Flower and Fruit Thinning 239 



from apples (Southwick and Weeks, 1950). Similarly, it has been found 

 that olives can be thinned with auxins only until natural drop has 

 stopped, and after that auxin sprays have no thinning effect (Hart- 

 mann, 1952). It is known that "June drop" of apples is associated 

 with a low production of auxin (Luckwill, 1953), after which auxin 

 production in the young fruit is relatively high (see figure 103). 



Many workers have noted that auxin applications selectively thin 

 the fruits on weak or small spurs preferentially. In fact, even on large, 

 vigorous spurs the peripheral fruits are more susceptible to thinning, 

 and the center or "king" fruits are the most tenaciously held (Batjer 

 and Thompson, 1948). 



The fruit thinning action of auxin sprays brings about an in- 



O 



oc 



\- 

 z 

 o 

 o 



u. 

 o 



UJ 



o 



UJ 

 Q. 



Average 

 fruit weight 

 at harvest 



10 



20 



30 DAYS 



TIME OF AUXIN APPLICATION 



Fig. 102. The differences in fruit weight and in per cent of fruits set on Craw- 

 ley Beauty apples obtained with various times of application after petal-fall of a 

 fruit thinning spray (20 mg./l. naphthaleneacetic acid) (Luckwill, 1953). 



