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Apple Carbohydrate Thinning Model

The Cornell Apple Carbohydrate Thinning Model is an attempt to factor in the interaction of environmental conditions and a tree’s physiological status for precision crop load management.

Weather conditions affect an apple tree’s response to chemical thinners.  The model utilizes temperature, solar radiation and day length based upon site-specific ground based measurements from a weather station in a grower's orchard block.

To adapt models for your own orchard:

  1. On the Cornell NEWA website, go to Apple Carbohydrate Thinning (found on their drop-down menu under Crop Management)
  2. Click on the leaf on the map closest to your site
  3. Click continue
  4. Enter your Green Tip Date and Full Bloom Date then hit the green Calculate button

Special Notes for Tables

  1. The 4 Day Average Balance values are derived from the current day Balance and the next 3 days to account for how the trees may respond based on predicted weather.
  2. The model is only as good as the predicted weather forecast. If the weather changes dramatically from the forecast recheck the model.
  3. Bud break and bloom dates are from grower evaluations of their orchards.

Table 1. Decision rules for using the output of the Carbohydrate model to adjust chemical thinning rate

4-day Av. Carb. BalanceThinning RecommendationLevel Rating
> 0g/day Increase Chemical Thinner Rate by 30% None
0g/day to -20g/day Apply Standard Chemical Thinner Rate Normal
-20g/day to -40g/day Decrease Chemical Thinner Rate by 15% Low deficit
-40g/day to -60 g/day Decrease Chemical Thinner Rate by 30% Moderate deficit
-60g/day to -80 g/day Decrease Chemical Thinner Rate by 50% High deficit
< than -80g/day Do not thin (many fruits will fall off naturally) Very high deficit

Apple Carbohydrate Thinning Models for Pennsylvania Counties

Cornell Carbohydrate Model Run for May 30, 2017

This is the last run of the season. I suspect that fruit size is or soon will be too large to provide adequate response to thinner application.

However, if you need a rescue treatment for underperforming previous applications, please refer to the section in the current Tree Fruit Production Guide titled “Late Thinning” (bottom of page 66 and continued onto page 67 in your paper copy). There is a discussion for late thinning depending upon how much fruit you need to remove.

Most of the sites are now beyond 25 days after full bloom or will be so by the end of the week. If you look at the model you will note that there is no longer a recommendation for chemical thinner adjustment although the model will continue to run the numbers. If you need to know what the model recommends look in the “More Info” tab and select “Model overview.” The table at the bottom of that page will provide the appropriate recommendation for the 4 day average balance.

This year’s weather has certainly been challenging. In addition to the charts for the past week I created two season long charts for Biglerville and Rock Springs. You will notice that in general the two sites had similar trends rising and falling in unison. However, the peaks and valleys for Rock Springs never hit the highs and lows that occurred in Biglerville. We also had cold damage on the mornings of May 8 and May 9 that resulted in damage to the young fruitlets. After looking at the fruit the afternoon of May 8, I thought we would not have any fruit. As it looks now we have fruit albeit some frost rings as well as cracked fruit that look like they will stay on.

Apple Carbohydrate Thinning Model for Biglerville, Piney Mtn, and York Springs.

Apple Carbohydrate Thinning Model for Pittsburgh Airport.

Apple Carbohydrate Thinning Model for Bedford County

Apple Carbohydrate Thinning Model for the Reading Airport.

Apple Carbohydrate Thinning Model for Cabot, Butler County

Apple Carbohydrate Thinning Model for Rock Springs.

Apple Carbohydrate Thinning Model for Escarpment

Apple Carbohydrate Thinning Model for Scott Township.

Apple Carbohydrate Thinning Model for Hegins.