Submitted to: Blueberry Research Extension North American Workers Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 7/15/2003
Publication Date: 10/1/2004
Citation: Stringer, S.J., Marshall, D.A., Sampson, B.J., Spiers, J.M. 2004. The effects of chill hour accumulation on hydrogen cyanamide efficacy in rabbiteye and southern highbush blueberry cultivars. Blueberry Research Extension North American Workers Conference Proceedings p339-347. Interpretive Summary: Blueberries are deciduous and cultivars vary in the amount of chilling required to break dormancy. Mild winters are a common occurrence in the Southeast, and often insufficient chilling results in erratic vegetative bud break and leaf development or foliation in the spring. The usage of hydrogen cyanamide (Dormex a^) to promote vegetative bud break is a management tool gaining in importance in blueberry production in this region. Currently, recommendations suggest that applications be made in the winter after "significantly sufficient chilling" has occurred. Results of application timing studies on both rabbiteye and southern highbush blueberries indicated that the efficacy of Dormex in promoting vegetative bud break was greatest when applications were made at the time at which 75% of an individual blueberry cultivar's chilling requirement has been accrued.
Technical Abstract: A controlled environment study was conducted to evaluate the effects of chill-hour accumulation on the time of application and the resulting efficacy of the plant growth regulator, hydrogen cyanamide (H2CN2) in both rabbiteye and southern highbush blueberry cultivars. Application of H3CN2 at the interval in which accruement of 75% of the individual chill-hour requirements of 'Bladen', 'Jubilee', 'Premier', and 'Tifblue' blueberry cultivars resulted in greater vegetative bud break than the 50% chill-hour application timing, of than their untreated checks. The 75% timing also resulted in a significant increase in the terminal growth of stems in 'Bladen' and 'Premier'. Consideration of a blueberry cultivar's exposure to chill-hours in application timing decisions should provide a greater degree of precision in optimizing vegetative bud break with H2CN2.