Abstract
Abstract Total crop load has an inverse relationship with fruit size, while larger fruit size is often demanded by the peach and nectarine markets. Hand-thinning is extremely expensive, and thus, crop load adjustment, using blossom thinners is a crucial practice to ensure production of commercially acceptable fruit size and yield efficiency in stone fruit. In this study, the influence of branched secondary alcohol ethoxylate (Tergitol TMN-6), ammonium thiosulfate (ATS), Crocker Fish Oil, (FO) and a mixture of calcium polysulfides and thiosulfate (lime sulfur) on fruit set and quality attributes in peaches (Prunus persica) and nectarines (P. persica var. nectarina) were studied. All blossom thinners reduced fruit set in 'Summer Lady' peach in both 2016 and 2017. Fruit sets in 'Summer Lady' peach trees with a double application of Tergitol TMN-6 at the rate of 7.5 or 10 mL.L-1, each rate applied at 40% and 80% bloom, were lower than those receiving the same rates of this chemical only at 80% bloom, but they were similar to those receiving a single Tergitol TMN-6 spray at 15 mL.L-1 at 80% or 100% bloom. 'Summer Lady' peach trees receiving Fish Oil at 20 mL.L-1 plus lime sulfur at 25 mL.L-1, once at 40% bloom and again at 80% bloom had lower fruit set as compared to Un-treated Control but the fruit set was higher than those with any Tergitol-TMN-6 spray. Tergitol TMN-6 at 12m.L-1 at 100% bloom or 10 mL.L-1 all stages of bloom reduced fruit set in 'Zee Lady and Snow Giant' peaches. Total yield was proportional to the severity of thinning and final fruit weight. In 'Snow Giant' peach, trees receiving Tergitol TMN-6 at all concentrations and blossom stages had significantly higher fruit weight as compared to the trees of Un-treated Control. Applications of Tergitol TMN-6 at all concentrations at 80% bloom reduced fruit set in 'Red Globe' and 'Elberta' peaches in Utah comparing with Un-treated Control. Overall, it is concluded that efficacy of blossom thinners depends on the rate of thinners, cultivar and stage of bloom development.
Highlights
Hand-thinning is a critical cultural practice that increase the leaf-to-fruit ratio and leads to the production of larger fruit size in apples and peaches, as well as reduction of the biennial bearing in apples [1,2,3,4]
Temperature, bee activity, varietal differences, tree vigor, and spray volume are among factors influencing the effectiveness of blossom thinning in apples and stone fruit [4]
In this study, when the conditions are in favor of heavy fruit set, it seemed that applications of Tergitol TMN-6 at 10 mL.L-1 at 80% bloom or 12.5 mL.L-1 at 100% bloom, led to optimum thinning
Summary
Hand-thinning is a critical cultural practice that increase the leaf-to-fruit ratio and leads to the production of larger fruit size in apples and peaches, as well as reduction of the biennial bearing in apples [1,2,3,4]. Most blossom thinners are caustic and reduce fruit set by damaging different flower parts, including anthers, stigmas, styles, and pollen tubes, and prevent fertilization [4]. Hydrogen cyanamide (Dormex, 50% a.i.) was initially used to reduce dormancy requirement in ‘Florda Prince’ peach [5]. Dormex was found to be an effective blossom thinner for plums [6] and peach [2] in Idaho. Full-bloom applications of Dormex at 2.5 to 3.12 mL.L-1 significantly reduced fruit set in ‘Flavorcrest’ peach [7]. Comparing efficacy of blossom thinners reveled that Dormex was a more consistent blossom thinner for apple and peach than monocarbamide dihydrogen sulfate or sulfcarbamide (Wilthin, 79%, a.i.), 7, oxybicylo(2,2,2) heptane-2-3 dicarboxcylic acid (Endothall, 0.5% a.i.; an aquatic herbicide), and pelargonic acid (Thinex) [2,3]. Endothall at a rate of 1.87 mL.L-1 formulation was found
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