Data from today’s Winchester MaluSim simulation (pdf) shows that apple trees have been in a mild carbohydrate deficit for the last couple of days and will likely continue to be in a mild deficit for three to four days. This means that you should expect average to slightly aggressive thinning response from materials apples during this past week. A more severe carbohydrate deficit is predicted for next week, but this will likely be beyond the 10 mm thinning application for most orchards and cultivars. At the AREC, many cultivars are already at or beyond 15 mm. The three-day rolling average shows less of a deficit over the past few days, but also shows that we are heading into a period of severe carbohydrate deficit next week.

We are unsure how well the MaluSim model predicts responses to ethephon-based materials used for late- or re-thinning at ~20 mm. However, it is something that I am testing this year.

As a reminder, MaluSim is based on an idealized Empire tree and uses weather data from the Winchester AREC. Therefore it may not represent conditions in your orchard or with different cultivars. However, please let me know if you are using this data for making management decisions and how well it is or isn’t working so that we can improve the model for future years.