Performance of Early Fruit-Zone Leaf Removal in Cabernet Sauvignon and Merlot in an Arid Climate

Goals: Our goals were to evaluate how the timing of early fruit zone leaf removal, done between prebloom and post-fruit set, influenced the risk of reduced fruit set, sunburn, and fruit quality in Vitis vinifera Cabernet Sauvignon and Merlot grown in the hot, arid, and irrigated region of eastern Washington State.

Key Findings:

• Fruit set was reduced in Vitis vinifera Cabernet Sauvignon when fruit-zone leaf removal was completed during bloom. Prebloom and postbloom fruit-zone leaf removal did not reduce fruit set.

• Sunburn occurred on fruit on the westside of the canopy in both V. vinifera Cabernet Sauvignon and Merlot. Sunburn severity increased with later-timed fruit-zone leaf removal. Overall, the maximum severity of sunburn was 15% of the cluster surface area.

• Vintage had a greater effect on fruit quality than timing of leaf removal for both varieties. This emphasizes the need to make canopy management decisions that are informed by weather forecasts, to achieve desired management goals.

Impact and Significance: Early fruit-zone leaf removal was traditionally avoided in eastern Washington, in favor of completing the practice after berries have reached pea-size. The later timing of leaf removal, however, can result in sudden exposure of the fruit during the typically warmest and sunniest time of the growing season. Results from this study show that many of the assumed risks associated with early fruit-zone leaf removal, such as extreme reduction in fruit set and sunburn, are not fully realized. This means that early fruit-zone leaf removal could be adopted in this hot, arid climate without a high risk of reduction in fruit quantity or quality.