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.
The lowest flower in the pear (Pyrus communis L.) cluster usually develops and blooms first and also has a greater sink potential. For this reason, resources are preferentially utilized by the lowest fruit, and this is also one of the reasons why most thinning practices tend to favor their set. However, it is not always possible to perform selective thinning. This study was undertaken to determine if hindering pollination in the most developed flowers in the cluster influences yield or quality compared to that obtained in a whole open-pollinated cluster. The treatments were made in `Blanquilla' (Spadona, Agua de Aranjuez) and `Conference' pear within a wide range of flower densities for each cultivar. Pollination was hindered by cutting off the flower styles. The factor tested was style removal intensity (SRI). Treatments consisted in removing the styles of two, four(always the most developed), or all flowers in each cluster. Flower density was used as a covariate in an analysis of covariance to account for differences in flower densities in response to SRI treatments. In all experiments the covariate was not significant; therefore, SRI effect was not affected by flower density. `Blanquilla' and `Conference' had similar responses to treatments, so that when at least three flowers are susceptible to be openly pollinated, fruit set, seed content, and cluster yield were similar to control clusters, therefore the growth potential of fruit from partially damaged clusters in their most developed flowers is similar to undamaged open pollinated clusters. The reduced set of parthenocarpic clusters implies yield reductions ranging between 40% and 60% in `Conference', and up to about 60% in `Blanquilla'.
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.
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.
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.
The influence of temperature and leaf maturity on ethephon-promoted abscission was examined by simultaneously applying either ethylene (10.5 μl·liter-1) or ethephon (0 to 4 ml·liter-1) to potted Camellia plants at four constant temperatures (10 to 30C). The abscission rate (time to 50% abscission) and extent of abscission of leaves, and vegetative and floral buds was measured. Increased temperature promoted the rate and extent of ethephon-promoted abscission and increased ethylene-promoted abscission rate of all organs of Camelliu. Lower temperatures reduced the abscission rate after ethephon application more than that following ethylene application. Sensitivity to ethephon was greater for leaves on newly extending shoots, although once shoot elongation and leaf expansion had ceased, leaves became less sensitive. Ethephon sensitivity increased progressively with maturation over the following 2 years. Optimal thinning of floral buds. at low temperatures required high ethephon concentrations, while at high temperatures, low ethephon concentrations were optimal. The influence on abscission of the time of year when ethephon was applied, is suggested to be due to tissue maturity, which affects tissue ethylene sensitivity, and temperature, which affects ethylene release from ethephon and tissue response to ethylene. Chemical name used: (2-chloroethyl) phosphoric acid (ethephon).
This study was designed to characterize the mechanisms of N-stimulated peach Prunus persica (L.) Batsch productivity. The effects of N fertilization on potential assimilate availability (source capacity) and on the growth capacity of individual fruit (sink capacity) were assessed. On heavily thinned trees, fertilization did not stimulate fruit growth rates relative to those on nonfertilized trees, suggesting that fruit growth rates were not assimilate-limited throughout the period of fruit development. However, N fertilization resulted in a longer fruit development period and increased the growth potential of individual fruit by 20% (fresh mass) and 15% (dry mass) vs. controls. In unthinned trees, N fertilization increased total fruit yield by 49% (fresh mass) and 40% (dry mass) compared to the unthinned, nonfertilized controls. N fertilization increased total fruit yield per tree in unthinned peach trees by extending the fruit development period and thus increasing the amount of assimilate accumulated for fruit growth. The fruit development period was prolonged both by assimilate deprivation associated with increasingly higher crop loads and by N fertilization. Thus, the prolongation of the peach fruit development period by N-fertilization appears inconsistent with the role of N in increasing assimilate availability for fruit growth. We conclude that N fertilization stimulates peach yields by increasing the period for fruits to use assimilates (sink capacity). The effect of N on assimilate availability was not directly evaluated. The timing of fertilizer N availability did not influence fruit growth potential.
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.
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).
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.