Effects of Early Shoot Trimming of Varying Severity on Single High-Wire Trellised Pinot noir Grapevines

Amid growing concerns over global warming and available management strategies for reducing cluster temperature to prevent overheating and sunburn damage, there is increasing interest in sprawling, non-positioned canopies as an alternative to traditional vertically-positioned ones. However, management of sprawling canopies needs adjustments so that a mostly erect growth pattern is maintained during the season. A three-year study (2009–2011) was carried out to investigate the performance of 15-yr-old Pinot noir grapevines trained to a single high-wire trellis (SHW) subjected to pre-bloom shoot trimming to retain seven (T7) or eleven (T11) main stem leaves. Results showed significant year x treatment interactions: with a low crop and weather conducive to post-trimming lateral re-growth in 2010, trimmed vines had higher leaf area, soluble solids concentration, pH, total anthocyanins and cluster rot incidence than control vines, whereas in 2009 and 2011 the overall must compositional pattern was reversed due to sub-optimal leaf-to-fruit ratios in the trimmed plots. The effects linked to this necessary operation are very much dependent upon unpredictable weather occurring after shoot trimming and, hence, the milder trimming severity (T11) may more successfully balance the need of inducing a still mostly erect canopy while retaining more vine leaves to buffer any weak lateral formation after trimming. The paper provides new and useful knowledge for improved canopy management in trellises having free shoot growth due to absence of foliage wires.