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  • Author or Editor: D.W. Greene x
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Cytokinin activity from purified xylem sap of ‘McIntosh’ apple trees on Malling Merton 106 (MM 106) rootstocks and from ethanol extracts of MM 106 rootstocks was determined using the soybean callus bioassay. Activity declined in the xylem sap by the third day after removal of the top of the tree. Over 2/3 of the cytokinin activity in young MM 106 rootstocks was found in the young leaves and actively growing stems. Shoots and leaves may be an important source and/or sink for cytokinins in apple trees.

Open Access
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Abstract

(2-Chloroethyl)phosphonic acid ethephon at 150 ppm increased red color on shaded ‘McIntosh’ apples although color development was slow. Eleven days after ethephon treatment 64% of the shaded fruit on 10-year-old semi-dwarf trees met the color standards for U.S. Extra Fancy Grade while only 37% met this standard 14 days after application on the large trees. No shaded fruit on the check trees were U.S. Extra Fancy. Increased red color on ‘McIntosh’ fruit occurred when ethephon was applied either to the fruit or the leaves.

Open Access
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Abstract

Annual applications of 2,6-dichlorobenzonitrile (dichlobenil) from 1969 to 1974 at 17.93 (twice the registered rate) and 22.41 kg/ha reduced trunk circumference increase of young ‘McIntosh’ apple trees for 5 consecutive years. However, the effect of these rates on terminal growth was slight. At rates of 13.44 and 17.93 kg/ha, dicholbenil increased leaf nitrogen only slightly.

Open Access
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Plant response to foliar application of plant growth regulators (PGRs) is often variable, in part due to environmental factors. Weather prior to application is thought to influence cuticle development and thus PGR uptake. For example, in growth chamber studies foliar uptake of 1-naphthaleneacetic acid (NAA) is sometimes increased when fruit trees are placed in low temperature and high humidity several weeks prior to application. Environmental conditions over an extended period of time after application may influence PGR conversion to active form (e.g., ethephon), PGR metabolism, or metabolic factors that affect PGR activity in the plant. The effects of environmental conditions on PGR uptake have been investigated extensively in laboratory studies. In many cases, uptake is clearly increased by high temperatures immediately after application. Laboratory studies report a linear positive correlation between temperature and uptake and greater temperature response above 25 °C (77.0 °F). High humidity and longer drying time often are also reported to increase PGR uptake in laboratory studies. These results are consistent with many grower observations on effects of weather on chemical thinning and have been incorporated into many product labels and extension recommendations. However, relatively few field experiments have been reported in which the relationship between PGR response and environmental conditions were assessed. Wash-off studies have demonstrated that rain shortly after application may reduce efficacy of NAA. Several studies demonstrate environmental interaction with metabolic activity involved in PGR action. For example, shading after thinner application is reported to increase fruitlet abscission and enhance effectiveness of some thinning agents. Chemical thinning of apples (Malus ×domestica) with ethephon is reported to correlate strongly with temperature in the days after application, while studies suggest that higher temperatures after aminoethoxyvinylglycine (AVG) application may reduce control of preharvest drop. However, the stage of fruitlet development at apple thinning often appears to be more important than environmental conditions at the time of PGR application. In addition, field experiments indicate that longer drying times at lower temperatures seem to largely compensate for greater uptake rates at higher temperatures. This paper discusses data from published and previously unpublished experiments in order to understand the effects of environment on PGR response variability.

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A 3-year study was undertaken to compare the effectiveness of mechanical and chemical techniques to enhance flower bud initiation and fruit set on young ‘Delicious’ apple trees (Malus domestica Borkh. Scoring, limb spreading, and growth regulators predictably reduced terminal growth, but only scoring consistently increased bloom. When bloom was increased, fruit set did not always follow. The most effective treatment for increasing fruit set was (2-chloroethyl)phosphonic acid (ethephon) at 1000 ppm plus 1000 ppm succinic acid-2,2-dimethylhydrazide (daminozide). Combination sprays of ethephon plus daminozide show promise for restricting vegetative growth of non-bearing ‘Delicious’.

Open Access
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Penetration of foliar-applied chemicals can be influenced by a number of environmental conditions including: light, temperature, and humidity. These change during the day. 14C-benzyladenine (BA) was applied to the upper or lower surface of McIntosh apple leaves from 6:0 0 to 21:OO hours at 3 hour intervals. The amount of BA entering a leaf over a 24-hour period was not influenced by the time of application. Temperature was correlated with BA retention in the wax layer (correlation coefficients, r=0.06 4 and r=0.70 for the upper and lower surfaces, respectively) and with penetration through the upper surface (r=0.58). BA penetration into the leaf was not correlated with light intensity, relative humidity, or time of droplet drying.

Free access

Abstract

Previous season application of succinic acid-2,2-dimethylhydrazide (SADH) increased fruit set on ‘McIntosh’ apple trees but had no influence on the thinning ability of naphthaleneacetic acid (NAA), naphthaleneacetamide (NAAm), carbaryl (Sevin) or the combination of NAA plus carbaryl.

Open Access

Abstract

Applications of (2-chloroethyl)phosphonic acid (ethephon) on ‘McIntosh’ apple trees (Malus domestica Borkh.) in early August at concentrations of 125 to 500 ppm promoted the climacteric rise in respiration, increased soluble solids, fruit abscission, and red color, and also reduced flesh firmness. Results from ethephon applications in July were variable; in 1974 July applications were more effective, and in 1975 less effective, than treatments applied in early August. The effects of ethephon were reduced when 1000 ppm succinic acid-2,2-dimethylhydrazide (daminozide) was combined with the ethephon. No treatment influenced repeat bloom or set the year following application.

Open Access

Abstract

Sprays of (2-chloroethyl)phosphonic acid (ethephon) applied to ‘Delicious’ apple trees (Malus domestica Borkh.) in July at concentrations of 500 to 1000 ppm shortly after the completion of June drop hastened the respiratory climacteric, and increased soluble solids, watercore and preharvest drop. These effects were diminished when 1000 ppm succinic acid-2,2-dimethyhydrazide (daminozide) was included with ethephon. All concentrations of ethephon increased flesh firmness. Two periods of fruit abscission occurred following ethephon application at high concentrations: shortly after application and immediately prior to harvest. After cold storage, fruit which had received 500 or 1000 ppm ethephon had less scald but a greater incidence of brown core. High ethephon concentrations increased bloom the following spring but had no influence on fruit set.

Open Access

Abstract

Factors influencing the foliar penetration of naphthaleneacetamide (NAAm) were established by following penetration from a glass vial into pear leaf discs (Pyrus communis L. cv. Bartlett). Penetration through the upper surface was linear for 96 hr, whereas, through the lower surface there was rapid penetration for 48 hr followed by a reduced rate. Uptake of NAAm was proportional to the concentration applied. Penetration was not influenced by pH of treatment solutions ranging from 3.0 to 7.0. Increasing temperature from 5–35°C caused a marked increase in penetration with Q10 values ranging between 1.59 to 5.46. Increasing light intensity resulted in increased penetration through the lower surface up to about 300 ft-c, but had no effect on NAAm penetration through the upper surface. Penetration was greater through the upper than lower surface in expanding leaves, but the reverse was true when leaves were fully expanded. Tween 20 and Triton B-1956 (0.1%) increased NAAm penetration through the lower surface, but to a lesser degree than X-77 (0.1%). No surfactant studied enhanced penetration through the upper surface. Penetration from microdroplets was similar to that from solutions in glass cylinders until the droplets dried. Droplet drying resulted in an immediate increase in penetration.

Open Access