Carbohydrate Model Results for May 15, 2017

Over the weekend most sites showed a positive balance of carbohydrates, meaning trees were less responsive to applications of chemical thinners.
Carbohydrate Model Results for May 15, 2017 - News

Updated: April 12, 2018

Carbohydrate Model Results for May 15, 2017

Photo: R. Crassweller, Penn State

It looks like we will finally experience some warmer temperatures this week, especially on Wednesday and Thursday. In some locations the highs are expected to be in the low 90s. With those high temperatures predicted it would be a good idea to look at the model again on those days. The temperatures are finally conducive to the use of 6-BA products. In the chart below note that any positive 4-day average carbohydrate balance numbers indicate a need for a stronger thinner rate. Balances between 0 and -20 suggest using the standard rate of thinner that works best for your orchard and varieties.

Apple Carbohydrate Thinning Models for Pennsylvania Counties

For more information on the carbohydrate thinning model, visit Carbohydrate Thinning Model. For more details on factors that affect plant growth regulator performance and chemical thinner rates, visit Growth Regulators in Apple and Pear Production.

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

4-day Av. Carb. Balance Thinning Recommendation Level Rating
> 0g/dayIncrease Chemical Thinner Rate by 30%None
0g/day to -20g/dayApply Standard Chemical Thinner RateNormal
-20g/day to -40g/dayDecrease Chemical Thinner Rate by 15%Low deficit
-40g/day to -60 g/dayDecrease Chemical Thinner Rate by 30%Moderate deficit
-60g/day to -80 g/dayDecrease Chemical Thinner Rate by 50%High deficit
< than -80g/dayDo not thin (many fruits will fall off naturally)Very high deficit


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More by Robert Crassweller, Ph.D.