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  • Author or Editor: G.W. Lightner x
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MARYBLYT is a computer model system that was developed to assist growers when making management decisions regarding the control of fire blight. This disease is potentially devastating to pome fruit orchards and has traditionally been difficult and expensive to control. The collaboration between the Univ. of Maryland and the USDA Agricultural Research Service to develop MARYBLYT is reviewed to provide information that should be considered when such an effort is undertaken to address any research need using computer applications. Specifically, the development of the software for the MARYBLYT system is presented.

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Abstract

This report presents optimal harvest data equations (OHDE) calculated for 6 cultivars for apples at 3 locations in eastern West Virginia. In general, the equations predicted the observed harvest date one day better than the technique of using average calendar days for fruit development. The equations also indicated that bloom date was more important for determining the harvest date than the mean temperature during the growing season. Nonetheless, because of variability between equations, the overall usefulness of using the historical approach to the development of OHDE is limited.

Open Access

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Branch growth of compact (CT) and “Pillar” (PI) peach [Prunus persica (L.) Batsch.], a columnar growth type, and progeny of CT × PI was analyzed. PI trees were distinguished from CT trees by narrower branch angles and relatively fewer and longer branches. CT × PI hybridization produced two distinct classes of trees in a 1:1 ratio—globe shape (GL) and upright (UP). GL trees had a large number of branches, resembling CT trees, but had narrower branch angles. UP trees resembled PI trees, but with wider branch angles. Analysis of seedling growth at 1, 2, and 3 months indicated that height and number of lateral branches could be used to classify UP and GL mature tree form. Branch angle measured at 2 months was important in distinguishing GL from CT seedlings. Such measurements on young seedlings may be used for early selection of growth habit. The reported results indicate that peach tree form, in respect to branching density and branch angle, can be readily manipulated through hybridization of the appropriate growth types. The columnar form of the PI tree suggests its potential for high-density production systems and its use as a parent in developing narrow canopied trees.

Open Access

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A method for large scale evaluation of flower bud hardiness in apricots using a thermal analysis system interfaced to a computer is described. The technique measures the heat released during the lethal freezing of supercooled water within the bud primordia. Nine thermoelectric junctions wired in series were used to monitor the temperature of 10 individual buds. Bud temperature was scanned every 30 seconds and the data recorded on magnetic tape. The data were subsequently transferred to a minicomputer which analyzed and stored data and produced graphics. Computer assisted thermal analysis can accommodate a large number of samples and simplifies handling and storage of data. This technique has applications as a research tool, for determining critical bud temperatures and in screening selections from a breeding program.

Open Access

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In the article “Dry Matter Distribution and Responses to Pruning Within a Population of Standard, Semidwarf, Compact, and Dwarf Peach Seedlings”, by Ralph Scorza, Li Zailong, G.W. Lightner, and Lenard E. Gilreath (J. Amer. Soc. Hort. Sci. 111:541–545, July 1986), Table 2, under the “Variable” column, which reads “Avg length of shoots (cm)”, should read “Avg length of shoots (mm)”.

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Abstract

Ice formation was initiated between –0.6° and –2.6°C in mature Prunus persica (L.) Batsch trees growing in the field. Trees supercooled very little. Ice formation was initiated at several locations in the tree and subsequently spread throughout. The release of the latent heat of fusion following ice formation in the tissue maintained tissue temperatures 1° to 3° above air temperature for several hours and mitigated the tissue's response to ambient temperatures.

Open Access

Abstract

A sampling plan was developed and used along with a modified grading scheme as a tool to predict apple (Malus domestica, Borkh.) fruit quality, thus providing a means to evaluate the impact of orchard management practices on market potential. Apple extra fancy/fancy packout was predicted to within 10% by examining a 100-fruit sample from each of five bins at the submersion tank. Packout loss factors were predicted to within 5% by sampling 100 fruit from each of four bins. A modified Russo/Rajotte grading scheme in chart format proved to be a useful tool for assessing packout losses. An evaluation of downgraded fruit, comparing the grading scheme to grower practice, yielded coefficients of determination ranging from 0.83 to 0.94 for five of six fruit lots sampled. The grower’s marketing intentions and the tendency of packinghouse staff to give more attention to the most obvious defects during grading influenced the ability to predict packout and the severity of loss factors.

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Abstract

Sample sizes for detection of differences of flower bud survival in peach and nectarine [Prunus persica (L.) Batsch] were chosen on the basis of theoretical confidence intervals (Cl) and least detectable differences (LDD) for the binomial distribution. Theoretical Cl and LDD for 1000-bud samples were comparable to Cl and Duncan's multiple range test separation computed from an analysis of variance for 1000 buds, based upon 10 replicates of 100 buds. Variability in survival was a function of eultivar, height of bud in canopy, and bud type. Variability may be minimized by sampling a given bud type (single, double, distal) at >1.5 m above ground level.

Open Access

Abstract

Three-year-old limbs of unpruned standard (ST), semidwarf (SD), compact (CT), and dwarf (DW) seedling peach [Prunus persica (L.) Batsch] trees were separated into component parts at harvest. CT and DW trees had allocated higher percentages of dry matter to one- and 2-year-old branches than ST and SD trees. Although the proportion of dry weight in current season shoots was highest in CT trees compared with the other tree types, fruit dry weight was relatively low. In a separate study ST, SD, and CT trees were pruned and left unpruned, and current season shoot and fruit growth was recorded. Pruning increased the wood dry weight per trunk cross sectional area in current season growth in ST trees and increased the average length of shoots and lowered light penetration in ST and SD trees, but pruning did not affect current season shoot dry weight or length in CT trees. Shoot dry weight and shoot length were greatest in pruned ST trees. The number of shoots was not affected by pruning in any tree type. Total fruit dry weight did not differ with pruning or tree type.

Open Access

Apple packout audits were conducted during 1991 to 1993 to assess effects of five orchard systems (three cultivars, two age groups) on fruit packout and determine if relationships exist between light quality and productivity. Cultivar/rootstock combinations on 1979 T-trellis and central-leader systems had the lowest light levels and relative yields. Trees on either 1979 3-wire trellis, 1986 MIA, or 1985 West Virginia spindle had the highest light transmission, and trees on 1979 or 1985 West Virginia spindle systems had the highest yields. Extra fancy/fancy packouts across systems ranged from 40% to 85%. `Empire', regardless of system, had the highest packouts, and `Golden Delicious' on 1979 or 1986 central leader had the lowest packouts. A regression analysis comparing percentage packout in grades below fancy to percentage full sun indicated that reduced packouts were related to low light conditions. Orchard system influenced the number of fruit downgraded due to color, russet, bruises, bitter pit, cork spot, apple scab, rots, sooty blotch/fly speck, and tufted apple budmoth. Regression analyses comparing defects to field data indicated that bitter pit decreased as yield efficiency increased, and rot and sooty blotch/fly speck incidence were related to low canopy light penetration. Revenue losses were disproportionate to percentage of downgraded fruit because some defects had a greater impact on grade than others. The greatest revenue losses were for russet in `Golden Delicious' on 1986 central leader ($1656.60/acre) and for bitter pit in `Golden Delicious' on 1979 T-trellis ($1067.30/acre). Total losses in returns for individual systems ranged from $453.71/acre for `Empire' on 3-wire trellis to $3145.49/acre for `Golden Delicious' on 1986 central leader. The comparisons of young versus mature system yields and packouts indicate that medium- to high-density vertical or inclined canopy systems are superior to horizontal or low-density vertical freestanding systems. The cost-benefit analyses prescribe areas where management can be changed in existing systems to increase profitability.

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