approximately 60°F with little wind, and by mid 

 afternoon, the temperature had risen to the lower 70 's. 

 Initial set was determined by counting all persisting 

 fruit on tagged limbs at the normal time for hand 

 thinning, about 45 days after bloom, when fruit 

 diameter averaged 1 inch. Hand thinning was done to 

 a commercially acceptable level on each tagged limb, 

 by spacing fruit to about 6 inches apart. The number of 

 fruit hand thinned from each limb was counted and 

 recorded. Initial fruit set, hand thinned fruit, and final 

 set were calculated based upon the cross-sectional area 

 of each limb. Ten fruit or the number of fruit ready for 

 commercial harvest were sampled from the tagged 

 limbs on July 23, 27, and 30 for Garnet Beauty, and on 

 August 5, 10, and 12 for Redhaven. Harvested fruit 

 were taken to the laboratory where they were weighed, 

 the average fruit weight calculated, and then the 

 diameter of each fruit measured with a hand-held fruit 

 sizer. 



Results 



Blossom thinning treatments significantly re- 

 duced initial set and the number of fruit that needed to 

 be removed by hand thinning (Table 1). ATS appeared 



to reduce initial set the most, although the 6-gallons- 

 per-acre rate was the only one to reduce initial set and 

 final set below that of endothall and Wilthin. Fruit 

 weight and fruit diameter at harvest were increased by 

 all blossom thinners. ATS increased fruit weight and 

 diameter most dramatically, endothall was intermedi- 

 ate, while Wilthin had the smallest effect. The lowers 

 rate of Wilthin, 6 quarts per acre, did not increase fruit 

 weight or diameter relative to the control. 



Discussion 



One of the goals of this investigation was to 

 identify concentrations of thinning chemicals that 

 would consistently and effectively thin peaches. ATS 

 caused excessive thinning, phytotoxicity, and shoot 

 dyeback in 1997. Part of the response was due to the 

 higher rate used than reported in other investigations. 

 Another component was that the amount of spray 

 deposited was increased in portions of the tree when 

 the sprayer application was into the wind estimated to 

 be 25 mph. Rates were lowered in 1998 and 

 applications were made under favorable thinning 

 conditions. Insufficient thinning was achieved at the 

 low rate. Concentrations were again adjusted in 1999 



Fruit Notes, Volume 64 (Number 4), Fall. 1999 



