January Thaw (again)

It's "January thaw" time in North Carolina, the current temperature is 67F (19.4C). So growers and researchers are worried. Will blackberry buds be breaking?

For those of you that were in Savannah last week, both John Clark and I discussed chilling models. John described the Utah Model ( models 5 and 6 below are variations of the Utah model), that assigned partial ceiling units and subtracted units. I discussed a simpler model (model 2) that just accumulated chill units when the temperature was between 32-45 F and the starting date occurred when temperatures were below 28F.  See the tables at the end of this post for all the details.

Based on the data collected so far this winter by the State Climate Office of North Carolina, we have somewhere between 259-420 chilling hours in Raleigh. We usually get around 800 units, because we are well below 800, buds should remain dormant. However, in the western part of the state, chilling units are higher and a lengthy warm spell may stimulate some buds.

Here are some chill units that have accumulated so far around the state.

Location (CRONOS)	Blueberry model	Blackberry model 1	Blackberry model 2	Blackberry model 5	Blackberry model 6
Raleigh (LAKE)	832	406	259	420	375
Salisbury (SALI)	978	788	517	727	612
Lincolnton (KIPJ)	953	692	433	631	537
Hendersonville (BEAR)	NA	923	512	782	627
Castle Hayne (CAST)		315	195	212	171

You can calculate your chilling units near you at this site State Climate Office of North Carolina Model 2  (it also can calculate for stations in  GA, KY, MD, NC, SC, TN , VA, WV).

If you would like me to look up chilling units for other models for your area, send me an email. Gina_Fernandez@ncsu.edu.

http://climate.ncsu.edu/cronos/blackberry

Details of all the chilling models.

NCSU Blueberry Model

Temperature	Units of chilling
< 45°F (7.2 °C)	1
45-55°F (7.2-12.8 °C)	0.5
55-65°F (12.8-18.3 °C)	-0.25
>65°F (18.3 °C)	-1.0

The model begins when it has a positive balance that is not negated by warmer weather. Once 800+ chill hours have accumulated, points are no longer negated for temperatures 55° and above. The model ends February 28 at midnight. 

Blackberry model 1

Temperature	Units of chilling
<44.6°F (7.2°C)	1

Starts when hit 28°F for the first time in the fall.

Blackberry model 2

Temperature	Units of chilling
32-44.6°F (0-7°C)	1

Starts when hit 28°F for the first time in the fall.

Blackberry model 5

Temperature	Units of chilling
32-48.38°F (0-9.1°C)	1
48.5-54.3°F (9.2-12.4 °C)	0.5
54.5-60.6°F (12.5-15.9°C)	0
60.8-64.4°F (16-18°C)	-1

Starts when hit 28°F for the first time in the fall.

Blackberry model 6

Temperature	Units of chilling
34.7-36.3°F (1.5-2.4°C)	.5
36-48°F (2.5-9.1°C)	1.0
48.5-54.3°F (9.2-12.4°C)	.5
54.5-60.6°F (12.5-15.9°C)	0
60.8-64.4°F (16-18°C)	-.5
>66°F >18°C)	-1

Starts when hit 28°F for the first time in the fall.

Utah Chill model

Temperature	Units of chilling
<34.5°F (1.4°C)	0
34.6-36.4°F (1.5 – 2.4°C)	.5
36.5-48.4°F (2.5- 9.1°C)	1.0
48.5-54.4°F (9.2-12.4°C)	0.5
54.5-60.6°F (12.5-15.9°C)	0
60.8-64.4°F (16-18°C)	-.5
>64.5°F (18°C)	-1.0