ADJUSTMENT OF IDEAL H₂CN₂ CONCENTRATION FOR BREAKING DORMANCY OF GRAPEVINE IN LESS WARM REGION

The objective of this work was to define the ideal doses of H₂CN₂ for bud break of 'Italia' grape in São Miguel Arcanjo, (23°32'W/48°00'S), Brazil, center of the high quality grape region, in comparison with the similar chemical compound traditionally used, calcium cyanamide.

Two experiments were carried out, one in the beginning of the winter (July) and another in the beginning of spring (September). The concentrations of H₂CN₂ were: 0.0M, 0.24M, 0.30M, 0.36M, 0.42M, 0.48M. The concentration of CaCN₂ was 1.67M. The parameters analyzed were: % bud burst, % dormant buds, cluster number and weight of clusters. The Dunnett test was used to compare means of the treatments with H₂CN₂ in relation to CaCN₂, and polynomial regression was used to study the concentrations of H₂CN₂.

The pruning accomplished early winter (July) led to the following results:

1. H₂CN₂ 0.30M, 0.42M and 0.48M was more efficient in dormancy breaking than CaCN₂ 1.67M
2. Spraying cyanamide in increasing concentrations from 0.24M to 0.48M induced a significant effect in increasing percentage of bud break.
3. Increasing concentrations of cyanamide from 0.24M to 0.48M induced a significant effect in increasing cluster number and a quadratic response for cluster weight with a maximum at 0.409M.

The pruning accomplished early spring (September) presented the following results:

1. The calcium cyanamide was as efficient as the hydrogen cyanamide for the studied characteristics: bud burst, dormant buds, number and weight of clusters.
2. Spraying cyanamide in increasing concentrations from 0.0M to 0.48M induced a significant quadratic effect for the characteristics, being a maximum for percentage of bud break, number and weight of cluster at 0.276M, 0.282M and 0.269M respectively and a minimum for dormant buds at the dose 0.267M.

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