The number of chilling hours for Georgia peaches are just below last year but above marks recorded in 2018-2019 and 2019-2020, according to the University of Georgia (UGA) Extension peach blog.
The number of hours are classified in two different models; the Weinberger model (number of hours below 45 degrees Fahrenheit (F)); and the modified Weinberger model (number of hours between 32F and 45F).
The values recorded (Weinberger model) as of Feb. 10 include:
Attapulgus 620 (2021-22) 626 (2020-21) 429 (2019-20) 571 (2018-19)
Butler 750 (2021-22) 825 (2020-21) 711 (2019-20) 781 (2018-19)
Byron 835 (2021-22) 867 (2020-21) 783 (2019-20) 817 (2018-19)
Fort Valley 813 (2021-22) 855 (2020-21) 787 (2019-20) 832 (2018-19)
The values recorded (Modified Weinberger model) as of Feb. 10 include:
Attapulgus 573 (2021-22) 539 (2020-21) 439 (2019-20) 529 (2018-19)
Butler 673 (2021-22) 725 (2020-21) 649 (2019-20) 704 (2018-19)
Byron 728 (2021-22) 716 (2020-21) 714 (2019-20) 719 (2018-19)
Fort Valley 724 (2021-22) 702 (2020-21) 719 (2019-20) 705 (2018-19)
Chill Portions
It is a similar outlook for the Dynamic Model which utilizes chill portions, a model better suited for Georgia’s temperature variations accounting for gain and loss of chill.
Chill portions recorded at each site include:
Attapulgus 42 (2021-22) 40 (2020-21) 33 (2019-20)
Butler 52 (2021-22) 50 (2020-21) 48 (2019-20)
Byron 49 (2021-22) 44 (2020-21) 47 (2019-20)
Fort Valley 52 (2021-22) 49 (2020-21) 50 (2019-20)
To have a potentially good crop – at the minimum – by Feb. 15, varieties require
- 650 chill hours need ~ 30-35 Chill portions
- 750 chill hours need ~ 35-40 Chill portions
- 800 chill hours need ~ 40-45 Chill portions
- 850 chill hours need ~ 45-50 Chill portions
- 950 chill hours need ~ 50-55 Chill portions
Chill portion data accumulation from last year compared to this year is similar. Bloom came on normally with an overall good fruit set the last two seasons. Some higher chill varieties had an extended bloom season which created some issues. Growers can expect similar situations this year with some lack of chill symptoms, like delayed bloom and extended bloom, present in some of the higher chill varieties.
The National Oceanic Atmospheric Administration forecast shows 50% probability for above average temperatures for the rest of February. This outlook means that peach trees have accumulated as much chill as they are going to get at this point in the season.
Peaches need chill hours to mature. The required chill hours depend on the specific variety.