High Planting Density Reduces Productivity and Quality of Mechanized Concord Juice Grapes

The choice of planting density is a key decision for grapegrowers to make before vineyard establishment, with long-term implications. The field trial described here, with drip-irrigated, machine-pruned Concord juice grapes, tested the effects of two between-row distances (2.44 m and 2.74 m) and four within-row distances (0.91, 1.83, 2.74, and 3.66 m), resulting in planting densities ranging from 997 to 4485 vines/ha, on yield formation and fruit composition. Canopy size, yield components, and fruit composition were measured over six years, starting in year 3 after planting. While in the first cropping season the yield with 0.91 m and 1.83 m vine spacing (11.8 t/ha) was twice that with 2.74 m and 3.66 m (5.6 t/ha), on average over the five subsequent years, the yield of 0.91-m vines was 38% lower (18.2 t/ha) than at the other planting distances (29.2 t/ha). During the last four years, the average yield of vines planted with 2.44 m between rows was 2 t/ha greater than that at 2.74 m. The yield potential and fruit quality of closely spaced vines (0.91 m) was compromised by their vigorous growth, high canopy density, and poor microclimate, which resulted in fewer clusters/vine, fewer berries/cluster, lower cluster weights, and more bunch-stem necrosis. Leaf death in the canopy interior was associated with nutrient remobilization and high potassium and pH in the juice from 0.91-m vines. Juice total soluble solids, titratable acidity, and color remained unaffected by planting density. These results show that planting juice grapes at high density in irrigated and highly mechanized vineyards is detrimental to both cropping potential and fruit quality.