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United States Department of Agriculture

Agricultural Research Service

Title: The Effects of Chill Hour Accumulation on Hydrogen Cyanamide Efficacy in Rabbiteye (Vaccinium Ashei Reade) and Southern Highbush Blueberry Cultivars

item Stringer, Stephen
item Marshall-Shaw, Donna
item Sampson, Blair
item Spiers, James

Submitted to: Small Fruit Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 15, 2003
Publication Date: July 27, 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 (vaccinium ashei reade) and southern highbush blueberry cultivars. Small Fruit Reviews. vol.3(3/4) pp.339-347.

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 â) 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 had 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 H2CN2 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, or 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.

Last Modified: 4/19/2015
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