460 FUNDAMENTALS OF FRUIT PRODUCTION 



bring their fruits to maturity. Indeed, some question may be raised 

 as to whether the very weak spurs, those that annually push out only 

 two or three small leaves and rarely or never form fruit buds, are of any 

 real benefit to the tree. They draw on the supply of moisture and 

 nutrients obtained from the soil and they can yield but little elaborated 

 food in return. Furthermore, observation indicates that forcing such 

 spurs into vigorous growth, once they become weakened, is extremely 

 difficult. Heavy pruning, alone or combined with certain cultural 

 treatments, may force them to grow out into new shoots and later these 

 shoots may give rise to fruit spurs; however, to reinvigorate them and 

 make them form fruit buds without an intervening shoot growth is 

 very difficult after they have ceased to function satisfactorily for several 

 years. Therefore keeping fruit spurs in a vigorous condition from the 

 start is doubly desirable. 



The vigor and growth of individual spurs depends on (1) the supply 

 of moisture and nutrients from the roots and (2) the supply of elaborated 

 foods stored more or less locally. This locally stored supply in turn 

 depends largely on manufacture at or very near the point in question. 

 Both of these factors are influenced by many cultural practices. Pruning 

 may be a means of modifying, at least temporarily, the supply of moisture 

 and nutrients available for the spurs that are left, through diverting 

 to them large amounts before intake is correspondingly reduced. This 

 effect of pruning can be obtained more readily by fertilizing, tillage, 

 irrigation, mulching or other soil treatments. It may be pointed out, 

 however, that though the effects attending these other cultural opera- 

 tions and those attending pruning are quite similar, in the one instance 

 there is a general influence on the vegetative activities of the tree while 

 pruning has a more specific influence on certain of its parts or local 

 regions. 



Pruning is a more important means of influencing the accumulation 

 of elaborated foods, through admitting more or less light to the spurs. 

 As has been pointed out, the general effect of heading back is to thicken 

 the top, cause more shading and thus probably decreased carbohydrate 

 manufacture in the lower and interior parts of the tree. On the other 

 hand thinning out tends to have the opposite effect. Since the removal 

 of spurs by thinning (either the removal of individual spurs or small 

 spur-bearing branches) has as great a concentrating effect on nutrients 

 as an equivalent heading back, it is to be regarded as the most important 

 pruning practice in this respect. Indeed it is about the only pruning 

 practice that always tends to increase longevity and regularity of bearing 

 in fruit spurs. Consequently the heading back that is done in bearing 

 apple and pear trees should be hmited to that required to keep the tree 

 from becoming too tall and too spreading for the mechanical support 

 of its crop and for convenience in various orchard operations. In 



