Hi everyone,

I apologize for the delay with this update. I was waiting for the last bit of chill to be seen in our regions. We just got a cold front last weekend and early this week and I thought will wait until we could finally see what we got during that time. Now, our weather looks like is going to stay warm, which means probably we are done with chill accumulation.

As in previous years, first let’s start with the traditional chill models:

1) The Weinberger Model (# hours below 45F) and

2) The Modified Weinberger Model (# hours between  32F and 45F). Data is from Oct 1 to Feb 10.

Here are the values by Feb. 10, 2023

Chilling Hours Under 45 ℉ (Weinberger model)
Station Name2022 TO 20232021 TO 20222020 TO 20212019 TO 20202018 TO 2019
Fort Valley676813855787832

Chilling Hours Between 32 ℉ and 45 ℉ (Modified Weinberger model)
Station Name2022 TO 20232021 TO 20222020 TO 20212019 TO 20202018 TO 2019
Fort Valley542724702719705

We did accumulate some additional chill as previously mentioned. We have a nice summary across Georgia as of now for all stations at UGA in: http://weather.uga.edu/?content=ch. Overall we accumulated an additional 80-100 chill hours across locations since Feb.10 to Feb. 22.

This season we stayed on track to match last year’s chill accumulation for a while until about the end of January, but then suddenly our chill was gone. We are about 100 to 140 chill hours below last season. Last year, we saw issues with high chill requirement peaches and some delayed/extended bloom. This year, we have less chill accumulated. One comment that I think is important to keep in mind is that we have not had really warm sunny periods of weather where sun has been shinning on the trees – temperatures in the trees can get really high on those conditions. Overall our days have been over casted and with rain – which although is not accounted in any chill model, I think it does make a difference.

3) The Dynamic Model

So, how about the dynamic model situation? The dynamic model as you all know is better suited for our temperature variations accounting for gain and losses of chill. Currently, we cannot obtain a comparison year after year, but I have been keeping records of last few years.

The site that I am using for obtaining the data for chill portions is https://climatetoolbox.org/tool/historical-climate-dashboard.

You will need to add your location. So, click on choose location. Next, you can choose your data option. There are four panels. You need to add in two of those panels the chill calculation options. Click on the drop down menu and you will be able to see an option for the Modified Weinberger model and one for chill portion (Dynamic model). The nice thing about this tool is that you don not have to look for station IDs. Climatetoolbox is based on NWS (NOAA National Weather Service data). Again, I need to state what Dr. Knox (UGA Agricultural Climatologist) has mentioned before: “the data source for the calculator appeared to be a grid based on NWS data supplemented with some other networks (but not the UGA network) and I believe it should be a reasonable source of data. Keep in mind that there are going to be some variations in local microclimate at your sites due to slope, soil type, and other factors which may make the values different than what the grid is predicting, but it’s the only place I know that you can find a chill portion calculator now”.

Chilling portions (Dynamic model)
Location2022 TO 20232021 TO 20222020 TO 20212019 TO 20202018 TO 20192017 TO 20182016 TO 2017
Fort Valley46524950

So, for chill portion data accumulation we are about 2 to 6 chill portion units from last year for the middle GA area. In the case of chill portion, we use the following correspondence table with chill requirement (adapted from Dr. Reighard)

To have a potentially good crop – at the minimum – by Feb 15th varieties requiring

  • 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

Currently, we are in 46 chill portions in middle GA. We are just below what we were last two seasons. We are quite similar to 2019 to 2020 season. Based on my notes, the 2019 to 2022 season was characterized by prolonged bloom in high chill cultivars. At this point, we are probably going to see issues with specific variety(ies) that have been presenting issues last seasons (high chill), with either delayed or extended bloom. We probably have gotten all the chill that we were going to receive for this season. In my notes also have that overall the crop was good in the region and we hope for a similar situation.

Please if you have any questions, comments, and suggestions, or if you would like to have a conversation about our current situation please feel free to contact me at 352-871-3981 or dchavez@uga.edu.

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