Timing and concentration of hydrogen cyanamide affect blueberry bud development and flower mortality

Abstract

The effects of hydrogen cyanamide (H2CN2) sprays on vegetative and reproductive bud growth and development were evaluated for 'Climax' rabbiteye (Vaccinium ashei Reade) and 'Misty' southern highbush blueberry (V. corymbosum L. hybrid). 'Climax' plants were sprayed with 0% or 1% H2CN2 (v/v) at each of several time intervals or flower bud growth stages following either 270 or 600 hours of artificial chilling. 'Misty' plants were sprayed with 0 %, 1%, or 2% H2CN2 (v/v) immediately after exposure to 0,150, or 300 hours of artificial chilling. H2CN2 application to 'Climax' plants at 3 days after forcing (DAF) and at 10% to 30% stage 3 flower bud development dramatically accelerated leafing, and only minimal flower bud damage was observed at these application times. For 'Misty', vegetative budbreak was increased and advanced by both H2CN2 spray concentrations, regardless of pretreatment chilling levels; the number of vegetative budbreaks per plant increased with increased concentration. Timing of anthesis did not appear to be affected by H2CN2, but fruit maturity was hastened. Increased pretreatment chilling also hastened fruit development. This effect on maturity appears to be due primarily to increased and accelerated vegetative budbreak, which probably increased leaf: fruit ratios. Greater flower bud mortality from H2CN2 occurred in nonchilled plants than in those chilled for 150 or 300 hours, especially at 2% H2CN2. These results indicate that H2CN2 has potential value in stimulating vegetative bud development, which potentially hastens maturity in blueberries grown under the mild winter conditions of the Southeast. However, spray concentration and timing of application will be critical to successful use of this compound.