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Richard Marini*

Six-year-old York/M.9 trees were used to evaluate combinations of chemicals for fruit thinning. In one experiment a factorial combination of 2 levels of carbaryl (0 or 600 mg·L-1) and 5 levels of 6-BA (0, 40, 80, 120, and 160 mg·L-1) were sprayed when fruit diam. averaged 10.5 mm. Carbaryl significantly reduced fruit set, number of fruit/tree, yield efficiency, and crop density, and increased fruit weight. The main effect of 6-BA did not significantly influence any response variable. Two variables were significantly influenced by the carbaryl × 6-BA interaction. In the absence of carbaryl, fruit set was reduced and fruit weight was increased by 6-BA at concentrations less than 160 mg·L-1, but the addition of 6-BA to carbaryl was no more effective than carbaryl alone. In a second experiment, a factorial combination of 2 levels of carbaryl (0 vs. 600 mg·L-1), 2 levels of NAA (0 vs. 5 mg·L-1), and 2 levels of ethephon (0 vs. 450 mg·L-1) were sprayed when fruit when fruit diam. averaged 10.5 mm. Carbaryl and NAA reduced fruit set by about 30%, but ethephon overthinned and reduced set by 65%. When the other materials were combined with ethephon, thinning was similar to ethephon alone. The combination of carbaryl and NAA was no more effective than either material alone. The lowest values for yield, yield efficiency, and numbers of fruit per tree were associated with the combination of ethephon plus NAA. Ethephon was the only material that increased fruit weight.

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Richard Marini

Twenty-eight-year-old `Starkrimson Delicious' trees were spur pruned in 1986 and 1987 and/or treated with BA + GA4+7 in 1986 in an attempt to improve spur growth and fruit weight. Yield, fruit weight, and spur quality characters were recorded for 1986-1989. All treatment combinations failed to improve yield or fruit weight. Although spur-pruning improved spur length, spur bud diameter, leaf area per spur and leaf dry weight per spur, fruit weight was not improved. BA + GA4+7 reduced yield and fruit weight, and increased the number of pygmy fruit in 1986, but had little effect on fruiting for the three years after treatment.

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Richard Marini

In five experiments with `Redchief Delicious' and one with `Braeburn', oxamyl (Vydate 2L) was used alone or combined with other chemicals to thin apples. The thinning response to oxamyl depended on dose. In most cases, oxamyl at 600 mg·L−1 and carbaryl at 900 mg·L−1 thinned trees similarly, but the combination of oxamyl plus carbaryl was no more effective than either chemical alone. The combination of oxamyl plus NAA (2.5 to 5 mL·L−1) was slightly more effective than either material alone. The thinning response to oxamyl and carbaryl was related to the concentration of superior oil added to the spray solution; for both chemicals, adding oil at 5 mg·L−1 or Tween 20 at 1.25 mL·L−1 gave equivalent thinning. Apples on trees sprayed with oxamyl plus oil had a dull finish. Adding Tween 20 at 1.25 mL·L−1 improved the thinning activity of carbaryl (Sevin XLR-Plus) more than oxamyl. Similar thinning occurred whether oxamyl was applied when fruit diameter averaged 4 or 10 mm. On `Braeburn' oxamyl, carbaryl, Accel, and NAA were mild thinners, but all combinations of oxamyl or carbaryl plus Accel or NAA overthinned the trees without improving fruit size. In general, oxamyl at 600 mg·L−1 (2 pints of vydate 2L/100 gal.) and carbaryl thin apple trees similarly, and the efficacy of both chemicals is improved by adding a surfactant.

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Richard J. Campbell and Richard Marini

Light saturation curves were developed for detached, non-fruiting `Stayman' and `Delicious' spur leaves from interior, middle, and peripheral canopy positions throughout the season in 1989 and 1990, respectively. Be inning at bloom, measurements were made every 2 weeks for the first 8 weeks, and monthly thereafter. SLW was calculated simultaneously with photosynthetic measurements. MacArthur-Wilson saturation equations were used with non-linear regression to fit the saturation curves and SLW data, and curves were compared using indicator variables. Even at bloom, saturation curves and SLW differed among positions. The peripheral position bad a greater saturation point and equilibrium rate throughout the season, and the interior and middle positions were equivalent by about 6 weeks after bloom.

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Richard J. Campbell and Richard Marini

Light saturation curves were developed for detached, non-fruiting `Stayman' and `Delicious' spur leaves from interior, middle, and peripheral canopy positions throughout the season in 1989 and 1990, respectively. Be inning at bloom, measurements were made every 2 weeks for the first 8 weeks, and monthly thereafter. SLW was calculated simultaneously with photosynthetic measurements. MacArthur-Wilson saturation equations were used with non-linear regression to fit the saturation curves and SLW data, and curves were compared using indicator variables. Even at bloom, saturation curves and SLW differed among positions. The peripheral position bad a greater saturation point and equilibrium rate throughout the season, and the interior and middle positions were equivalent by about 6 weeks after bloom.

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Richard P. Marini

Mature `Norman'peach [Prunus persica (L.) Batsch] trees were dormant pruned to retain a range of fruiting shoots per tree (71 to 250) during 3 years from 1997 to 1999. About 40 days after bloom each year, fruits on all trees were thinned to similar crop loads, so only the number of fruits per shoot varied. Fruit set and number of fruits removed by hand thinning were positively related to number of fruiting shoots retained per tree. Number of fruits harvested per tree was not related to number of shoots per tree, whereas average fruit weight at thinning and at harvest, and crop value per tree were negatively related to the number of shoots retained per tree. These results indicate that commercial peach producers should consider modifying pruning and thinning strategies. Rather than retaining a large number of fruiting shoots per tree and hand thinning to distribute fruits every 15 to 20 cm along each fruiting shoot, producers should first determine the number of fruits that trees of a given cultivar can adequately size and then perform the thinning operation to obtain the desired crop load. The number of fruiting shoots retained per tree during pruning should be one-fifth to one-seventh of the number of fruits desired per tree, so that five to seven fruits per fruiting shoot are retained after hand thinning.

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Richard P. Marini

Experiments with factorial arrangements of treatments plus one or more other treatment(s) are sometimes analyzed with a one-way analysis of variance (ANOVA) and means are separated with a multiple comparison. A set of single degree-of-freedom contrasts in a one-way ANOVA, provides formal tests for main effects and interactions. Data from a 2 × 3 factorial experiment that also contained a control were analyzed with a one-way ANOVA with a multiple comparison. Results from this analysis were compared to results obtained from a two-way ANOVA, a one-way ANOVA with pre-planned contrasts, a two-way ANOVA with least squares means comparisons obtained with SAS/general linear models procedure, and a regression model with an indicator variable and random blocks obtained with SAS/Mixed procedure. Results and interpretation differed depending on how the data were analyzed and these differences are discussed.

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Richard P. Marini

Three experiments were performed to determine if pruning treatments could reduce the need for peach [Prunus persica (L.) Batsch] fruit thinning without reducing average fruit weight. To determine if dormant shoot heading affected fruit size simply by reducing the number of flowers per tree, all 1-year-old shoots on `Cresthaven' trees were headed by 50% or blossoms were removed from the terminal half of each shoot. At 45 days after full bloom, all trees were hand-thinned to obtain predetermined crop densities. Average fruit weight was highest on trees with blossom removal, but crop value and net profit were highest for nontreated trees. To determine the influence of treatment severity on fruit weight, all shoots on `Cresthaven' trees were blossom-thinned or headed to remove blossoms on varying proportions of each shoot. Fruit set and the number of fruit removed during postbloom thinning decreased as the percentage of a shoot that was headed or blossom-thinned increased. Average fruit weight at harvest and crop value were higher for trees with blossom removal than for trees with headed shoots. Fruit weight and crop value were not affected by the percentage of the shoot treated. In the final experiment, all shoots on `Cresthaven' trees were headed by 50% or were not headed. Heading of shoots reduced fruit set, number of fruits removed at thinning, and thinning time per tree, but yield, crop density, and average fruit weight were not affected by heading. Profit was increased by shoot heading one of the 3 years. Results from this study indicate that heading peach shoots by 50% while dormant pruning can reduce thinning costs without reducing fruit size, but a similar level of labor-intensive blossom removal may reduce postbloom thinning costs and improve fruit size.