Removal of flower buds, flowers or small fruitlets significantly increases peach fruit size at harvest. Due to the lack of labeled or consistent thinning chemicals, peach growers wait ~30 days after full bloom when fruit set is obvious before hand-thinning fruit, which limits potential fruit size. Experiments were conducted near Clemson, South Carolina to determine the efficacy of combining Vegetoil~(R) (VO), an emulsified soybean oil adjuvant (93% soybean oil), with Ethrel~(R) (a.i. 21.7% ethephon)for pre-bloom thinning of peach cultivars. 'Contender' in February 2005 and 'Contender', 'Cresthaven' and 'Rubyprince' in January 2006 were sprayed with 10% VO except for 'Rubyprince' (8% VO). Ethephon concentrations were 50, 100, or 150 ppm. Dormant oilat 3% was the control treatment. VO (10%) plus ethephon at 100 and 150 ppm significantly delayed bloom in 'Contender' and 'Cresthaven' in 2006. VO (10%) significantly reduced the number of live flower buds at bloom for these two cultivars, but 8% VO didnot significantly affect 'Rubyprince' flower bud survival. The addition of Ethrel~(R) to the VO spray significantly reduced live flower bud numbers at bloom versus just the VO treatment for 'Contender' and 'Cresthaven', but there were no differences observed among the 'Rubyprince' treatments. Generally, 'Rubyprince' is easier to thin with soybean oil than 'Cresthaven', but the opposite was observed in this study. Chill hour accumulation and temperature at application and VO rates may have differentially influenced cultivar flower bud sensitivity to VO and Ethrel~(R).
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