CHEMICAL FRUIT THINNING OF APPLES

Chemical fruit thinning is an established practice in all apple producing areas of the world. The immediate objective of thinning is an increase in fruit size because an excessive crop always results in a high percentage of small fruits. An excessive crop may also adversely affect fruit color, sugars and other flavor components, and fruit condition and storage life. These negative effects of an excessive crop are due to an unsatisfactory leaf/fruit ratio. The leaves, through the process of photosynthesis, produce all the carbohydrates that are used in fruit growth and that contribute to fruit quality. Optimum fruit size and quality require about 30 leaves/fruit. Fruit thinning improves the leaf/fruit ratio by increasing the leaf area available to each of the persisting fruits. Obviously, the number of leaves cannot be increased; therefore, adjustments in the leaf/fruit ratio are possible only by reducing the number of fruits. Effective f ruit thinning is usually rewarded handsomely. This point is well illustrated by data col