Submitted to: Small Fruit Reviews
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2003
Publication Date: 9/1/2003
Citation: Stringer, S.J., Marshall, D.A., Sampson, B.J., Spiers, J.M. 2003. Seasonal effects of a late application of hydrogen cyanamide on 'climax' rabbiteye blueberry. Small Fruit Reviews. v.2(4)pp.73-82. Interpretive Summary: Insufficient winter chilling causes certain rabbiteye blueberry cultivars such as 'Climax' to exhibit an abnormal delay in opening of vegetative buds. Hydrogen cyanamide (H2CN2) has been successfully utilized in deciduous fruit crops to enhance leafing in mild winters but flowers of rabbiteye blueberry plants often develop and bloom in the spring before leaves and may be injured by it's usage. Thus, a field study was conducted to evaluate the effects of H2CN2 on flower buds, vegetative bud and leaf development, fruit yield of 'Climax, and the longer-term effects in the year subsequent to its usage. A 1.0% H2CN2 spray increased vegetative bud development and spring foliation. However, when H2CN2 was applied to more developed flower buds or at rates exceeding 1.0% v/v, excessive injury resulted and ultimately translated into a yield reduction. Treated plants had an increased bud load the first year and vegetative bud break was delayed in the Spring of the next year. This information should be useful to Research and Extension Scientist.
Technical Abstract: A field study was conducted to evaluate the effects of hydrogen cyanamide (H2CN2) on flower and leaf buds, foliage, and fruit of 'Climax' rabbiteye blueberry (Vaccinium ashei, Reade), a cultivar exhibiting erratic spring foliation following mild winters. Stems of 'Climax' in several stages of flower bud development were sprayed with H2CN2 (0, 1.0, 1.5 and 2.0% v/v), and effects on leaf development, injury to flower buds, and fruit development were studied. H2CN2 increased the rate of vegetative bud opening, terminal leaf area, and overall vegetative coverage. Damage to flower buds was excessive when H2CN2 was applied at rates > 1.5% v/v or when applications were made on stems at stages 4-5 of flower development. Subsequently, these applications resulted in substantial and significant yield reductions, and rendered fruit more susceptible to late spring frost injury. H2CN2 dramatically increased in the total number of buds developed for the next season's foliage, delaying bud opening in the Spring of 2001. Results of this field study agreed with that of similar controlled environment studies in that when H2CN2 was applied at rates not exceeding 1.0% v/v and when applications are not made at which flower buds do not exceed development stage 2, vegetative bud development is enhanced and damage to flower buds is minimal.