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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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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

In a population of `Delicious' apples (Malus domestica Borkh.) with varying seed number at harvest, fruit size and Ca concentration in fruit increased with seed number. Neither K nor Mg concentration in fruit was related to seed number. In another population of `McIntosh' apples from 50 commercial orchard blocks, the percentage of fruit that developed senescent breakdown, a Ca-deficiency disorder, decreased linearly as seed number per fruit increased. Low seed number is probably a factor contributing to Ca deficiency in apple fruit.

Free access

Several thinning experiments were initiated in 2003 to test the hypothesis that monitoring fruit growth is an appropriate and accurate method to predict final fruit set early enough to apply supplemental thinners if appropriate. A total of eight thinning treatments were applied in Massachusetts and New York. On the day of thinner application 70 to 100 spurs were tagged on 4-8 trees (replications). All fruit within a spur were individually identified and fruit were measured. At 2 to 3 day intervals fruit diameter was measured at a designated point on the fruit. Growth rate of the fastest growing 20 fruit on the untreated trees was used as the criteria to determine growth rate of fruit that would persist to harvest. A fruit on a treated tree was predicted to abscise if growth rate slowed to 50% or less of the growth rate of the 20 fastest growing fruit on untreated trees. Cold weather in 2003 following thinner application slowed the response time to thinners. Thinning treatments were applied to Delicious, Golden Delicious, McIntosh, and Gala at 7-9-mm stage. BA, carbaryl, and combinations of NAA and carbaryl were used. In Massachusetts accuracy of prediction of final fruit set at 7-11 days after application ranged from 87% to 100% with and average of 95% accuracy compared to final observed drop at the end of June drop in July. In Geneva, N.Y., the temperature was so unseasonably cold following application that prediction of final set at 7 to 11 days after application was between 68% and 79% with an average of 74% accuracy. We conclude that prediction of final fruit set following growth rate of individual fruit shows promise as an accurate predictor of final fruit set early enough to apply supplemental thinners if appropriate.

Free access

Multistep chemical thinning programs have been widely recommended in the eastern United States; however, adoption of bloom thinners is limited. With caustic blossom thinners, narrow effective application timings and concerns related to spring frost damage are barriers for commercial use in this region. If effective and safe, use of hormonal blossom thinners for apple would be an attractive alternative. We evaluated the effects and interactions of bloom thinners [6-benzyladenine (BA) and lime sulfur (LS, or calcium polysulfide) + stylet oil (LS+SO)] and a postbloom thinner (NAA) in the context of a multistep, carbaryl-free thinning program across three locations. Experiments were conducted in 2017 and 2018 on mature ‘Gala’ in North Carolina, Massachusetts, and Pennsylvania, USA. In four of six studies, BA at bloom increased the efficacy of postbloom NAA and reduced crop density (P < 0.08). Postbloom NAA generally increased fruit relative growth rate (RGR) and reduced crop density. However, where NAA failed to reduce crop load, there was a negative influence on RGR. BA and LS+SO increased RGR in one of six studies; however, BA was generally ineffective as a blossom thinner, whereas LS+SO was more effective. Nevertheless, BA applied at bloom may have utility as part of a multistep thinning program. As a part of a multistep thinning program, BA applied at bloom may be useful in increasing efficacy of postbloom applications, particularly when use of caustic blossom thinners is not permitted.

Open Access