Effects of root pruning and benzyladenine application on tree growth and fruit size in 'Empire' and 'McIntosh' apple

In three trials over three years, postbloom applications of benzyladenine (BA) thinned young fruitlets of both “Empire” and “McIntosh” apples trees, increased fruit weight, and reduced yield per tree. Increases in shoot growth and/or trunk enlargement were observed in BA-treated trees in some of the trials. Root pruning consistently reduced shoot growth and /or trunk enlargement in all trials reported here. In most of the trails, root pruning reduced fruit load rather than fruit size. The absence of an increase in fruit size under reduced fruit-load conditions is consistent with a negative effect of root pruning on fruit size. BA consistently increased fruit size and improved fruit-size gradeout in 1991. Return bloom was promoted in some of the trials by BA and in al but one trial by root pruning. Effects of BA and root pruning largely were independent. These results suggest that BA can be used to improve fruit size in root-pruned apple trees, but only at the expense of a reduction in yield. Chemical name...