Reviewing Growing Degree Day Accumulations at Clayton

— Written By Barclay Poling
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chan with coverFig. 1. It was rather shocking to see this many open blossoms on Chandler yesterday on a farm north of Greensboro, NC. With the usual interval of 30 days from open bloom to harvest, this crop of Chandler plugs that had row covers this winter could be ready for harvest in mid-April.

Dear Agents, Agronomists and Growers,

I know we’ve all been observing the rather spectacular advance of this year’s strawberry crop since last Monday, March 7.

These are the daily Growing Degree Day accumulations at Clayton since March 1st:

gdd from march 1Fig. 1. Daily Growing Degree Day Units since March 1st. With many recent days approaching 20 GDDs per day, and yesterday exceeding 22 GDD units, it is no wonder we are seeing such rapid changes in the strawberry crop since 3/1/16. At this time of year it is more common to see GDD numbers in he single digits (not upper teens and low 20s).

Believe it or not, we also saw this kind of heat accumulation occur back mid-to-late December:

chart of growing degree daysFig. 2. Note the remarkable GDD units experienced back in mid-to-late Dec at Clayton Central Crops. That warm spell triggered blooms at Christmas in Camarosa as well as some other early varieties. THOSE BLOOMS DIED, OF COURSE, BUT LEFT GROWERS WITH ANOTHER PROBLEM…BOTRYTIS INOCULUM GALORE (FIG. 3).

inoculumFIG. 3. BOTRYTIS INOCULUM (3/14/16) ALL OVER THE DEAD BLOOMS AND PEDICELS OF A STRAWBERRY PLANT THAT WENT INTO AN EARLY BLOOM BACK IN DEC 2016. THESE WERE SUBSEQUENTLY WINTER KILLED, AND NOW SERVE AS A VERY NICE SOURCE OF INOCULUM.

In case you are wondering, here is the

STANDARD FORMULA FOR CALCULATING GROWING DEGREE DAYS:

TAKE THE DAYS HIGH AND THE DAYS LOW TEMPERATURE ADD THEM TOGETHER AND DIVIDE BY 2. SO IF THE HIGH FOR THE DAY IS 70F AND THE LOW WAS 50F THAT GIVES US A TOTAL OF 120 DIVIDED BY TWO EQUALS 60.

OUR BASE TEMPERATURE FOR THE STRAWBERRIES IS 50F. YOU NOW SUBTRACT 50 FROM 60 AND GET 10 GDD.

USING THIS FORMULA, YOU CAN DETERMINE THAT YESTERDAY (MARCH 16) WE ACCUMULATED 22 GDD UNITS AT CLAYTON:

EXAMPLE:

MARCH 16TH:  MAX =85.1, MIN=59

SO, 85.1 + 59 = 144.1

DIVIDE BY 2 = 72.05

SUBTRACT BASE 50 FROM AVG:  72.05 – 50 = 22.05 GDD UNITS

Date/Time of ob Max Temperature Min Temperature
at 2m (F) at 2m (F)
03/10/2016 78.8P 57.9P
03/11/2016 81P 64P
03/12/2016 76.5P 56.7P
03/13/2016 76.6P 59.4P
03/14/2016 77.2P 61.7P
03/15/2016 76.8P 56.3P
03/16/2016 85.1P 59P

AS OF TODAY (ST PATRICKS) WE HAVE NOW ACCUMULATED A TOTAL OF 213 GDD UNITS; AS OF LAST FRIDAY (3/11) WE HAD 143 UNITS. WHEN YOU REACH ABOUT 450 UNITS, YOU CAN EXPECT TO BE DOING SOME PICKING!

JAN FEB MARFIG. 4. GDD UNITS THIS YEAR AT CLAYTON:  7.9 IN JAN; 60.7 IN FEB; AND 144.9 FROM 3/1-3/16. TOTAL = 213.5.

POTENTIALLY, CLAYTON WILL REACH 398 GDDs on April 14th (few ripe) and by April 19th it will be at 456 GDDs (light pick) and over 500 by April 22 (full picking).

gdd accum clayFIG. 5. Cumulative GDDs at Clayton Central Crops using temperature forecast information for this zip code (27520) from AccuWeather. This will definitely change between now and even next week! But, as of today, it does look as if we will be reaching approximatly 400 GDD by mid April, and this is when I would anticipate some light picking. By the following week (around April 21), there should be a relatively full picking.