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Steven J. McArtney and Dick Unrath

Experiments were carried out in the southeastern United States between 1998 and 2006 to evaluate the potential for applications of NAA, Ethrel, or both, in the on-year of a biennial bearing cycle to increase return bloom in apple. Four bi-weekly applications of 5 ppm NAA beginning in mid June (summer NAA) increased return bloom, measured as the percentage of floral spurs in the year after treatment. The level of return bloom on trees receiving a summer NAA program was more than 2-fold higher than on untreated control trees, averaged across seven different experiments. Four applications of 5 ppm NAA at weekly intervals leading up to harvest (August/September) increased return bloom also. Combining 150 ppm Ethrel with summer NAA sprays resulted in an additive effect on return bloom compared to NAA or Ethrel alone. The effect of flower cluster density on return bloom the following year was more negative on control trees than it was on trees sprayed with Ethrel in the previous year. Treatment effects on fruit maturity at harvest were generally neutral, although flesh firmness was reduced in some experiments. NAA or Ethrel sprays in the on-year of a biennial bearing cycle may provide a strategy for achieving more consistent flowering and cropping in apple.

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Steven McArtney, Dick Unrath, J.D. Obermiller, and Ann Green

four trees in each arranged as a randomized complete block design experiment. NAA (5 ppm, Fruitone N) and ethephon (150 ppm Ethrel; Bayer CropScience, Research Triangle Park, N.C.) were applied, either alone or in combination, to fully guarded single

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Robert C. Ebel, Arnold Caylor, Jim Pitts, and Bobby Boozer

Ethrel [(2-chloroethyl)phosphonic acid] was applied at 0, 100 or 200 ppm (mg·L-1) for 3 years to the early maturing `Empress' peach [Prunus persica (L.) Batsch] to determine if bloom delay by Ethrel reduces fruit weight at harvest. Trees were hand thinned at 0 or 3 weeks after full bloom to equalize cropload across Ethrel treatments and to determine if any reduction in fruit weight by Ethrel can be compensated by harvest with earlier thinning. Ethrel at 200 ppm (mg·L-1) delayed bloom by 3, 0, and 7 days in 1994, 1996 and 1997, respectively. Despite bloom delay, Ethrel did not delay harvest or reduce fruit weight. Thus, earlier hand thinning was not necessary. Ethrel did not affect blossom density and was not phytotoxic to vegetative or reproductive organs. These results indicate that even with the shorter fruit growth period of early maturing peach cultivars such as `Empress', there is sufficient time for fruit growth to recover on Ethrel treated trees so that fruit weight at harvest is not reduced.

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Arlie A. Powell, James Pitts, and Bobby Boozer

Early flowering of peach in the Southeast can result in annual crop loss as a result of late winter—early spring freezes. It has been shown in peach and other Prunus that a fall application of ethephon delays flowering several days. However, delayed harvest and smaller fruit size of certain varieties may occur. Hydrogen cyanamide replaces lack of chilling in peach but can also advance harvest date and possibly enhance or maintain fruit size. A randomized complete-block experimental design using 12-year-old `Redhaven' trees was used to evaluate whether hydrogen cyanamide could offset the delayed harvest and smaller fruit size disadvantages of using ethephon without advancing bloom dates. Treatment combinations of ethephon (at 20%, 50%, and 90% of required chilling) and hydrogen cyanamide (at 90% to 100% of required chilling) were applied as whole-tree foliar sprays to near point of drip. Although nonsignificant, there were trends toward hydrogen cyanamide overcoming both smaller fruit size and delayed harvest induced by ethephon.

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Arlie A. Powell, James Pitts, and Bobby Boozer

Early flowering of peach in the southeastern United States can result in annual crop loss as a result of late winter-early spring freezes. In peach and other prunus, a fall application of ethephon delays flowering several days; however, delayed harvest and smaller fruit size of certain varieties may occur. Hydrogen cyanamide replaces the late stage of chilling in peach but can also advance bloom and harvest date while maintaing or enhancing fruit size. A randomized complete-block experimental design using 13-year old `Surecrop' trees was used to evaluate whether hydrogen cyanamide could offset the delayed harvest and smaller fruit size disadvantages of using ethephon without advancing bloom dates. Treatment combinations of ethephon (at 20%, 50%, and 90% of required chilling) and hydrogen cyanamide (at 90% to 100% of required chilling) were applied as whole-tree foliar sprays to near point of drip. Although not significant, there were trends toward hydrogen cyanamide overcoming both smaller fruit size and delayed harvest induced by ethephon. This agrees with an earlier study using `Redhaven'. Dormex negated the late flowering effects of ethephon applied at 20% chilling but did not cause flowering earlier than the control.

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Arlie A. Powell, James Pitts, and Robert Boozer

Early flowering of peach in the southeastern U.S. often results in some annual crop loss as a result of late winter–early spring freezes. It has been shown in peach and other prunus that a fall application of ethephon delays flowering 4 to 7 days and possibly affords increased bud hardiness. However, delayed harvest and smaller fruit size of certain varieties may occur. Hydrogen cyanamide replaces lack of chilling in peach, but can also advance harvest date and possibly enhance or maintain fruit size. A randomized complete-block experimental design was used to evaluate whether hydrogen cyanamide could offset the delayed harvest and smaller fruit size disadvantages of using ethephon without advancing bloom dates over a 3-year period. Treatment combinations of ethephon (at 20%, 50%, and 90% of required chilling) and hydrogen cyanamide (at 90% to 100% of required chilling) were applied as whole-tree foliar sprays to near point of drip. Results exhibited a possible trend toward hydrogen cyanamide overcoming smaller fruit size and delayed harvest.

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Karim M. Farag, Jiwan P. Palta, and Elden J. Stang

The application of ethanol for enhancing effectiveness of ethephon under field conditions on cranberry (Vaccinium macrocarpon Ait.) fruit was tested during three seasons (1986 to 1988). The formulation containing ethephon plus the surfactant Tergitol (0.3% or 0.5%, v/v) and ethanol (2.5%, 5%, or 10%) consistently increased anthocyanin content in the fruit by 28% to 54% over the control. In general, fruit size was not affected by the ethephon treatment containing ethanol and Tergitol. The application of ethephon plus surfactant did not increase the anthocyanin content in the fruit. The presence of ethanol in the ethephon and surfactant mixture, however, consistently enhanced the fruit anthocyanin content by 21% to 40% as compared to ethephon plus surfactant. No adverse effect of various treatments on vine growth or appearance was noticed over the three seasons. Chemical name used: (2-chloroethyl) phosphonic acid (ethephon).

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S.R. Drake, D.C. Elfving, M.A. Drake, T.A. Eisele, S.L. Drake, and D.B. Visser

This study was conducted over two crop seasons using `Scarletspur Delicious' and `Gale Gala' apple trees (Malus ×domestica). The bioregulators aminoethoxyvinylglycine (AVG), ethephon (ETH), and 1-methylcyclopropene (MCP) were applied at various times before or after harvest. Fruit response was evaluated at harvest and after regular atmosphere (RA) and controlled atmosphere (CA) storage [2.0% oxygen (O2) and <2.0% carbon dioxide (CO2) at 0 °C] and quality of whole and juice apple products evaluated. AVG reduced starch loss and ethylene production, enhanced firmness, and reduced cracking in `Gale Gala,' but reduced sensory acceptance of apples and apple juice. ETH intensified starch loss, ethylene production, and reduced firmness, but did not affect `Gale Gala' fruit cracking. AVG followed by ETH reduced starch loss, ethylene production, and cracking and maintained firmness. This combination also aided in sensory acceptance of apples but reduced sensory preference of apple juice. Exposure to postharvest MCP improved flesh firmness retention and reduced ethylene production after both RA and CA storage. MCP either favored or reduced sensory acceptance of whole apples, depending on the particular season, but reduced sensory preference of apple juice. Sensory scores for `Scarletspur Delicious' apples were more strongly modified by bioregulators than were `Gale Gala' apples.

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Don C. Elfving, Gregory A. Lang, and Dwayne B. Visser

Prohexadione-Ca (P-Ca) and ethephon (ETH) were evaluated as potential inhibitors of growth and promoters of early flowering for high density orchard management of sweet cherry (Prunus avium L.) trees on vigorous rootstocks. Single applications (P-Ca at 125 to 250 mg·L-1 active ingredient (a.i.) or ETH at 175 to 200 mg·L-1 a.i.) to young, nonfruiting sweet cherry trees produced short-term, generally transient reductions in terminal shoot elongation, and did not stimulate flower bud formation. Tank-mix applications (P-Ca + ETH) usually produced a stronger, possibly synergistic, reduction in shoot growth rate. Single tank-mix applications either increased subsequent flower bud density on previous season shoots or had no effect; when a second application was made three weeks later to the same trees, subsequent flower bud density on previous season shoots and spurs on older wood increased ≈3-fold over untreated trees. Yield efficiency (g·cm2 trunk cross-sectional area) also increased nearly 3-fold. Chemical names used: (2-chloroethyl) phosphonic acid (ethephon); calcium 3-oxido-4-propionyl-5-oxo-3-cyclohexene carboxylate (prohexadione-Ca); polyoxyethylene polypropoxypropanol, dihydroxypropane, 2-butoxyethanol (Regulaid); aliphatic polycarboxylate, calcium (Tri-Fol).

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Ed Stover, Michael J. Fargione, Christopher B. Watkins, and Kevin A. Iungerman

`McIntosh' apples (Malus ×domestica Borkh.) display a rapid increase in ethylene production as they ripen, resulting in more preharvest drop and accelerated softening compared with other major cultivars. Economic considerations often dictate a choice between delaying harvest to achieve color development or harvesting earlier to avoid excessive fruit softening and drop. We have evaluated the effects of plant growth regulators (PGRs) and summer pruning on this balance. Treatments were applied to trees in the Mid-Hudson region in New York state in 1995 and 1996, and a subset of treatments was applied in the Champlain Valley region in 1996. NAA, applied at 10 mg·L-1 in 1995 and 20 mg·L-1 in 1996, reduced drop on only one sample date in only one of the three trials. Ethephon at 150 mg·L-1 plus 10 mg·L-1 NAA, accelerated ripening and permitted harvest before substantial drop occurred. However, earlier harvest resulted in smaller fruit size, and if ethephon-treated fruit were not picked within a narrow window, rapid drop ensued, and fruit developed a high senescent breakdown incidence during storage. ReTain, containing AVG, at 124 g·ha-1 a.i. delayed drop in all three trials, but its use resulted in firmer fruit after storage in only two of seven comparisons. Use of ethephon on AVG-treated trees enhanced red color but accelerated drop, although it was reduced less than when ethephon was used alone. Severe late summer pruning accelerated red color development, drop and ripening in both years of the study. AVG was more effective for management of `McIntosh' harvest in the cooler Champlain Valley region than in the Mid-Hudson Valley region. Chemical names used: naphthalene acetic acid (NAA); 2-chloroethylphosphonic acid (ethephon); aminoethoxyvinylglycine (AVG).