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Release LC (Abbott Laboratories), a commercial formulation of gibberellins, was applied to apricot, cling peach, freestone peach, nectarine, and plum varieties. Application was by commercial airblast sprayer. Fruit firmness was increased in the season of application in all crops. Meta analysis of the data indicated a maximum response for each crop differed over the rate range of 16 to 48 g a.i./acre. Changes in fruit soluble solids were slight. No differences in fruit color were observed. Reduction in flower bud density (thinning) was observed the following season. The reduction in bud density reduced the time required to hand-thin to a commercially acceptable level. A difference in thinning sensitivity to gibberellin was evident between crops.

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Abstract

Ethylene evolution in excised apple (Malus domestica Borkh.) spurs was measured following the application of thinning treatments. Within 1 day (20 hours) of application, ethylene evolution by spurs of ‘Golden Delicious’ trees treated with 15 ppm napthaleneacetic acid (NAA) and 100 ppm (2-chloroethyl)phosphonic acid (ethephon) was 5 times greater than in control spurs, and those treated with 200 ppm ethephon evolved seven times more. Less fruit thinning occurred in response to the application of 100 ppm ethephon than 15 ppm NAA. Increased ethylene evolution was also detected in attached ‘Spatbluhender’ fruitlets 8 hours after NAA treatment.

Open Access
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Abstract

In British Columbia, ‘Bartlett’ pears are thinned with naphthaleneacetamide (NAAm) applied by gun application at 10 μg-liter (w/v) or with air-blast sprayers at 44 g a.i.ha-1, between 13 and 21 days after full bloom. Concern has been expressed by packinghouse personnel about the storage quality of these pears. Higher incidences of breakdown have been suggested, and no controlled experiments have been reported to substantiate or refute such claims. Therefore, a study was conducted during 1980-1983 to assess several quality parameters of ‘Bartlett’ pears thinned by hand and with NAAm.

Open Access

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.

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Abstract

Foliar spray of ammonium phosphate in combination with potassium nitrate during the June drop season, on trees of ‘Wilking’ mandarin (Citrus reticulata Blanco) was effective in thinning and brought about an increase of fruit diameter, reduced fruit acidity, and improved total soluble solids to total acid ratio.

Open Access

Thinning of nectarines and peaches is largely an expensive manual task. We investigated the use of organosilicone surfactants as thinning materials that can be applied by mechanized sprayers. Of the surfactants tested, Silwet-408 (Witco) and Boost (Dow-Elanco) were the most effective thinning agents. Spray concentrations of 0.1% or 0.25% (v/v) applied at 30% and 60% full bloom, or 0.5% applied at 80% to 90% bloom, reduced by 50% the mass of fruitlets that had to be hand-thinned and increased the average weight of harvested fruit by up to 20%. When 0.75% to 1% surfactants were applied at 80% to 100% full bloom, fruit yield was reduced by up to 90%. The sprays did not affect fruitlets that had set already, nor did they cause damage to leaves or young shoots. Open flowers were more susceptible to the surfactants than were flowers at tight-bloom or balloon stage. Ion leakage from both petals and flower bases increased in proportion to concentration of surfactant applied, but there was no increase in lipid peroxidation.

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Loquat (Eriobotrya japonica) belongs to the subfamily Pomoideae, and is an evergreen fruit tree which blooms in fall. Its inflorescence is a panicle. To attain commercial fruit size fruit thinning is done by hand. A chemical thinning trial was performed during the 1999-2000 growing season in Peumo, Cachapoal County, Sixth Region, Chile. Sixteen-year-old `Golden Nugget' loquat trees were treated with naphthalene acetic acid (NAA) at rates of 70, 140, and 280 g·ha-1 (1.0, 2.0, and 4.0 oz/acre), split into two or three applications beginning at early fruit set followed with sprays, 13 and/or 28 days later. Each treatment was applied to four randomly selected trees. At harvest, fruit number was measured in four panicles per tree and in the whole tree. NAA produced a thinning effect closely related to dose, with the highest doses inducing both highest flower thinning and the largest size of the fruit, but the lowest yield per tree. Lower doses produced fruit size and yield similar to those of hand-thinned check trees. Fruit load, expressed as trunk cross sectional area (TCSA), reached 1.8 to 9.1 fruit/cm2 TCSA (11.6 to 58.7 fruit/inch2 TCSA) in treated trees in comparison to 20 fruit/cm2 TCSA (121 fruit/inch2 TCSA) of the nontreated trees. NAA treatments did not affect the number of seeds per fruit. Total dose of 140 g·ha-1 NAA was the most effective in reducing fruit number, whether split into two or three applications. Fruit development seemed to conform to a double sigmoid curve, with a high rate of growth during fall, a lower one through the winter, in order to recover the growth rate in spring until maturity.

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Postbloom sprays of BA thinned `McIntosh', `Delicious', `Golden Delicious', `Mutsu, `Empire', and `Abas' apples. BA at 75 to 100 mg·liter-1 was equal to NAA at 6 to 7.5 mg·liter-1 or carbaryl at 600 to 800 mg·liter-1. BA increased fruit size, flesh firmness, and soluble solids concentration (SSC) on all cultivars evaluated. Since BA is applied during the time when cell division is occurring, it is concluded that the increased fruit size and flesh firmness were due to Increased cell numbers. Increased SSC was not due solely to increased leaf: fruit ratio. Thinning with BA was additive with other chemical thinners and no interactions were found on fruit abscission. In most eases, BA increased return bloom. Chemical names used: N-(phenylmethyl)1H-purine-6-amine [benzyladenine (BA)]; 1-naphthaleneacetic acid (NAA); 1-naphthalenyl methylcarbamate (carbaryl); butanedioic acid mono(2,2dimethylhydrazide (daminozide); (2-chloroethyl)phosphonic acid (ethephon).

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The surfactant “Surfactant WK” (dodecyl ether of polyethylene glycol) was applied to peach trees [Prunus persica (L.) Batsch] at full bloom over 3 years. Blossoms died rapidly so that within 2 days dead blossoms could be distinguished easily from live blossoms or set fruit. There were strong (R 2 > 0.87), linear correlations between concentration of “Surfactant WK” applied and percent blossoms removed and fruit set, which were similar over the 3 years. Trees were hand-thinned according to commercial practices after treatment. There was similar cropload, fruit weight, and yield across treatments at harvest indicating no negative effects by the chemical on productivity. There was only slight limb damage at the highest concentrations of “Surfactant WK,” which overthinned blossoms. We recommend that based on the effectiveness, consistency, and lack of significant phytotoxicity, “Surfactant WK” be reevaluated as a thinning chemical for peach trees.

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Authors: and

Abstract

Fruit retention on several cultivars of peach (Prunus persica (L.) Batsch) was reduced when (2-chloroethyl phosphonic acid (ethephon) at 37.5 to 150 ppm was applied during fruit stage I and the beginning of stage II. Leaf yellowing and early drop as well as gummosis of branches and fruits frequently occurred as side effects. Simultaneous application of gibberellic acid (GA3) at 50 to 100 ppm significantly reduced or eliminated the undesirable side effects of ethephon without altering the thinning response.

Open Access