Cordon Renewal Strategies for Declining Merlot Grapevines

Goals: Some of the older vineyards in Washington have been exposed to recurring winter freeze events. Over the years this has resulted in gradual vine decline and reduced yields, prompting growers to consider vine renewal or replanting strategies. Unlike vineyard replanting, successful cordon renewal may result in a full crop within 1 to 2 years. The purpose of this study was to evaluate the potential of four different cordon renewal strategies to revive an aging and declining, cordon-trained and spur-pruned Merlot (Vitis vinifera) vineyard.

Key Findings:

• None of the cordon renewal strategies tested succeeded in restoring adequate vigor in these vines. However, retaining three short canes (5 to 8 buds each) per cordon increased 3-year average and cumulative yields compared with cordon removal, disbudding, and standard spur pruning. Higher yields were mainly due to higher numbers of clusters as a result of higher numbers of fruitful shoots.

• Cordon removal and retraining led to more uniform recovery than the other strategies, but no yield during the first year and intermediate yields during the next 2 years made this strategy economically less attractive than the short-cane approach. Complete disbudding of the cordon to encourage renewal of spur positions resulted in yields that were no better than those obtained with continued standard spur pruning. Disbudding also led to bushy growth initially, which may increase the cost of canopy management during the first year.

• In the first year the low-yielding disbudding treatment resulted in somewhat higher fruit sugar accumulation. Otherwise fruit composition was similar in all four pruning treatments, and the slight differences that were occasionally observed were within the expected range of technological maturity for high quality fruit.

Impact and Significance: A 3-year pruning trial conducted in a declining, cordon-trained Merlot vineyard indicated that retaining 3 short canes (5 to 8 buds each) resulted in higher crop production than other winter pruning methods. Although adaptive pruning strategies may have some potential to delay the need for replanting in vineyards that have incurred cumulative cold injury, such strategies may only be effective in conjunction with other cultural practices that enable vines to maintain or regain sufficient shoot vigor.