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Stephen C. Myers

Three separate blocks of mature, nonirrigated trees of `Redskin' peach [Prunus persica (L.) Batsch] on `Lovell' rootstock, all uniformly dormant-pruned to an open center, were summer pruned 43, 31, and 21 days before harvest (DBH) in 1988, 1989, and 1990, respectively, and compared to unpruned controls in respect to light penetration and fruit characteristics. Summer pruning consisted of watersprout removal (WSR), selectively including all shoots more upright than 45° on scaffolds from the crotch to the top of the tree. WSR increased photosynthetic photon flux density (PPFD) in the center of the fruiting zone of the canopy to four times the level measured in unpruned trees, but only to an average of 16% of above-canopy PPFD. The greatest effect of WSR on PPFD occurred in the center of the tree, increasing light levels from <10% full sun before WSR to 90% full sun following WSR. WSR resulted in higher PPFD in the center of the tree for the remainder of the season. Fruit ground color and red pigmentation were not affected by WSR. WSR increased the percentage of fruit that exceeded 62 mm in diameter and decreased the percentage of fruit < 55 mm in diameter in 1988 and 1990. In 2 of the 3 years, WSR increased flower count per cm shoot length in the fruiting zone of the canopy.

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Mark Rieger and Stephen C. Myers

“The feasibility of using an over-tree microsprinkler irrigation system for spring freeze protection of `Loring' peach trees [Prunus persica (L.) Batsch] was evaluated under a range of meteorological conditions during Winter 1988-89. Microsprinklers were attached to the underside of polyethylene laterals 2.5 m above ground level and centered over the tree rows. Irrigation rates of 0, 27, 36, and 44 liters/hour per tree were tested on trees trained to an open-center habit using microsprinklers that produced a circular wetting pattern. Microsprinkler irrigation maintained average bud temperature above -2C and 2 to 5C above those of nonirrigated trees under calm conditions, but provided no protection under windy conditions. Flower bud temperatures of irrigated trees were similar for 36 and 44 liters·hour-1, but were slightly lower for 27 liters·hour-1 under conditions typical of spring freezes. Limb breakage due to ice loading was negligible for all application rates, even under advective freeze conditions. Calculated water and energy consumption were reduced by at least 50% and 88%, respectively, by the microsprinkler system, compared to a typical overhead sprinkler system.

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Janet S. Mrosek and Stephen C. Myers

The relationship between cell division, nonstructural carbohydrates and fruit size was investigated using 5-year-old `Encore' peach [Prunus persica (L.) Batsch]. The trees, which were trained to two opposing scaffolds, were selected for uniformity based on tree size and floral bud density. One-year-old shoots ranging in size from 20 to 30 cm were tagged from throughout the canopy. At anthesis, one entire scaffold was thinned of 75% of its flowers, leaving 25% in the mid-section of each shoot. The opposing scaffold served as the control. Samples were taken at three intervals for histological analysis: Anthesis, 30 days, and 45 days after full bloom. Nonstructural carbohydrates were analyzed on samples taken at five intervals: Anthesis, 10, 20, 30, and 45 days after full bloom. Volumetric size increased 29% by 30 days after full bloom, and 64% by 45 days after full bloom. Final fruit size (volumetric) was increased 8% by harvest.

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Paula M. Gross and Stephen C. Myers

One-year old fruiting shoots averaging 50 cm in length were tagged according to naturally-occurring orientations ranging from vertical to horizontal throughout the canopies of dormant `Encore' peach (Prunus persica L Batsch) trees. Following fruit set, tagged shoots were thinned to two or three fruit per shoot. Fruit diameter, terminal shoot extension, and shoot orientation were measured at intervals throughout the season. Fruit were harvested at uniform maturity based on ground color for assessment of fresh weight, diameter, percent red blush, and red color intensity. A linear relationship (p=.001) was found between final fruit size and initial orientation, with fruit diameters 6 percent larger on shoots initially oriented horizontally than those initially vertical. Fruit size differences were not detected until the last two to three weeks of growth. Fruit size response to orientation was found to be independent of light. Red color development was not influenced, probably due to fairly uniform light environments within the canopies. Terminal shoot length was linearly related to initial orientation, with shoots initially oriented horizontally having the least terminal shoot extension. Development of lateral shoot growth in relation to shoot orientation will be discussed.

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Stephen C. Myers, Andrew King and Amy T. Savelle

Mature `Winblo'/Lovell peach [Prunus persica (L.) Batsch] trees in Georgia were treated with five concentrations of D-88, a 79 % to 82 % active ingredient formulation of monocarbamide dihydrogensulfate: 0 (water only), 2.5, 5.0, 7.5, and 10.0 ml·liter-1. All treatments were made by airblast application at 1200 liters·ha-1 when trees were at 95% full bloom. The number of flowers on three limbs per tree was counted 3 days before and fruitlets 25 days following treatment. Regression analysis revealed a linear thinning response to concentration, with 10.0 m1·liter-1 reducing the number of flowers per limb cross-sectional area by 56% over the nonthinned control. Mature `Fantasia' nectarine trees in New Zealand were treated with four concentrations of D-88: 0 (water only), 2.5, 3.75, and 5.0 ml·liter-1. All treatments were made by handgun application to runoff when trees were ≈2 days past full bloom. The number of flowers per limb was counted 6 days before and fruit 62 days following treatment. Regression analysis revealed a linear thinning response to concentration, with 5.0 ml·liter-1 reducing the number of flowers per limb by 55 % over the nonthinned control. Total yield (kilograms of fruit) per tree was the same for all treatments, although fruit size on sprayed trees was larger. No phytotoxicity or fruit finish injury was observed.

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Stephen C. Myers, Steven McArtney, Stuart Tustin, Wendy Cashmore and Richard Mangin

Foliar applications of monocarbamide dihydrogensulfate (D-88, Unocal Chemicals Division) at rates of 0, 2.5 ml/1, 3.75 ml/1 or 5.0 ml/1 were made to mature apple trees of “Fuji”, “Royal Gala” or “Braeburn” on MM106 root-stock. Treatments were applied dilute when spurs were at 95% full bloom. D-88 was applied at 5.0 ml/1 to “Fuji” at three different times during the day (0730, 1400 or 1810) with and without surfactant in an attempt to evaluate the effect of different atmospheric and drying conditions. Fruit set (number of fruit per 100 flower clusters) was determined after natural fruit drop.

D-88 had no effect on fruit set of “Royal Gala” or “Braeburn”. There was a linear effect between D-88 rate and fruit set on “Fuji”, with the 5.0 ml/1 rate reducing set by 30%. D-88 affected the number of fruit at individual fruiting sites, most significantly the percentage of flower clusters setting 3 fruits decreasing with increasing rate. Timing and surfactant had no effect.

Fruit finish, mean fruit weight, seed number and soluble solids concentration were measured at harvest.

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Othmane Mandre, Mark Rieger, Stephen C. Myers, Ray Seversen and Jean-Luc Regnard

Fruiting and nonfruiting `Washington' peach trees were grown in 2.4 (small) or 9-liter (large) containers to determine the influence of root confinement and fruiting on vegetative growth, fruit growth and quality, CO, assimilation (A), and carbohydrate content. Shoot length, fruit diameter, A, and leaf carbohydrates were measured weekly. Thirteen weeks after transplanting, trees were divided into roots, shoots, leaves, and fruit for dry weight measurement. The dry weight of all organs except fruit was reduced by root confinement, and only the weight of stems formed the previous season was not reduced by fruiting. Fruit dry weight was 30.0 g/tree for large- and small-container treatments, causing the yield efficiency (g fruit/g total dry wt) to be 50% higher for confined trees. Fruit red color, weight, and diameter were unaffected by root confinement, but higher flesh firmness and a more green ground color of the fruit surface from root-confined trees suggested that confinement delayed maturity. Vegetative growth was not reduced by lack of nonstructural carbohydrates in confined trees. A was reduced by root confinement on only the first of 11 measurement dates, whereas fruiting increased A on 5 of 8 measurement dates before fruit harvest. Fruit removal reduced A by 23% and 31% for nonconfined and confined trees, respectively, within 48 h of harvest. Leaf starch, sucrose, sorbitol, and total carbohydrate levels were negatively correlated with A when data were pooled, but inconsistent responses of A to carbohydrate content indicated that factors other than feedback inhibition were also responsible for the reduction in A on nonfruited trees. We hypothesized that a physiological signal originating in roots of confined trees reduced vegetativegrowth without reducing fruit growth.

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Stephen C. Myers, Amy T. Savelle, D. Stuart Tustin and Ross E. Byers

Partial thinning of peach (Prunus persica L. Batsch) during bloom to 50% of the necessary level by hand, and followed by adjustment hand thinning at 42 days after full bloom (DAFB) was compared to a similar degree of thinning accomplished entirely at 42 DAFB by hand. Partial flower thinning altered the distribution of fruit by diameter, increasing the percentage of large diameter (≥62.0 mm) fruit harvested compared to unthinned trees or trees thinned entirely at 42 DAFB. Although shoot number per limb was not altered by thinning time, the distribution of shoots by length was affected, increasing the percentage of long shoots (≥20.0 cm). Compared to unthinned trees and trees thinned at 42 DAFB, partial flower thinning increased the subsequent development of flower buds per shoot and the number of flower buds per node. Number of flower buds on the proximal five nodes of shoots 15.0-30.0 cm in length was increased, although not on shoots 5.0-7.0 cm in length. Additional trials established that airblast spray application of AMADS was effective in achieving a similar level of thinning as that accomplished by partial flower thinning by hand in previous experiments. The degree of flower removal exhibited a linear response to chemical concentration. Fruit diameter on chemically flower-thinned trees was greater at adjustment thinning time, when compared to trees thinned by hand at 42 DAFB only. Distribution of fruit at harvest indicated a larger percentage of fruit >65.0 mm in trees which received partial flower thinning in comparison to trees thinned at 42 DAFB only. As a result, overall crop value was increased, based on the commercial processing peach price structure at the time of harvest. Chemical name used: 1-aminomethanamide dihydrogen tetraoxosulfate (AMADS)