In 1991, mature, vigorous Gardiner Deli- 

 cious/MM.106 trees were treated with 500 ppm 

 ethephon eight days after petal fall, and in 1992, 

 mature, vigorous Rogers Red Mcintosh/ 

 MM. 106 trees were treated with 500 ppm ethe- 

 phon four days after petal fall. During the 

 season of treatment, we assessed fruit set, veg- 

 etative growth, frxdt ripening, fruit drop, and 

 fruit size. 



Use of ethephon soon after bloom, as was 

 done in this study, has been shown to thin fruit, 

 and in fact, ethephon is used as a chemical 

 thinner in some locations around the world. In 

 this experiment, however, the ethephon treat- 

 ment did not thin significantly and had very 



little effect on fruit set. We all know that 

 chemical thinners do not work every year, and 

 they do not work under all circumstances. The 

 lack of a thinning response from ethephon in 

 this study should not be taken to mean that 

 ethephon will not thin fruit under our condi- 

 tions. From a practical standpoint, if ethephon 

 is to be used as a growth retardant, the grower 

 must be prepared for a potential reduction in 

 fruit set, even if it Likely will not occur in all 

 circimistances. 



Research by others has shown that ethep- 

 hon has only a moderate effect at best on termi- 

 nal growth reduction. The most noticeable 

 growth reduction comes from preventing spurs 



fruit Notes, Fall, 1993 



11 



