberries, I have been interested in knowing the Growing degrees (GDs) above a threshold base temperature of 50 F that may be associated with 5% bloom, 50% bloom, the beginning of harvest and when we might expect a peak harvest period.

Calculation:  GDs are calculated each day as maximum temperature plus the minimum temperature divided by 2 (or the mean temperature), minus the base temperature. GDUs are accumulated by adding each day’s GDs contribution as the season progresses.

GDUs = (T max + T min)/2 – T base (50 F)

Example caculation:  the forecast for tomorrow (March 11th)  in Nashville, NC, is for a  High 71 F, and Low 56. Thus, we will accumulate 13.5 Growing degree units { (71 + 56)/2 = 63.5 – 50 F = 13.5 F}.

What is very interesting to look at presently is how many GDUs will accumulate over the next 15 days, and then compare this to last year when we had such an exceptionally warm month of March.

Table 1. GDU Forecast for Nashville, NC (AccuWeather Pro), March 9-23, 2013.

Sky Date high low ave base 50 net GDU
clear Sat-Mar 9 61 32 46.5 50
mostly clr Sun-Mar 10 65 31 48 50
mostly clr Mon-Mar 11 71 56 63.5 50 13.5
showers Tue- Mar12 67 37 52 50 2
clear Wed-Mar13 61 33 47 50
clear Thur-Mar14 57 36 46.5 50
clear Fri-Mar15 63 39 51 50 1
clear Sat-Mar16 57 44 50.5 50 0.5
clear Sun-Mar17 73 41 57 50 7
clear Mon-Mar18 52 44 48 50
showers Tue-Mar19 64 45 54.5 50  4.5
clear Wed-Mar20 53 46 49.5 50
clear Thur-Mar21 60 48 54 50 4
clear Fri-Mar22 63 44 53.5 50 3.5
showers Sat-Mar23 55 47 51 50 1
37

What is quite shocking is to realize that for this same period last year that we picked up 203 GDUs (Table 2), or nearly 5 1/2 times the heat accumulation that occurred for this same 15 day period in 2012.

Table 2 March 9-23 GDUs for Nashville, NC, for a 6 year period
Base 50 F
Year GDUs
2013 37 (projected)
2012 203
2011 106
2010 75
2009 47.5
2008 67
Average 89.3

What is even more interesting to note is that by March 14th last year a grower in the area of Nashville, NC, was already seeing lots of new blossoms, and on this date the grower recorded 8-12 open blossoms on Chandler and 10-16 open blossoms on Camarosa. Arguably, for the Chandler plants this might have been the 10% bloom stage if you conside that the average Chandler plant had about 75 blossoms in total (8/75 = 10.6). This same grower recorded 12-26 blooms on Chandler plants that had been under covers for the period from about March 2-14, and 12-32 open blossoms for Camarosa under covers for this same period (we had a big freeze in early March 2012, and this particular grower applied row covers on one field, and used sprinkling for the field with the lower bloom counts).

Realzing that it is now past 4pm on Saturday, March 9, and that we have a frost coming in the morning, I am going to conclude today’s advisory with these comments:

  • THE HEAT ACCUMULATION (IN GDUs) LAST YEAR FOR THIS NASHVILLE LOCATION FOR JANUARY AND FEBRUARY WAS 84 UNITS, AND THIS YEAR IT WAS 92 UNITS. SO NOT MUCH DIFFERENCE.
  • HOWEVER, WHAT IS MOST INTERESTING IS WHAT HAS HAPPENED SINCE THE BEGINNING OF MARCH IN 2013 COMPARED TO LAST YEAR. FOR THE FIRST 8 DAYS OF THIS MONTH WE DID NOT LOG EVEN 1 UNIT! LAST YEAR, THIS LOCATION LOGGED 37.5 GDUs for this period.
  • If you look at Table 1 again, please note we anticipate only getting 15.5 GDUs from March 9-14 this year (for the period of March 9-14, 2012, this location had another 37.5 GDU’s, or a total of 165 GDUs from Jan. 1-March 14 — when there were 8-12 open Chandler blossoms).
  • I am projecting only about 107 GDUs this year since Jan. 1 (through March 14) for this location compared to 165 last year. But, what is a little worrisome is that from March 15-March 23, this same location will only pick up 22 GDUs (if AccuWeather is correct) – see Table 2.
  • Thus, only about 2.4 GDUs will be accumulated each day (for the 9 day period), and this is only a small fraction of the heat accumulation that was occurring in mid-March of last year!
  • On April 2, 2012, I visited this particular farm near Nashville, NC, and on that date the GDUs accumulated since the beginning of the year (Jan 1-March 31), were 416 GDUs compared to 200 in 2011.
  • Medium weight row covers of 1-1.2 oz per sq yd may “bump up” plant temperatures beneath the covers on SUNNY days, but unless the daily highs will be at least in the mid-to-upper 50s, the benefit of having row covers “on” is negligible to plant growth.
  • REMEMBER, WE ARE ASSUMING THAT AN AVERAGE  TEMPERATURE OF 50 F IS REQUIRED FOR STAWBERRY PLANT GROWTH, SO WE WOULD NOT EXPECT ANY REAL BENEFIT FROM HAVING COVERS ON THE CROP WHEN AVERAGE DAILY TEMPERATURES ARE BARELY REACHING 50
  • And, the reason I say this is that I went back an reviewed some data from a NCSU study done in Plymouth NC in 1996 and 1997 by Dr. Gina Fernandez that was reported in HortTechnology in July-September 2001, and from the data presented in Table 3 on p. 443 (daily highs, lows and means for treatments with and without row covers during the first 2 weeks of November) it turned out that having a row cover added about 2.4 GDUs for 2 weeks in Nov of 1996, but in reviewing the data set for Nov of 1997, the row covers did “bump up” the GDU’s by 15.8 GDUs (base 50 F).
  • Row Cover Plots in Fall 1997, Plymouth, NC (1.2 oz cover)
    Nov-97 max min mean GDUs
    1 70.52 70.52 70.52 50 20.52
    2 67.82 65.48 66.65 50 16.65
    3 61.34 57.56 59.45 50 9.45
    4 57.74 53.78 55.76 50 5.76
    5 54.32 50.18 52.25 50 2.25
    6 61.16 54.86 58.01 50 8.01
    7 60.98 55.58 58.28 50 8.28
    8 59.54 54.68 57.11 50 7.11
    9 57.38 53.24 55.31 50 5.31
    10 52.7 51.98 52.34 50 2.34
    11 55.04 53.24 54.14 50 4.14
    12 58.1 52.34 55.22 50 5.22
    13 51.26 46.4 48.83 50 -1.17
    14 48.74 41.36 45.05 50 -4.95
    58.3 54.4 56.4 95.04
  • Plots with No Covers in Fall 1997, Plymouth, NC (1.2 oz cover)
    Nov-97 max min mean GDUs
    1 70.7 70.16 70.43 50 20.43
    2 64.22 68.36 66.29 50 16.29
    3 58.82 57.56 58.19 50 8.19
    4 54.68 54.86 54.77 50 4.77
    5 51.26 51.26 51.26 50 1.26
    6 57.38 54.68 56.03 50 6.03
    7 57.92 54.14 56.03 50 6.03
    8 56.84 52.52 54.68 50 4.68
    9 54.68 53.06 53.87 50 3.87
    10 52.34 51.62 51.98 50 1.98
    11 53.78 52.52 53.15 50 3.15
    12 54.32 50.72 52.52 50 2.52
    13 48.74 43.7 46.22 50 -3.78
    14 43.7 40.1 41.9 50 -8.1
    55.7 53.9 54.8 79.2

Summary

We still have “so much more” to learn about using GDUs with strawberries in our part of the world, but from an analysis of GDUs this season vs. last, it is quite obvious that we are in  much colder season this year, and for this reason we are anticipating later calendar dates for bloom and harvest than 2012. In reviewing the expected GDUs for Nashville, NC over the next 15 days, for example, it is very interesting to see that we may add  only add about 37 GDUs from March 9-23, 2013. In 2012,  203 GDU’s were accumulated in this same 15 day period — that is less than 20% of the GDU’s accumulated last year for this period.

Row covers applied now will help to advance crop ripening and may also slightly improve overall  yields (later in the season), but there is no experience or experimental data to guide us at this time on how best to approach this “opportunity”?

In a fall season in a trial done in Plymouth, NC, in 1997, it was possible to add about 16 GDUs for the period from Nov 1- Nov 14 by having row covers “on” during this entire period. But, in another year (1996), they added only about 2.4 GDUs for a 2 week period. In a closer examination of the Nov 1997 data, it was interesting to note that when daytime highs were going to be in the mid-to-upper 50s, the covers were able to elevate the temperature (beneath the cover) by several degrees F above the ambient temperature, but when daytime highs are only going to be in the upper 40s or low 50s, then it is simply too cold to add GDUs.

There may be an opportunity to get this crop out of its “creeper gear” and add some GDUs  by having covers “on” on days over the next 2 weeks when the forecast is for highs in the mid-to-upper 50s and 60s. I am not concerned about too much heat from the row cover application as there will be only one day (March 17) with daytime highs in he mid-70s — that will not present a problem. Its when it gets into upper 70s and 80s that I become very uneasy about having row covers “on” at this time of year.

Checking in with another crop advisor up in MD – Bob Rouse

I enjoyed being able to check in with Bob Rouse yesterday up in MD about this whole idea of leaving covers on during a period when the strawberry crop is stuck in a creeper gear, and I think we both agreed that no general recommendation can be made. Each grower must decide what may be best to do at this point based on their location and individual circumstances. I know that many of you are “locked in” to trying to have berries as early as possible, and where earliness is quite critical, then having covers on during the next few weeks makes a lot of sense. The covers will advance the crop for sure, but you will need to be very careful to get the covers off once the crop is in bloom. According to Bob Rouse, it is not uncommon for producers in the Mid-Atlantic region to leave the covers on all the way up to the “popcorn” stage (just before open blossoms). But, the covers must come off once its reached blooms, as the covers will definitely interfere with insect and wind pollination.

It’s a Goldilocks forecast for the next 2 weeks!

The weather forecast for the next 2  weeks would appear to be “favorable” for continuous row cover use – if you are thinking about trying this on some of your crop. It (the weather) will be neither  too cold or too warm for covers. It is whate   Bob Rouse said to me yesterday is a, “goldilocks forecast.”  Meaning its neither too hot or too cold!

Russ row cover

Dr. E. Barclay Poling
Professor Emeritus/Extension Strawberry Specialist
Department of Horticultural Science
Campus Box 7609, 162A Kilgore Hall
NC State University
Raleigh, NC 27695-7609
919-418-9687 (Cell)
919-515-2505 (Fax)
barclay_poling@ncsu.edu
https://strawberries.ces.ncsu.edu

Written By

Photo of Barclay Poling, N.C. Cooperative ExtensionDr. Barclay PolingFormer Professor and Extension Specialist, Strawberries and Muscadines (919) 515-5373 (Office) barclay_poling@ncsu.eduHorticultural Science - NC State University
Updated on Apr 24, 2013
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