Effect of frost damage and pruning on current crop and return crop of Pinot Noir

In October 2006, much of the wine-growing area in Tasmania was affected by a series of some of the worst frost events in more than 30 years. Widespread damage left vineyards with blackened shoots and the prospect of a considerably smaller crop, with later maturing bunches from secondary buds contributing to poorer quality wine. In a commercial, spur-pruned Pinot Noir planting, treatments intended to encourage and manipulate secondary bud-burst are imposed and effects on yield recorded. Treatments are imposed 10 days after the frost and include: (i) an untreated control (control) with all damaged tissue left in place; (ii) frost-damaged tissue removed (light pruning); (iii) frost-damaged tissue removed and original spur trimmed back to one bud (medium pruning); and (iv) original (damaged) shoot removed back to compound bud on the spur (heavy pruning). Pruning treatment responses for season 2006-07 show that heavy pruning reduces the current crop with no useful gain in uniformity of ripening. The medium and heavy pruning treatments also reduce pruning weights at the end of the season and all post-frost pruning treatments result in a smaller inflorescence primordia size in dormant buds dissected at the beginning of commercial pruning. In the 2007-08 vintage, the untreated control and the medium pruning treatment have significantly lower bunch numbers than the other treatments. There is also a significant effect of terrain elevation on total yield and the number of bunches in the frost year, with increasing damage lower in the inversion. This gradation in damage does not have carry-over effects into the second season. The results indicate that none of the pruning treatments tested have clear benefits for current or subsequent season production, and that a prescriptive approach to pruning should be avoided when the level of frost damage is inconsistent across vines.