Tree fruit physiologist and developer of the apple carbohydrate thinning model, Alan Lakso, Cornell University, advises caution when using the NEWA apple carbohydrate thinning model:

(1) The apple carbohydrate model assumes that the trees are healthy, with normal vigor, have no significant stress (frost, drought, nutrient) and no significant carry-over effects from previous years that might change the tree response to the weather.  With the severe drought in 2016, there may be orchards that will have a weakened state coming into 2017 which would likely make the tree abnormally sensitive to thinners.  So in those cases the model may suggest a stronger thinner concentration than is appropriate. Conversely, if irrigated last year, with the warm season and lots of sun, those trees may be in better than normal condition and harder to thin.

(2) With the cold spring weather period currently being seen across much of New York and the Northeast, flowering, pollination, initial set and early fruit growth may not be very well modeled because we did not have much data under these very cold (or also excessively hot) conditions when the model was developed.

For all these reasons, you should have less confidence in the model this year.  Use your experience with your unique situation.

Everyone, please pass this on to whomever might be appropriate.  Also please get back to Alan Lakso with your observations of when the model seemed to work or not work this season.  That will be critical to make appropriate adjustments or confirm knowledge of model limitations.

Here is Dr. Lakso’s email contact information:
Alan N. Lakso,  Professor Emeritus
Horticulture Section, School of Integrative Plant Sciences
Cornell University
NY State Agricultural Experiment Station
Geneva, NY 14456
https://hort.cals.cornell.edu/people/alan-lakso
Email anl2@cornell.edu (preferred)

The NEWA region spans from Minnesota to New Hampshire to North Carolina. For some regions this cautionary note may not apply, but it will be important to keep these aspects of the apple carbohydrate thinning model in mind for future years.