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  • Author or Editor: T.L. Righetti x
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Abstract

Differential population levels of pear psylla (Psylla pyricola Foerster) and of twospotted spider mite (Tetranychus urticae Koch) were established in ‘d’Anjou’, ‘Bartlett’, and ‘Bosc’ pear (Pyrus communis) trees by application of selective insecticides and acaricides. Numbers of psylla or mites counted were used to calculate psylla days and mite days by averaging numbers per leaf on successive sampling dates and multiplying this average by the number of days between samples. The N concentration of apparently uninjured shoot leaves of ‘d’Anjou’ and spur leaves of ‘Bartlett’ were negatively related to mite days. The reduction in N induced by mites on ‘d’Anjou’ shoot leaves was large enough to affect fertilizer recommendations based on foliar N. Phosphorus concentration was negatively related to mite days in both shoot and spur leaves of ‘d’Anjou’, but not in other cultivars. Other leaf nutrients were not consistently affected. Densities of the pear psylla were not correlated with foliar mineral nutrient concentrations, although high population levels were not established in this study.

Open Access

Seven-year-old `Royal Ann' cherry trees were given a total of 244 g of actual N as ammonium nitrate depleted in 15N (0.01 atom % 15N) either in March (M), June (J), or both in March and June (Split). The fertilizer was soil-applied to eight single-replicate trees. The following August, leaves from the trees that had the M treatment had 15.3% of their N from the fertilizer compared to 9.6% for the split treatment. Trees that had a J application were not different from the control trees. Even though cherry trees are physiologically active during the late summer months, little N is translocated to the leaves once the crop is fully developed. The percentage of newly acquired N in the fruit is similar to that in the spur leaves. Leaves from the different treatments had similar N contents; therefore, labeled N is the tool of choice to assess the performance of different fertilization practices.

Free access

Current N fertilization practices, where high spring applications are utilized, may lead to excessive vegetative growth. However, high rates may not be required to maximize fruit yield and quality. Therefore, alternative strategies to minimize shoot growth while still providing the N needs of the tree were investigated. Mature `Comice' and `Bosc' pear trees were given one of the following treatments: a spring soil (SS) application of NH4NO3 nitrate at 112.5 kg/ha rate, a similar application in the fall after harvest (FS), a fall foliar (FF) spray of a 7.5% urea solution after harvest (FF), or no N (Control). Trees that received a FF application had the same leaf and fruit N content as control trees, but they yielded more fruit The SS application gave more vigorous trees than FF application. Yield, however, was not different.

A 15N enriched urea solution was applied at harvest as either a foliar spray, soil application, or combination of both treatments to mature `Comice' trees. Flower buds from trees that previously received a foliar treatment had 37% of their N derived from the foliar N application. No labeled N was detected in buds from the soil treatment These results indicate that vegetative and reproductive N requirements of fruit trees may be managed separately.

Free access

Abstract

Boron (B) sprays applied to ‘Barcelona’ hazelnut orchards induced fruit set increases over controls, averaging 23% in 1984 and 17% in 1985. Leaves from B-sprayed trees had higher B contents than controls throughout the season. Amounts of B in young fruits increased two-fold with B sprays, but, unlike leaf values, differences between treated and control fruits disappeared by mid-summer. In the orchards studied, the B content of developing fruits from unsprayed trees was similar even though leaf B content varied widely. Because fruit set increases were obtained in both seasons with B sprays on trees whose leaf values currently are considered excessive, as well as those considered optimal or deficient, guidelines for B recommendation need revision. Boron content in May fruit from unsprayed trees might be universally low for optimum nut development, indicating that annual B sprays may be required. Foliar sprays in April damaged young leaves and shoot tips; thus, delaying sprays until the 2nd week of May is recommended.

Open Access

Relationships between mineral content and corkspot in `Anjou' pears (Pyrus communis) were evaluated in 1985 and 1986. Although there were no significant relationships between mean preharvest fruit mineraI content and corkspot incidence, the postharvest mineral concentrations of corkspotted and normal fruit were markedly different. Corkspotted and normal pear fruit had different Ca and N : Ca ratios in all types of subsamples (peels, opposing tangential slices with peels, opposing tangential slices without peels, cortical tissue plugs from the area next to the core, cortical tissue plugs from the area just inside of the peel, and the cores including seed), based on either dry or fresh weight. The dry-weight basis also revealed differences in Mg concentrations in both years and in B and K concentrations in 1986. Peel concentrations correlated with other tissues and were the easiest subsample to process. Corkspot was absent in either year, with a peel N: Ca ratio below 6.3. A computer model used mean Ca concentrations and standard deviations to estimate the percentage of pears in each orchard that were less than a given threshold level. When the overall average percentage of arbitrarily defined low-Ca pears was small (< 10%), it was difficult to predict the actual number of low-Ca pears from mean Ca concentrations. Therefore, it may not be realistic to expect strong correlations between mean Ca concentration and the incidence of disorders commonly encountered in Hood River, Ore. This situation occurred even when Ca concentrations of disordered and normal pears clearly differed.

Free access

Mature `Comice' pear trees were given 4 l of a 5% urea solution enriched in 15N (0.6 atom percentage 15N) either as a soil application (S), a foliar application with the ground covered to prevent soil contamination (F), or as a foliar application with the ground uncovered (F+S). The treatments were applied in mid-October 1990 to 6 single replicate trees each. The following spring, flower buds from trees that received either F or F+S had 38% of their N from the applied fertilizer. Trees from the S treatment had no label in their buds. In 1991, half of the trees were removed and their components analyzed for total and isotopical N to estimate N recovery. The relative enrichment of different tree parts in 15N was similar for the three modes of application. This suggests that unlike fall foliar applied N, reserve N is more uniformly distributed within the tree. N recovery depended more on tree biomass (r2 = 0.89, P = 0.001) than on the mode of fertilizer application. There was also a positive correlation between tree vigor and fruit N content.

Free access

A microcomputer-based image processing system was used to simplify the large number of visual comparisons required to identify various Corylus spp., cultivars, and clonal accessions using polyacrylamide gel electrophoresis isozyme patterns. Photographs of gels stained for peroxidase, acid phosphatase, and phenol oxidase were digitally captured and selected lanes were enhanced and scanned. The scan data were analyzed to locate bands and normalize their position to that of standards. Such data were plotted and a computer-generated isozyme pattern was displayed. Compressed image data were then stored in a database for subsequent automated isozyme pattern comparisons. Photographic records that were previously used in published reports were reevaluated with the computerized system. Species, cultivars, or clones that were characterized in visual evaluations were similarly characterized using the computer method. Computer evaluations usually identified more bands. Band positions were only rarely different and probably resulted from better normalization relative to standard bands when using the computerized procedure.

Free access