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Dan Ga'ash, Israel David, and Malka Cohen

Blossom thinning trials with AKZO Co. surfactant Armothin were carried out on fruitful peach cultivars Early Grande and Babcock during 1993–94. Effective thinning occurred before “full bloom” (40% to 90% FB) at 3% Armothin, increasing between 2% and 4%. However, an improved fruit distribution of `Early Grande' was achieved by repeated application (35% + 75% FB) at 2%. A second spray at 3%, just after FB, thinned some late-blooming flowers on `Babcock' trees, but a temporary leach scorch occurred, as well as with 4% Armothin (single spray) on both cultivars. For a single spray, the optimal stage was found within 60% to 90% FB, at 3% Armothin. Flower biology studies showed susceptibility of the petals to increasing Armothin concentrations at all stages, but pollen tube penetration into the pistils and subsequent fertilization failed only after an earlier application, before anthesis or pollination of the stigma. Within this range of concentration and timing, no damage occurred to the vital fruit set and to commercial yield, provided that weather conditions were favorable during bloom (and spray). Some corrective hand-thinning (20% to 60%) should be applied to the fruitful trees 3 to 4 weeks later to achieve optimal fruit size at harvest. Blossom hand-thinning is still practical in Israel.

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Thomas M. Kon, Melanie A. Schupp, Hans E. Winzeler, and James R. Schupp

destructive by nature and can cause injury to nontarget tissues. Blossom thinner product development has been limited due to the risk of crop damage and high costs of product registration. More than 150 blossom thinning chemistries have been screened since

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Max W. Williams, Sally A. Bound, Jack Hughes, and Stuart Tustin

Endothall [7, oxybicyclo (2,2,2) heptane-2-3 dicarboxylic acid] is an aquatic herbicide which has potential for use as a blossom thinning agent for apples. Trials conducted in Washington State, New Zealand and Australia on several apple cultivars indicate Endothall is a safe, consistent blossom thinner. Cultivars treated were `Golden Delicious', `Delicious', and `Gala'. Single and repeat applications were used in the New Zealand tests. With multiple applications of Endothall, no fruit marking occurred on any of the test cultivars. In temperate fruit zones with extended apple bloom periods, multiple applications of a low rate of Endothall may he beneficial for reducing fruit set and biennial hearing.

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Frank T. Yoshikawa, G.C. Martin, D. Ramos, and J.T. Yeager

Various rates of Wilthin were applied at full bloom to limbs carrying 150 to 250 flowers to study their activity on blossom thinning of `Loadel' peaches. Wilthin applied at 0.75% and 1.0% significantly reduced fruit set to 29% and 30%, respectively, while the control produced 94%. The effectiveness of the 0.75% rate was dramatic, but it is interesting to note that the 1.0% rate did not lead to excessive thinning nor phytotoxicity on foliage or fruit. More extensive studies need to be done to fully determine the potential of this material. However, these results suggest that further testing of Wilthin on a larger scale is warranted.

Open access

Thomas M. Kon, Melanie A. Schupp, Hans E. Winzeler, and James R. Schupp

, 2008 ). The possibility of using short-duration applications of thermal energy (TS) as a blossom thinning method has not been investigated. Apple blossoms are sensitive to temperature stress. Apple styles and ovules are more sensitive to freezing

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Stephen S. Miller and Thomas Tworkoski

application of an essential oil, represented by eugenol, on blossom thinning, yield, and fruit size distribution. Fig. 1. Chemical structure of eugenol, the active ingredient of several essential oils. Materials and Methods Tests were

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Esmaeil Fallahi, Brenda R. Simons, and Max W. Williams

Effects of hydrogen cyanamide and Wilthin on blossom thinning and the consequences of thinning on fruit set, yield and fruit quality of `Rome Beauty' was studied. A full bloom application of hydrogen cyanamide at the rate of 0.25% (Dormex formulation) or 0.25% of Wilthin both followed by a fruit thinning by Sevin + NAA effectively thinned mature trees of `Rome Beauty' and had a similar effect on fruit set, yield and fruit quality. The effects of these two chemicals at these rates on several aspects of fruit set, yield and quality were similar to the effects of Elgetol. Hydrogen cyanamide, Elgetol and 0.25% Wilthin at full bloom resulted in a higher percentage of single fruit set, thus, less labor for hand thinning. Application of 0.37% Wilthin at 20% bloom or at full bloom resulted in larger fruit size, but induced fruit russetting. Soluble solids of fruit from trees with Elgetol, 0.37% Wilthin at 20% bloom or at full bloom were higher than fruit from other treatments. Hydrogen cyanamide at 0.50% resulted in a satisfactory level of blossom thinning in `Friar' plums.

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Esmaeil Fallahi, Randy R. Lee, and Gary A. Lee

Hydrogen cyanamide (Dormex, 50% a.i.) for blossom thinning `Early Spur Rome' and `Law Rome' apple (Malus×domestica Borkh.) and `Flavorcrest' peach (Prunus persica L.) was applied with air-blast sprayers on a commercial scale. Full-bloom applications of hydrogen cyanamide at 4 pts formulation per 200 gal/acre (1288 mg·L−1) and 5 pts formulation per 200 gal/acre (1610 mg·L−1) significantly reduced fruit set in apple and peach. In `Early Spur Rome', a postbloom application of carbaryl [Sevin XLR Plus, 4 lb a.i./gal (0.48 kg·L−1)] following a full-bloom spray of hydrogen cyanamide increased fruit thinning with a significant increase in fruit size compared to an application of hydrogen cyanamide alone. In `Law Rome', trees receiving a full-bloom application of hydrogen cyanamide followed by a postbloom application of 1-naphthyl-N-methylcarbamate (carbaryl) + naphthalene acetic acid (NAA) had significantly lower fruit set and larger fruit than those in the carbaryl + NAA treatment. Apples or peaches were not marked by hydrogen cyanamide.

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Esmaeil Fallahi

Blossom thinning of `Early Spur Rome' apple (Malus domestica Borkh.) and `Redhaven' peach (Prunus persica L.) with hydrogen cyanamide (Dormex, 50% a.i.), endothalic acid [(Endothal, 0.4 lb a.i./gal (47.93 g a.i./L)], and pelargonic acid (Thinex, 60% a.i.) was studied in 1995 and 1996. Full-bloom applications of hydrogen cyanamide at 2 pt formulation/100 gal (1288 mg a.i./L) and 2.5 pt formulation/100 gal (1610 mg a.i./L) or endothalic acid at 1 pt formulation/100 gal (59.9 mg a.i./L), once at 70% bloom and again at full bloom, reduced apple fruit set. Pelargonic acid was only effective in thinning apple blossoms when applied twice—at 40% bloom and again at full bloom—at 1.5 pt formulation/100 gal (1.12 mL a.i./L) per application. Pelargonic acid marked apples in 1995 but not 1996. Neither hydrogen cyanamide nor endothalic acid marked apples. A single full-bloom application of hydrogen cyanamide, endothalic acid, or pelargonic acid effectively thinned peach blossoms in 1995; however, in 1996, only hydrogen cyanamide at 2.5 pt formulation/100 gal effectively thinned peach blossoms. Peaches did not show fruit marks with any of the peach blossom thinners.

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Brian P. Pellerin, Deborah Buszard, David Iron, Charles G. Embree, Richard P. Marini, Douglas S. Nichols, Gerald H. Neilsen, and Denise Neilsen

of peach and apple trees reduces labour input and increases fruit size HortTechnology 18 660 670 Singh, L.B. 1948 Studies in biennial bearing. IV. Bud-rubbing, blossom thinning and defoliation as possible control measures J. Hort. Sci. 24 159 177