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- Author or Editor: Duane W. Greene x
YI-1066 is a new blossom thinner that may be useful as an alternative to the presently-used chemical thinners. It was applied as a dilute spray to `Royal Gala' apples at either 475 or 950 ml/379 liters when about 80% of the flowers were open. Browning of flowers and leaves was noted within 1 hour of application. The 950 ml/liter rate reduced fruit set. One YI-1066 treatment was applied at the 475 ml/379 liters rate, and rain started within 10 minutes after the completion of the spray. Although flower browning was noted, fruit set on these trees was increased above that on control trees. The recommended commercial thinning combination, 3 ppm NAA and 600 ppm carbaryl, did not thin. YI-1066 at 950 ml/379 liters caused a significant amount of thinning but it also reduced seed number and increased the number of fruit with solid russet at harvest.
The trend toward planting high density apple orchards continues. Closer tree spacing requires a greater degree of growth control to reduce shading and to prevent the decline in fruit quality and productivity as the planting become older. Chemical, rootstock, pruning, and management techniques will be reviewed that may control growth directly by reducing vegetative growth or indirectly through effects on increasing flower bud formation and fruit set. Pruning and management techniques will be discussed that can selectively reduce vigor in the tops of trees while allowing growth of the less vigorous lower portion of a trees to continue.
Aminoethoxyvinylglycine (AVG) was used in two experiments to control preharvest drop and to improve fruit quality of `McIntosh' apples. AVG application at 25 g a.i./acre (26 ppm) and 50 g a.i./acre (52 ppm) to mature `McIntosh'/M.7 apple trees delayed drop between 1 and 2 days. In another experiment where AVG was applied to `Marshall McIntosh'/Mark apple trees at concentrations between 30 and 120 ppm, drop control also was good. The response was linear. NAA had little or no effect on retarding preharvest drop. In both experiments, AVG increased fruit flesh firmness, retarded ripening, and delayed red color development. The commercial potential of AVG will be discussed.
Proheaxadione-calcium (ProCa) was applied to `Spencer' apple trees at rates between 250 to 750 mg·L–1 after harvest but before leaf fall. The following spring terminal growth was reduced linearly from early petal fall through the growing season to leaf fall. ProCa was applied after harvest and before leaf fall at 500 mg·L–1 to `Spigold' apples. The carryover effect on terminal growth persisted for about 2 weeks after bloom. A combination of 500 and 82.5 mg·L–1 ProCa on `Spigold' in the fall and spring, respectively, reduced terminal growth greater than the individual treatments for about 3 weeks after petal fall. Recent report have shown that ProCa can induce physiological resistance to fire blight and apple scab when applied near petal fall. These data support the suggestion that ProCa may be used as a fall application and the carryover effects may result in early growth control. Potential benefits of the carry-over effects of ProCa for early-season suppression of fire blight and apple scab are discussed.
AVG was applied as the ReTain formulation over three harvest seasons to determine the influence of time of application on drop control efficacy and its influence on fruit maturity of 'McIntosh' apples. Effective drop control was achieved through the commercial harvest season with application of AVG made from 1 to 6 weeks before the anticipated start of harvest for untreated fruit. Drop control extended beyond the normal harvest period when application was made either 2 weeks or 1 week before anticipated harvest. Application made between 6 and 4 weeks before anticipated harvest generally delayed parameters associated with ripening, such as softening, degradation of starch, and development of red color, more than applications made on later dates. While AVG consistently and effectively retarded abscission, the length of time it controlled drop varied from year to year, even when used on similar trees in the same block. Once applied, it required 10 to 14 days before AVG started to retard fruit abscission. AVG controlled drop linearly with increasing concentration. AVG was a superior drop control compound than NAA. Chemical names used: aminoethoxyvinylglycine (AVG), naphthaleneacetic acid (NAA).
Over 225 apple cultivars grown at the Horticultural Research Center in Belchertown have been evaluated for fruit quality and fruit characteristics. Methods used to determine fruit characteristics and organoleptic assessment will be presented. The postharvest potential of the most promising apples will be presented. Two apples ripen about the first of September and show promise for early market. `Sansa' is a medium-sized red apple that ripens about the first of September. It is a high-quality apple with characteristics similar to `Gala'. `Ginger Gold' is a large, firm, mild-flavored, russet-free, yellow apple. `Honeycrisp' is a red apple that ripens in mid-September, before `McIntosh'. It is a large, mild-flavored apple that is sometimes erratic in red color development. It maintains firmness and explosive crispness out of storage better than any other apple evaluated. `Golden Supreme' is an extremely attractive, russet-free `Golden Delicious' type ripening 7 to 10 days before `Golden Delicious'. When ripe it has a very aromatic, fruity flavor. It stores better than `Golden Delicious'. Other apples with merit that have commercial potential include: `Hampshire', `Shizuka', `Cameo', `Creston', `Coop 25', `Coop 29', and `Braeburn'. `Pink Lady' is a very late maturing, new cultivar that is being heavily planted in other areas. Although it does mature here, based upon starch rating, fruit size is small, the flesh is dry and very tart, and taste is only fair.
The lack of pollination and the effects of blossom thinners were simulated by enclosing selected `McIntosh' apple spurs in super-light insect barrier netting at the pink stage of flower development. Fruit set was recorded and fruit size measured at 2- to 3-day intervals from petal fall until initial set. The effects of lack of pollination or the use of blossom thinners on initial set could not be determined with any degree of accuracy until at least 8 days after petal fall. NAA was applied at 8 ppm when fruit were 8.5 mm in diameter. Fruit set and fruit size were taken at 2- to 3-day intervals until the end of June drop. Fruit set on NAA-treated trees was greater than that on check trees for 2 weeks following application. Although NAA ultimately did cause significant thinning, it was not until 3 to 3.5 weeks after application that it was possible to determine with accuracy the thinning response to NAA. However, the thinning response to NAA could be predicted within a week after application, since growth of fruitlets that ultimately abscised slowed 4 to 7 days after the application of NAA. A working model to predict effective pollination and the response to chemical thinners in apples will be discussed.
Pome fruit display a biennial bearing tendency that is characterized by heavy flowering and fruit set one year followed by a year with reduced bloom and fruit set. This tendancy results in a year with heavy cropping with small fruit, and a subsequent year with large fruit and a small crop. Both situations are undesirable. Chemical thinners in the “on” year are frequently used to modify this cropping behavior. Alternative methods to control cropping by flower bud inhibitions will be discussed. Gibberellin application in the “off” year at or soon after bloom will inhibit flower bud formation and encourage moderate flowering. This method of crop regulation has been used infrequently. Gibberellins differ in their ability to inhibit flowering. Therefore, selection of a specific gibberellin and an effective concentration range may provide greater flexibility in controlling flowering. The cytokinins CPPU and thidiazuron inhibit flower bud formation, increase fruit size, and also thin fruit. Appropriate application of these cytokinins will be discussed where beneficial effects on fruit size may be achieved while maintaining a moderate level of flower bud formation.
Chemical thinners can be classified as either blossom thinners or postbloom thinners. Blossom thinners act by inhibit further pollination, pollen germination, or pollen tube growth. At petal fall it is not possible to distinguish between fruit that have been injured by blossom thinners, and those that will persist and continue to grow. The receptacles of blossom thinned fruit do not grow, whereas fruit that has not been treated and that also contain viable seeds, resumes growth within 4 to 6 days, depending upon temperature. Abscission of fruit treated with postbloom thinners does not usually occur until 1.5 to 3 weeks after application. Frequently, it is possible to identify fruit that will abscise and to make an initial assessment of thinning efficacy, within 4 to 6 days following application by measuring fruit growth rate. A reduction in fruit growth by as little as 15% to 20% less than rapidly growing fruit is usually sufficient to assume that the fruit will abscise sometime during the June drop period. The effects of specific chemical thinners on fruit growth and subsequent thinning will be discussed.
An experiment was initiated on mature `Morespur McIntosh'on M.7 rootstock to document the effects of repeated yearly applications of benzyladenine (BA) and naphthaleneacetic acid (NAA) on fruit quality at harvest, the development of storage disorders following regular air storage, and on return bloom. When analyzed over the 4-year period, thinning did not significantly reduce crop load. This result was due in large part to no thinning response one year and very poor set on all trees in another year. Thinners were effective at increasing return bloom over the course of the experiment. BA increased fruit weight but reduced red color compared with NAA treated and control trees. Fruit quality differences at harvests were attributed primarily to crop load effects. There were no fruit quality, return bloom, or storage disorders that could not be explained by treatment effects on crop load or due to previously known effects of individual thinners. The results of this experiment clearly suggest that there are no direct adverse effects following repeated use of either NAA or BA.