Carbohydrate Model Run: Thinning Time is Here!

Posted: May 14, 2018

It looks like spring finally arrived in the last two weeks and many orchards are thinning apples.

Growers should be checking the carbohydrate model on a daily basis to have an idea of how trees might be responding to chemical thinner applications. As mentioned at a number of the twilight meetings in the last couple of weeks this year bloom is later than it has been in some years. Due to the later bloom, there is a greater chance that temperatures during thinner applications may be more favorable to inducing fruit drop. In particular temperatures in the 70’s will improve response to applications of 6-BA and NAA.

This is the first Carbohydrate Model run for multiple orchard sites. There are three sites in Adams County and single sites in all the other counties. Currently, we are reporting for seven counties and ten orchard sites. Full bloom has yet to be reported in the northern sites in Erie and Lackawanna counties.

Apple Carbohydrate Thinning Model Data

To properly use the model choose the orchard closest to your geographic location select the “continue” button and check to make sure your green tip date and full bloom date are entered if it is different from yours. Hit the green “Calculate” button once your dates are entered.

Please note that the model is updated in real time. The current day uses available data and then fills out the rest of the day with the forecast data. As the day goes on, there will be more and more observed data and less and less forecast data. Therefore, if weather conditions change from the forecasted data the results may change.

The tables are arranged by county, and the weather station from which the model was run is listed above the table, along with green tip and full bloom dates for that location. The row that is highlighted in bold is the date the model was run.

The sites are predicting temperatures in the 70–80-degree range through Thursday. All sites showed low sunlight levels yesterday but mostly sunny days the rest of the week. Remember that high temperatures may result in increased thinning, but you also need to consider the fruit size and your local light conditions. All the sites outside of Adams County suggest a decrease in chemical thinner rate by 50%.

Contact Information

Robert Crassweller
  • Professor of Horticulture
Phone: 814-863-6163