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Duane W. Greene

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.

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Duane W. Greene

Plant growth regulators (PGRs) play an important commercial role in horticulture. Although often expensive, they are generally used on high value crops where the costs can be retrieved through the increased value their usage creates in a given crop. The impetus for development of new PGRs is generally initiated by the agrochemical industry where they perceive a need that has a profit potential, whereas the motivation for the development of a PGR by researchers is largely to aid the industry they serve. University and government researchers initially follow a prescribed protocol early in the development process, but once they have gained personal experience with a PGR, further research is often guided by personal observations and keen technical insight. During the development and evaluation process, university and government researchers are optimistic, and negative effects are generally viewed as challenges, that can and will be overcome. Discussion and effective communication are critical components in the overall development of a new PGR. Researchers generally exchange information very freely, unless restricted from doing so by a nondisclosure or other contract agreement. The underlying goal for university and government researchers is to get approval of a new PGR product and/or use that will allow growers to produce a high quality product for consumers with an improved profit margin for growers. Development of new PGRs is undergoing major change that unfortunately will lead to the development and registration of fewer compounds. There are not as many agrochemical companies, there are a decreasing number of university and government researchers, and diminishing funds available to support the development of new PGRs.

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Duane W. Greene

Experiments were conducted to evaluate abscisic acid (ABA) and the combination of ABA and benzyladenine (BA) as a thinner on ‘Bartlett’ pears. Application of 500 mg·L−1 ABA at bloom, petal fall, and at the 10-mm stage resulted in significant fruit thinning at all timings. Application at the 10-mm stage nearly defruited the trees. Rates of ABA between 50 and 500 mg·L−1 were evaluated at 10 mm and the thinning response was quadratic and highly significant. Rates as low as 50 mg·L−1 thinned. BA at 150 mg·L−1 at the 10-mm stage did not thin and when combined with 250 mg·L−1 ABA, no additional thinning was observed, but extensive thinning was done by the ABA alone. When thinning with ABA was achieved, return bloom was also enhanced. Thinning with ABA generally resulted in larger fruit, greater flesh firmness, and higher soluble solids. The russet seen on ABA-treated fruit was attributed primarily to the surfactant used. Extensive leaf yellowing and leaf abscission were noted after ABA application, especially with the 250 mg·L−1 and 500 mg·L−1 and this was considered commercially unacceptable. BA was unable to reverse or modify the leaf yellowing and abscission caused by ABA as it has been shown to do with other plant species.

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Duane W. Greene

Regulation of biennial bearing in pome fruit is usually accomplished by chemically removing fruit during the “on” cycle. The advantages and disadvantages of regulating biennial bearing by inhibiting flowering in the “off” cycle were discussed. Gibberellins and the two phenyl urea cytokinin-like compounds, thidiazuron and CPPU have been shown to inhibit flowering in pome fruit. It was concluded that inhibition of flowering with commercially available gibberellins was not a commercially acceptable approach to regulate biennial bearing. The inhibition of flowering was erratic, fruit thinning and increased fruit set could not be predicted, and seed abortion following gibberellin application could predispose fruit to reduced postharvest life because of reduced calcium uptake. Regulation of flowering by inhibiting flower bud formation appeared to be a viable way to regulate cropping on nonbearing tress or trees that were not carrying a crop.

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Duane W. Greene

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Duane W. Greene

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.

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Duane W. Greene

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.

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Duane W. Greene

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.

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Duane W. Greene

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.

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Duane W. Greene

BAS-125 10W is a new plant growth retardant that was evaluated on `McIntosh' apples to control excessive vegetative growth. When applied at concentrations between 0 and 375 ppm, it significantly reduced terminal growth. As a result, light penetration into the tree was increased and fruit at harvest had more red color, and more were graded into the US Extra Fancy category. BAS-125 increased fruit set; thus, fruit were smaller, but firmer, at harvest. Treated fruit were firmer and had less decay following 20 weeks of regular air storage. Several different thinning strategies were employed to thin BAS-125-treated `Delicious' trees. In one experiment, the best thinning treatment was a combination spray containing 10 ppm NAA plus carbaryl at petal fall followed by 8 ppm NAA when fruit size averaged 10 mm. The best treatment in another experiment was a Wilthin application at 80% bloom followed by 8 ppm NAA plus carbaryl at petal fall. Recommendations for the successful use of BAS-125 10W in the Northeast will be discussed.