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VARIABLES INFLUENCING SIZE OF APPLE TREES, AND SUGGESTED TREE SPACINGS 



William J. Lord, Department of Plant and Soil Sciences 



Apple trees on size-controlling rootstocks (compact trees) can produce 

 more bushels of U.S. Extra Fancy grade fruit per acre and reach maximum pro- 

 duction at an earlier age than larger trees because of better exposure of 

 foliage and fruit to light and bearing surface and more bearing surface per 

 acre. Unfortunately, the increase in productive leaf surface and/or early 

 yields frequently are not as great as would be expected because of influen- 

 ces of soil and management (includes supporting leaders) on tree size and 

 tree spacing. 



In this article we list some of the variables that influence tree size 

 and give examples of the effects of these variables based on measurments at 

 the Horticulture Research Center and grower orchards, and observations in 

 pruning trials (Table 1). These illustrations show why it is extremely dif- 

 ficult to select the correct tree spacing. 



We have learned that, under our conditions, very close tree spacings 

 generally are not satisfactory in Massachusetts because of tree crowding 

 problems. In contrast, trees in many plantings on M26 have failed to fill 

 their allotted space, and leaf surface per acre is further reduced because 

 of the failure to support the leaders. The writer recognizes that it is not 

 possible to select perfect tree spacings because of the variables influenc- 

 ing tree size. Nevertheless, the guide in Table 2 may prove useful since it 

 represents our experience over many years. 



We have allotted an 8 foot alley for orchard travel, with some excep- 

 tions for trees on M9 rootstock. Reducing the between-row spacing by 2 feet 

 will increase tree number considerably but unless smaller equipment is 

 available a 6 foot alley may be too restrictive for orchard operations. 



"Mark", a recently released rootstock will create considerable commer- 

 cial interest. Our very limited data indicate that Mark may produce a tree 

 slightly larger than M26. For trees on Mark we tentatively suggest allowing 

 2 feet more spacing in the row and between rows than suggested for trees in 

 Table 2 on M26, M9/111 or M^/infi. 



