Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2002
Publication Date: December 5, 2002
Citation: Stringer, S.J., Spiers, J.M., Marshall, D.A., Braswell, J. 2002. Effects of hydrogen cyanamide application rates and timing on fruit and foliage of climax rabbiteye blueberry. Acta Horticulturae. 574:241-251. Interpretive Summary: Blueberry varieties require exposure to varying amounts of chilling (hours of exposure to temperatures below 7.2 C) to break floral bud and leaf bud dormancy. Leaf buds may sometimes require greater chilling than flower buds to break dormancy. As a result of this discrepancy, certain early blooming varieties such as the widely grown rabbiteye blueberry cultivar Climax may bloom heavily and set many berries but have too few leaves to support a heavy berry crop. Also, fewer leaves reduce the number of the next season's berry producing buds and leaves. Hydrogen cyanamide (Dormex) is a plant growth regulator that has been used in many fruit crops to increase leafing. A field study demonstrated that 1.0 percent, 1.5 percent and 2.0 percent solutions of hydrogen cyanamide stimulated leaf development in blueberries. However, caution must be taken when applying hydrogen cyanamide, as more advanced berry-producing buds can be injured. The longer-term effects of enhanced leaf production of the health and productivity of Climax plants during subsequent cropping seasons are being studied.
Technical Abstract: A field study was conducted to evaluate the effects of flower bud pruning or utilizing differing rates of hydrogen cyanamide, on development of vegetative and floral buds, as well as on leaf area, vegetative coverage, fruit damage and development, and yield. In this study, hydrogen cyanamide applications increased the total leaf area of leaves arising from terminal leaf buds and also the overall vegetative coverage. Results of this study suggested that in years in which chilling hours are sufficient to result in balanced floral and vegetative bud break and development, cultural practices for promoting the development of leaves of Climax may be of little benefit for enhancing fruit production for that particular season. Results also suggested that application made too late in the season, when as few as 10 percent of flower buds are in stage three of development, excessive flower bud injury and yield reductions may occur. However, the effects of these particular treatments on foliage and fruiting during the following season are yet to be determined.