What is apple fruit thinning?

Apple fruit thinning involves removal of flowers and immature fruits early in the spring so that it can help in improved fruit size at harvest. Fruit thinning can be done either by hand or by spraying chemical to the tree. The main advantage of hand thinning is that poor quality or damaged fruit can be removed. Initially, apple fruit thinning was done by hand, but this practice is no longer in use. Hand thinning is very labor intensive and can not be done in commercial orchards. Chemical thinning is easy to done by spraying the chemicals directly to the apple trees.


What are the advantages of apple fruit thinning?

Apple fruit thinning is very important to the success of apple industry because in “on” year heavy cropping results in no or low cropping in the “off” year. Thus apple fruit thinning reduces alternate bearing of fruit.

The main advantages of fruit thinning are—

  • It improves fruit size and quality,
  • It helps in return bloom,
  • It reduces the chances of breaking the branches,
  • It helps in penetrating the sunlight to the branches,
  • It avoids the risk of alternate bearing,
  • It may suppress the spreading of pests.

Apple fruit thinning increases leaf to fruit ratio. Apple varieties require leaf to fruit ratios between 40:1 and 75:1 (40 to 75 leaves per fruit) to reach appropriate size at harvest. However spur varieties need smaller fruit to leaf ratio to attain good crop size.


Chemical thinning by NAA (1-napthaleneacetic acid) (Planofix)

NAA is a chemical thinner that has a potential to thin whole clusters when sprayed at higher concentration. It is used at rates between 10 and 20 ppm. It is active compound; there may be a chance of over thinning when there are high temperatures. It can also reduce fruit size if applied at higher concentrations or too late after petal fall. NAA can be applied between petal fall and 17mm fruit diameter. The optimal response to NAA is when fruits are between 10 to 12 mm in diameter. The appropriate dose of NAA is 45 ml/200 liters of water. Treat NAA with care, especially when high temperatures prevail!


Factors affecting Thinning

The main factors affecting thinning are:

  • Thinning process is low in sunny weather.
  • Thinning process is easy when there are heavy clouds.
  • Thinning is less in cool weather below 18 degree Celsius.
  • Thinning is more in hot weather above 28 degree Celsius.
  • Thinning process takes best in temperature range between 21 and 27 degree Celsius.
  • Thinning process depends upon variety to be thinned. Some cultivars are easy whereas some are harder to thin. Cultivars such as “GOLDEN DELICIOUS” are harder to thin.
  • Trees in low vigor may be easily thinned.
  • Trees are easier to thin if rain occurs before or after spray application.
  • Trees are easier to thin if moisture and nitrogen supply is inadequate or any other stress which affects tree performance.

Mode of action of Apple Thinning Chemicals

  • Abortion of seeds or inhibition of seed development
  • Nutrient transport inhibition to the fruit
  • Decrease in process of photosynthesis


  • Use the suggested rates of chemicals, over dosage can result in over thinning or pygmy fruit.
  • Leave several non sprayed trees so that you can check the results of using thinners.
  • Use extra precaution if there are freezing temperatures during bloom.
  • Late post bloom sprays of NAA can result in mummies and pygmy fruit.



NAA can completely thin the fruits resulting in no crop. Use NAA at your own risk. does not take any responsibility for any adverse effects caused by spraying NAA.










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