440 



FUNDAMENTALS OF FRUIT PRODUCTION 



in effect parasitic and it is not until they have been active for some time 

 that they have fully replaced the materials used in their growth. Sum- 

 mer pruning removes them after they have levied their tax on the 

 tree's reserve foods and often before they have contributed much to its 

 welfare. It must have, generally, a greater retarding influence on net 

 increase in size than a correspondingly heavy winter pruning. This 

 devitalizing effect of summer pruning has been noted by many observers 

 and recently has been the subject of a number of experimental studies. 

 Alderman and Auchter^ found that young summer pruned apple trees 

 averaged only 120 feet of new shoot growth in 1915 while winter pruned 

 trees of the same age and of the same varieties averaged 188 to 216, 

 according to the severity of the pruning. The summer pruned trees 

 increased in spread, height and circumference more rapidly than trees 

 pruned very severely in the winter, but much less rapidly than those 

 pruned moderately or lightly in the winter. Apple trees just coming into 

 bearing produced, after winter pruning, shoots that were 20 to 50 per 

 cent longer and 10 to 20 per cent thicker than those on summer pruned 

 trees. In one orchard under investigation they found that the total leaf 

 area of summer pruned trees averaged only from 299 to 459 square feet, 

 that of trees pruned both summer and winter averaged from 527 to 794 

 square feet and that of trees pruned only during the winter averaged 

 from 660 to 1144 square feet. Not only were there fewer leaves on the 

 summer pruned trees, but these leaves averaged smaller in size. The 

 leaves of the summer pruned trees were paler and yellowish, suggesting 

 an additional reduction in their photosynthetic abilities. Arkansas and 

 York Imperial trees in full bearing, on the other hand, showed practically 

 no difference in the responses to summer and to winter pruning. In 

 fact the summer pruned trees of middle age produced more terminal 

 shoot growth than those pruned lightly during the dormant season, 

 though somewhat less than those pruned heavily. Table 13 presents 

 data obtained in England from pruning back weak declining plum trees at 

 various seasons. The figures show the relative lengths of the new 

 shoot growth. In this case the July pruning was little short of disastrous 

 to the trees. Certain experimental results obtained in Virginia from 

 various summer and winter prunings combined with special practices 



Table 13. — Relative Length of New Shoots of the Plum, Cut Back at 

 Different Dates 

 {After Bedford and Pickering'^) 



