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Apple Thinning in 2012 – Postponed, not Cancelled!

Posted: April 17, 2012

Several cold temperature events before and during bloom occurred in 2012. This resulted in apple flower mortality, and there is also a possibility of some non-lethal injury to flowers and/or spur leaves. This leads to some uncertainty about the number and strength of initial fruit set.
Using the Equilifruit Disk: A round plastic disk with various size notches on the outside. The notches that are presnet correspond with 3 pieces of information: 1. The branch diameter 2. A fruit number 3. A delta value

Using the Equilifruit Disk: A round plastic disk with various size notches on the outside. The notches that are presnet correspond with 3 pieces of information: 1. The branch diameter 2. A fruit number 3. A delta value

 

Dr. Jim Schupp, Penn State Fruit Research and Extension Center Pomologist

For many apple orchards in our region, the level of uncertainty about set suggests that this is not a year to apply thinners at petal fall. In 2012 it may be better to postpone thinning until fruit diameter reaches 10 to12 mm, and use this interval of time to do a more thorough assessment of initial set and fruit growth. A block-by-block evaluation of initial set, seed numbers, followed by the measurement of fruit diameter every two to three days is advised. Growers who have an Equilifruit disk can also use this as a tool to evaluate initial set on a number of limbs in each block to get a better understanding of the need for thinning. For example, if a given size of limb has a capacity (F value) of 12 fruits, and there are 36 fruits that appear to be set, then there are three times as many fruits as needed. If several limbs of the same variety in the same block produce a similar outcome, then chemical thinning would be advisable. While it is still too early to determine initial set in many blocks, those that are at petal fall appear to have more than adequate fruit numbers, and will probably need to be thinned. If these fruits continue to grow, then chemical thinning will be required. Remember: growing fruit are setting fruit!

 

To obtain an Equilifruit disk for assessing apple crop load, contact Tara Baugher at tab36@psu.edu.

 

Contact Information

James Schupp
  • Professor of Pomology
Email:
Phone: 717-677-6116