Late Thinning Application-May 13, 2019

The average fruit size for Pink Lady, Gala, Fuji and Honeycrisp in Winchester is 16.67, 17.02, 16.3 and 16 mm, respectively. At such advanced stage of apple fruit development, 6-BA and NAA will not be effective as chemical thinners and it is the time to start the “rescue thinning” sprays if more thinning work is still needed. Ethephon is the only effective thinner at this stage. Ethephon thins more effectively when the temperature is in the 70s to low 80s. Although the weather forecast predicts relatively cool temperatures this week, increasing the rate of chemical thinners by 30% to compensate for the high carbohydrate levels, as shown below, might mitigate the negative impact of low temperatures.

The recommended materials and rates for late (rescue) thinning are:

  • Ethephon (1- 1.5 pt) +Sevin (1pt)/100 gallon for Fuji and Spur-type Red Delicious.
  • Ethephon (0.75 pt) +Sevin (1pt)/100 gallon for Gala, Cameo, Goldrush and Jonagold
  • Ethephon (0.4-0.5pt) +Sevin (1pt)/100 gallon for Golden Delicious, Rome Beauty and Enterprise.

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