Removal of flower buds, flowers or young developing fruit in early spring is important to increase peach fruit size. Peach growers generally wait until ~ 30 days after full bloom to start hand-thinning fruit, which often reduces potential fruit size.Experiments were conducted in commercial peach orchards in South Carolina to determine the efficacy of food grade, soybean oil (SO) used with an emulsifier and Vegetoil (VO), an emulsified soybean oil, for pre-bloom thinning of difficult-to-thin peach cultivars. Cultivars were selected and sprayed in January or February using rates of 6, 7, 8, 9 or 10% by volume of SO or VO. Dormant oil at 2 or 3% was the control treatment. Bloom was either delayed or advanced by SO and VO depending on cultivar and year. SO and VO significantly reduced the number of live flower buds at bloom in some cultivars in some years. SO and VO also significantly decreased hand-thinning costs and for some cultivars improved fruit size and commercial pack out. Although pre-bloom SO and VO treatments were variable in efficacy, in every year treatments were applied, one or more of the dormant soybean oil applications significantly increased net returns for the grower in that orchard. 'Blazeprince' and 'Fireprince' cultivars were easier to thin with VO and SO than were 'Goldprince' and 'Summerprince'.
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