Flower and Fruit Thinning 237 



branches (Murneek, 1950; Batjer and Uota, 1951). There are varietal 

 differences in sensitivity as well: such varieties as Jonathan respond 

 well to as little as 5 to 7 nig. /I. sodium naphthaleneacetate and 

 Golden Delicious ajjples respond well to 20 to .SO mg./l. Peaches 

 respond only to higher concentrations of 40 to 60 mg./l. and olives to 

 100 to 125 mg./l. Spraying of apple trees from airplanes is done with 

 much more concentrated preparations, usually 2400 mg./l. of the salt 

 in a 40% oil emulsion (Batjer and Thompson, 1948). 



The timing of auxin thinning sprays is much less crucial than the 

 timing of caustic thinning sprays. Caustic sprays may be applied 

 effectively only during the blossom period and after some fruit-set 

 has occurred, whereas auxin sprays may be effective for four weeks 



70- 



50 



Q- 

 O 



o 





UJ 

 O 



q: 



UJ 

 Q_ 



30 



10 



20 



30 



40 DAYS 



TIME OF APPLICATION 



Fig. 101. The effect of time of application after full bloom upon the efficiency 

 of thinning sprays of auxin (naphthaleneacetic acid) applied to peaches (data of 

 Hibbard and Murneek, 1950). 



