Apple Thinning Update: 4/30/19

— Written By

Image of an apple bloom

Output from the Carbon Balance Model for four sites in western NC (Apple Wedge, Flat Rock, Sugarloaf, and Moravian Falls) and two sites in North Georgia (Blue Ridge and Ellijay) is below (click figures to enlarge).

If you have access to NEWA, I’d recommend calculating the carbon balance for your own site. Predicted weather data is used in these estimates and the forecast can change throughout the course of a day. If you’d like to run the model on your own, the link at the NEWA site is on the drop-down menu under “Crop Management”. Choose a site nearest your orchard location and enter your Green Tip and Full Bloom date. Then hit the green Calculate button.

Based on this output and use of “normal” thinning materials and rates:

  • North Carolina sites: Thinning responses are predicted to be normal to slightly aggressive. Most NC growers are in the middle of a good thinning window if the weather forecast is correct.
  • Georgia sites: Thinning responses are predicted to be aggressive and/or excessive. This is due to the combination of forecasted warm temperatures and cloudy weather over the next few days. Please use caution!

4.30.19: Edneyville (Apple Wedge) Carbon Balance Model Estimates

Date Max Temp Min Temp Solar Rad Tree Carbohydrate Status (g/day) Thinning Rec.
(°F) (°F) (MJ/m2) Production Demand Balance 4-Day Bal.
30-Apr 82 54 18.2 73.92 86.5 -12.58 -15.31 Apply standard chemical thinner rate
1-May 82 60 22.8 82.82 94.92 -12.1 -15.45 Apply standard chemical thinner rate
2-May 81 61 21.4 79.89 93.89 -13.99 -12.05 Apply standard chemical thinner rate
3-May 80 59 16.1 66.26 88.82 -22.56 -6.88 Apply standard chemical thinner rate
4-May 76 58 16.3 71.45 84.6 -13.15
5-May 76 56 19.8 85.93 84.42 1.51
6-May 77 58 24.3 97.61 90.91 6.7

4.30.19: Flat Rock (Richmond) Carbon Balance Model Estimates

Date Max Temp Min Temp Solar Rad Tree Carbohydrate Status (g/day) Thinning Rec.
(°F) (°F) (MJ/m2) Production Demand Balance 4-Day Bal.
30-Apr 81 52 20.3 81.18 98.6 -17.42 -22.64 Decrease chemical thinner rate by 15%
1-May 81 60 22.9 82.53 107.48 -24.95 -21.5 Decrease chemical thinner rate by 15%
2-May 80 61 21.7 80.69 99.9 -19.21 -14.54 Apply standard chemical thinner rate
3-May 80 59 16.3 66.62 95.6 -28.98 -8.43 Apply standard chemical thinner rate
4-May 76 58 17.3 74.62 87.49 -12.87
5-May 75 56 19.7 85.81 82.92 2.89
6-May 77 58 23.8 95.75 90.51 5.23

4.30.19: Edneyville (Sugarloaf Mtn.) Carbon Balance Model Estimates

Date Max Temp Min Temp Solar Rad Tree Carbohydrate Status (g/day) Thinning Rec.
(°F) (°F) (MJ/m2) Production Demand Balance 4-Day Bal.
30-Apr 81 58 18.2 68.71 120.53 -51.82 -37.14 Decrease chemical thinner rate by 15%
1-May 81 60 23.4 83.07 119.13 -36.06 -28.31 Decrease chemical thinner rate by 15%
2-May 80 61 21.6 80.01 111.71 -31.7 -20.05 Decrease chemical thinner rate by 15%
3-May 78 59 16.4 68.43 97.4 -28.97 -11.07 Apply standard chemical thinner rate
4-May 76 58 17.3 74.72 91.25 -16.53
5-May 76 56 19.6 84.91 87.9 -2.99
6-May 77 58 23.8 95.75 91.56 4.19

4.30.19: Moravian Falls Carbon Balance Model Estimates

Date Max Temp Min Temp Solar Rad Tree Carbohydrate Status (g/day) Thinning Rec.
(°F) (°F) (MJ/m2) Production Demand Balance 4-Day Bal.
30-Apr 83 58 19.6 74.78 128.04 -53.26 -38.87 Decrease chemical thinner rate by 15%
1-May 85 60 24 84.41 123.69 -39.27 -31.88 Decrease chemical thinner rate by 15%
2-May 83 61 21.3 80.09 113.39 -33.29 -24.07 Decrease chemical thinner rate by 15%
3-May 81 60 18.2 74.61 104.27 -29.66 -16.1 Apply standard chemical thinner rate
4-May 79 59 16.1 70.36 95.68 -25.32
5-May 78 57 18.5 82.3 90.33 -8.02
6-May 79 60 23.4 94.82 96.24 -1.42

Blue Ridge Carbon Balance chart image

Blue Ridge Predicted Thinning Index: 4.30.19

Date Days after budbreak Carbon Balance (g/day) Thinning Index
30-Apr 50 -45.7 -55.55
1-May 51 -87.0 -59.28
2-May 52 -34.0 -54.85
3-May 53 -56.9 -48.24
4-May 54 -73.7 -32.84
5-May 55 -14.2
6-May 56 -10.7

Ellijay Carbon Balance Model chart image

Ellijay Predicted Thinning Index: 4.30.19

Date Days after budbreak Carbon Balance (g/day) Thinning Index
30-Apr 50 -48.4 -58.3
1-May 51 -91.4 -60.2
2-May 52 -35.1 -59.6
3-May 53 -54.1 -53.7
4-May 54 -89.7 -39.8
5-May 55 -17.2
6-May 56 -12.6

Balanace model recommendations chart image

Notes on Using Output from the Carbon Balance Model

The Apple Carbohydrate Balance Model is a useful tool in making chemical thinning decisions. This model was not developed to account for all factors that influence the efficacy of a thinner application; it was developed to estimate the carbohydrate status of the tree. In short, the carbohydrate balance model is a valuable tool, but other factors need to be considered when making a chemical thinning decision.

A positive carbohydrate balance makes it more difficult to thin whereas increasing carbohydrate deficits are predicted to increase the response to chemical thinning sprays. For example, you might respond to a predicted carbohydrate surplus or mild deficit by either adopting a more aggressive approach to chemical thinning or by waiting until more ideal conditions for thinning develop. Alternatively, if the model is predicting a severe carbohydrate deficit then you might consider reducing the rate of chemical thinner or perhaps not applying a thinner at that time for risk of over-thinning.