-7- 



WIL\T IS A SEMI-WARF APPLE TREE? 



The answer to this question is not so simple as it first appears. To some 

 people it may mean a tree propagated on any of the East Mailing rootstocks, to 

 others it may mean a tree propagated on a specific stock such as East Mailing VII, 

 while there are still others who think of a semi-dwarf tree as one which has an 

 interstock of one of the East Mailing rootstocks. One can readily see that tree 

 performance can not be the same for the three catagories and that a state of 

 confusion exists in regard to terminology with respect to semi-dwarf trees. 



In order to have an idea as to what constitutes a semi-dwarf tree, one must 

 first have an understanding of the East Mailing rootstocks. This series of East 

 Mailing rootstocks, usually shortened to "EM rootstocks," is identified by Roman 

 numerals rather than by name. These stocks differ from seedling stocks in that 

 they are propagated by layering or cuttings rather than from seeds. EM stocks 

 are clones or rootstock varieties and each stock originated from a single indi- 

 vidual the same as the Mcintosh variety originated from a single individual. 

 The degree of tree vigor which EM stocks will produce depends on which numbered 

 stock we choose; it ranges all the way from very dwarf, semi-dwarf, vigorous to 

 very vigorous. For example, EM IX produces a very dwarf tree; VII a semi-dwarf 

 tree; XIII a vigorous tree and XII a very vigorous tree. The degree of dwarfing 

 which a given rootstock will produce also depends on the variety which is prop- 

 agated on it. Vigorous varieties will not have their growth restricted so much 

 by a semi-dwarfing stock as will weak varieties. A weak growing variety may have 

 its growth restricted too much by EM VII while a vigorous variety may have its 

 growth controlled to the desired size. 



Another method of controlling tree size is by the use of an interstock of 

 one of the EM very dwarfing stocks such as EM VIII or IX. This method consists 

 of inserting a short stem piece of EM VIII or IX between the seedling rootstock 

 and the scion variety. The degree of dwarfing obtained by this method depends 

 upon the length of the stem piece and EM stock used for the stem piece. Trees 

 which are produced in this manner will be larger than trees which are budded 

 directly to the rootstock used as the stem piece. For example, if EM VIII is 

 used as an interstock the trees will be somewhat larger than trees which are 

 grown directly on EM VIII roots; similarly, if EM VII or II is used as the 

 interstock the trees will be larger than trees on EM VII or II roots. In other 

 words, trees produced by the interstock method are not identical with trees grown 

 directly on a given EM stock. 



In light of this discussion it should be apparent that the terms dwarf and 

 semi-dwarf have very little meaning, unless the variety, rootstock and method of 

 propagation are stated. The following method of designation, such as Mcintosh/ 

 EM VII, and Mclntosh/EM IX/domestic seedling root, is suggested as a means of avoid- 

 ing the confusion regarding dwarf and semi-dwarf trees. McIntosh/EM VII signifies 

 a Mcintosh scion on an East Mailing VII rootstock, while Mclntosh/EM IX/domestic 

 seedling indicates a tree which comprises a Mcintosh scion with an intermediate 

 stem piece of East Mailing IX on a domestic seedling root. If nurseryraen would 

 adopt this method of designation in their catalogue listings and fruit growers 

 would place their tree orders on this basis, then the grower would be more likely 

 to get the kind of tree he wants. 



W. D. Weeks 



I I I I I I I I I I I I I I I I 



