Light, a Key Factor in Efficient Apple 

 Production 



James T. Williams 



Cooperative Extension, University of Massachusetts 



Light interception in the orchard and its distri- 

 bution throughout the tree canopy affects flower bud 

 formation, fruit set, fruit development, and fruit 

 quality. Orchardists can use pruning and tree 

 training to maximize the light interception of the 

 orchard, and therefore the orchard efficiency. This 

 article will review light as it relates to maximizing 

 fruit production and quality. Much of the informa- 

 tion for this article is from: Rom, C. R. and B. H. 

 Barritt. Light interception and utilization in or- 

 chards, pp. 41-59. In A. B. Peterson (ed.). Intensive 

 Orcharding. Goodfruit Grower, Yakima, WA. 



If 100% of the sunlight received by an orchard 

 was absorbed, the ideal situation would exist. 

 However, this situation is impractical, because there 

 must by open spaces to allow equipment operation 

 and harvesting. Research has determined that or- 

 chard production is maximized when 70% or more of 

 the light striking an orchard is utilized. The earlier 

 in the life of the orchard that maximum light utiliza- 

 tion occurs, the quicker maximum production is 

 attained. Therefore, trees must develop leaf surface 

 quickly and over a large portion of the land area to 

 be most efficient. In Washington, well-feathered 

 trees will develop approximately 22 square feet of 

 leaf area in their first year and up to 63 square feet 

 in their second year. This growth will be less in New 

 England due to the reduced available sunlight. 

 Obviously, increased tree density will affect total 

 light utilization in the first few years after planting. 



When one considers the whole tree, fruiting spur 

 leaves make up 15 to 25% of the total canopy leaf 

 area, non-fruiting and vegetative spurs may com- 

 prise 30 to 40% of the leaf area, and the remaining 30 

 to 40% of the leaf area is composed of extension shoot 

 leaves. Approximately a month after spur leaves 

 emerge they are unable to maintain fruit growth at 

 proper rates so the larger leaves emerging from 

 spurs (called bourse shoot leaves) and normal vege- 

 tative shoot leaves supply carbohydrates for fruit 

 growth. Vegetative spur leaves supply carbohy- 



drates to the fruit, but of more importance, assist in 

 flower but formation. These leaves must receive 

 ample light during the time of flower bud formation. 

 Research has shown that only about 15% of the light 

 energy intercepted by a leaf passes through, the rest 

 being either absorbed or reflected. The closer to the 

 center or bottom of the tree, the less light is avail- 

 able. When light travels 3 to 6 feet through the tree 

 canopy, its light energy is reduced to 30% and at that 

 point falls below the threshold that a leaf needs. 

 Therefore, it becomes evident that dense tree cano- 

 pies limit growth and development in almost 1/3 of 

 the canopy volume. In order that fruit quality, 

 flower bud formation, and fruit growth be maxi- 

 mized, 30 to 50% of the full sunlight is necessary so 

 that photosynthesis can function at efficient levels. 

 Only then can wood growth, leaf growth, fruit 

 growth, and fruit sugars be developed fully. Addi- 

 tionally, light is also important for fruit color. The 

 fruit must be hit directly by 50 to 75% available 

 sunlight in order that anthocyanin pigments be 

 developed and skin color maximized. 



It is important that leaves be exposed to maxi- 

 mum sunlight at the beginning of the season, be- 

 cause those leaves that are shaded early in the 

 season and then exposed to full sunlight never attain 

 a rate of photosynthesis equal to those leaves that 

 were exposed to full sun for the entire season. Proper 

 light management is necessary from the beginning 

 of the season to the end. A combination of dormant 

 and summer pruning and a high density training 

 system maximizes the light throughout the tree 

 canopy. 



Trees "remember" the low light intensities re- 

 ceived the previous year by providing fewer flowers, 

 lower fruit set, and smaller fruit. Light manage- 

 ment is a very important operation to improve pro- 

 duction, fruit quality, and repeat crops, and should 

 be regarded as a continuous function in the orchard. 



Next issue will discuss seasonal light require- 

 ments in the orchard. 



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Fruit Notes, Fall, 1990 



