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Arlie A. Powell and Ed Tunnell

Lack of winter chilling (480 hrs. at or below 7.2°C by 02/28/89) occurred along Alabama's Gulf Coast in the winter of 1988-89. Varieties requiring 650 hours of chilling or more were under stress. To evaluate hydrogen cyanamide (HC), a product used world wide to replace part of some fruit plants chilling req., a study was conducted along the Gulf Coast using Bicentennial (700 hr.), Sentinel (850 hr.) and Loring (900 hr.) peach varieties. Full tree sprays (applied to drip with handgun) using 0, .5 and 1% a.i. plus .25% × 77 were applied 03/01/89. Fruit buds were dormant to slight swell when sprayed. HC greatly enhanced rate and % of leaf bud break at the 1% conc., for all varieties. Rate and % of flowering were significantly increased at 1% conc. in Loring and Sentinel but nearly all fruit dropped. Flowering, yield and fruit size of Bicentennial-were significantly improved at .5 and 1% conc. HC was effective in replacing lack of chilling in this variety.

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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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W.A. Dozier Jr., A.A. Powell, A.W. Caylor, N.R. McDaniel, E.L. Carden, and J.A. McGuire

Hydrogen cyanamide (Dormex) treatments were applied to 17 insufficiently chilled peach and nectarine cultivars ≈6 weeks after normal budbreak. Treatment effectively induced vegetative budbreak and reduced shoot dieback. The responses to Dormex treatments were linear, with the 2% rate being more effective than the 0 and 1% rates in most cases.

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Nabil R. Elsherbini

Dormex (aqueous solution of 48% hydrogen Cyanamid) was applied by the end of December at 2%, 4%, and 6% in the first season and at 3%, 4%, and 5% in the second season to 1-year-old shoots of MM.106 apple rootstock. Dormex at 4%, 5%, and 6% increased significantly the percentage of bud burst, stool diameter, stool length, internode length, and leaf area; moreover, it decreased the number of days required to reach 50% bud burst. However, Dormex at 4% and 6% enhanced the stool Grand Period of Growth (GPG) by 1 and 2 months, respectively, compared with the untreated plants. Dormex treatments resulted in a significant increase in stool content of N, Ca, and Zn.

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Marja Rantanen and Pauliina Palonen

was not treated. For hydrogen cyanamide treatment, the commercial dormancy-breaking chemical, Dormex (a.i. hydrogen cyanamide 520 g·L −1 ; Degussa Ag, Trostberg, Germany) was diluted to a 1.04% solution of the a.i. Canes were sprayed to runoff with a

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Gerard Krewer, D. Scott NeSmith, and Ben Mullinix

Poor blueberry leaf development is a serious problem in medium and low chilling regions which leads to smaller, later ripening fruit and reduced bush vigor. Dormex (hydrogen cyanamide) and Promalin or Accel (6-benzyl adenine plus gibberellins A4 and A7) were used in the experiments. Dormex 1991-1995 trials with applications at the end of the dormancy period (February) looked promising but were not uniformly successful. In 1996, applications were made starting in mid-dormancy (early-mid January) about 6-8 weeks before normal bud break. Spring vegetative bud development was greatly accelerated with minimal advance in flower development. Mid-dormancy Dormex rates of 1.5% to 2% appear promising. Dormex application after bud break or at excessively high rates will kill flower buds, but has excellent potential as a bloom thinning agent for juvenile blueberry plants. Promalin or Accel applications post bloom significantly accelerated spring leaf development. Late summer applications of Promalin significantly increased fall growth and number of side shoots.

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Esmaeil Fallahi

Effects of various concentrations of Dormex (hydrogen cyanamide, a.i. = 49%), pelargonic acid and endothalic acid, applied at 60% and full-bloom, on fruit set and yield of `Early Spur Rome' apple and `Redhaven' peach were studied over 2 years. A full-bloom application of Dormex at 0.25% and 0.31% (% formulation) alone or 0.125% endothal followed by a post-bloom thinner reduced fruit set and increased fruit size in apple. A double application of endothal at a rate of 0.125%, once at 70% bloom and again at full-bloom, also was effective in thinning and increased fruit size in apple. Pelargonic acid was effective in thinning in apple when applied at a rate of 0.187% at 60% bloom and again at full-bloom. Return bloom in apple was better when blossom thinners effectively thinned blossoms. Dormex application at a rate of 0.31% at full-bloom showed the highest return bloom in apple. All three chemicals were effective in thinning in peach when they were applied before complete fertilization. However, only 0.31% Dormex application at full-bloom was effective in thinning peach when a high rate of fertilization had taken place.

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Bruce W. Wood

We gratefully acknowledge SKW Trostberg AG of Germany for its generous donation of Dormex. Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the produce by the U.S. Dept. of Agriculture and does not imply

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Arlie A. Powell and Karl Harker

It is always challenging to develop innovative Extension programs delivery methods. The development of a winter chilling model (Modified 45) for Alabama, the evaluation of a growth regulator (Dormex—hydrogen cyanamide) to replace lack of chilling in peaches and the establishment of a computerized weather program allowed us to create a superior expert program for grower application. Access through a personal computer is all that is required to monitor chilling accumulation and determine the most ideal time for application of Dormex (which is very critical). This information (formerly available from NWS) is now accessible through a private weather firm. The development of a chilling hour/heat unit (growing degree hour) for peaches is showing promise of providing growers still another useful product (via their PCs) in improving orchard management via better timing of practices.

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K.G. Weis, S.M. Southwick, J.T. Yeager, M.E. Rupert, R.E. Moran, J.A. Grant, and W.W. Coates

In continuing trials (1995-current), we have used a variety of treatments to overcome inadequate chilling, coordinate bloom, improve leaf out and cropping, and advance/coordinate maturity in sweet cherry, cv. Bing. Treatments have included hydrogen cyanamide (HCN, Dormex) and various surfactants or dormant oils combined with calcium ammonium nitrate (CAN17). Chill hour accumulation, (required chilling for `Bing' = 850 to 880 chill hours) has varied greatly in each dormant season from 392 (Hollister, 1995-1996) to adequate, depending both on the season and location (central valley vs. coastal valley). In 1998, 4% HCN advanced budbreak significantly compared to any other treatment, although other chemical treatments also were more advanced than the untreated control. Dormex advanced completion of bloom 11% to 40% more than other treatments, although other dormancy-replacing chemicals were at least 16% more advanced in petal fall than the untreated control. Dormex contributed to slightly elevated truss bud death, as did 2% Armobreak + 25% CAN17. In 1998, fruit set was improved by 2% Armobreak + 25% CAN17 (79%) compared to the untreated control (50%); all other treatments statistically equaled the control. Fruit set was not improved by Dormex, although bloom was advanced by a few days in this treatment. As fruit set was increased by treatments, rowsize decreased (as did fruit weight), as expected, but no treatment resulted in unacceptable size. In 1997, fruit set was also improved by 2% Armobreak + 25% CAN17; however, fruit set was so low overall in that year that no real impact was found. In 1997 and 1998, 4% HCN advanced fruit maturity compared to other treatments, with darker, softer, larger fruit at commercial harvest. These and additional results will be presented.