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G.A. Cahoon, D.M. Scurlock, and J. D. Lehman

Factorial treatments of vine spacing, shoot density and foliar applications of KNO3 were imposed on 9-year-old Seyval grapevines during 1989. Rows were spaced 3.05 m apart; vines within the row were spaced 1.2, 1.8 or 2.4 m apart and trained to a bilateral cordon. Shoots were thinned to 10, 20 or 30/m of canopy. A solution containing 6 kg of KNO3/379 liters of water was applied as a foliar spray at 2-week intervals between June 1 and August 1, 1989 (5 applications). Each shoot was thinned to one cluster prior to full bloom. Vines spaced at 1.2, 1.8 and 2.4 m produced an average of 4.2, 5.9 and 7.3 kg/vine, respectively (11.3, 10.6 and 9.8 MT/ha). Cluster weight averaged .22 kg; fruit maturity averaged 19.7°Brix for all treatments. Applications of KNO3 increased foliar N, K, Fe, B, Cu and Na, but decreased P, Ca, Mg, Mn, and Zn. As vine spacing increased the concentration of foliar N, P, K decreased. As shoot density increased N, P, K, B, and Cu decreased, while Ca, Mg, Mn and Na increased. The experiment will be repeated in 1990.

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D.C. Ferree, D.M. Scurlock, and J.C. Schmid

`Seyval blanc' and `Vidal blanc' grapevines (Vitis sp.) grown in large containers were root-pruned at different severities and/or stages of development and the effects on growth of both cultivars and fruiting of `Seyval blanc' were determined. As the severity of root pruning increased, stomatal conductance (g s) and transpiration (E) decreased and the number of wilted leaves increased in both cultivars. In both cultivars, root pruning reduced net photosynthesis (Pn) and E for as long as 18 to 20 days, as well as total leaf area and dry weight of leaves and petioles plus tendrils. The reductions were proportional to the degree of root pruning. A similar pattern existed for cane and root tissue of `Vidal blanc'. As the severity of root pruning increased, berry and cluster weight, and titratable acidity (TA) of `Seyval blanc' decreased. There was no effect of root pruning on berries per cluster, soluble solids content (SSC), or pH of the juice. No interaction was significant for any factor between time of root pruning and fruiting measured on `Seyval blanc' vines. Root pruning at bloom reduced leaf area, number of leaves, and dry weight of petioles, trunks, and canes. Root pruning at veraison had no effect on any vegetative or fruit parameters. Fruiting `Seyval blanc' vines had less leaf area and smaller petiole and cane dry weights than did nonfruiting vines.

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G.A. Cahoon, D.M. Scurlock, and J. D. Lehman

Factorial treatments of vine spacing, shoot density and foliar applications of KNO3 were imposed on 9-year-old Seyval grapevines during 1989. Rows were spaced 3.05 m apart; vines within the row were spaced 1.2, 1.8 or 2.4 m apart and trained to a bilateral cordon. Shoots were thinned to 10, 20 or 30/m of canopy. A solution containing 6 kg of KNO3/379 liters of water was applied as a foliar spray at 2-week intervals between June 1 and August 1, 1989 (5 applications). Each shoot was thinned to one cluster prior to full bloom. Vines spaced at 1.2, 1.8 and 2.4 m produced an average of 4.2, 5.9 and 7.3 kg/vine, respectively (11.3, 10.6 and 9.8 MT/ha). Cluster weight averaged .22 kg; fruit maturity averaged 19.7°Brix for all treatments. Applications of KNO3 increased foliar N, K, Fe, B, Cu and Na, but decreased P, Ca, Mg, Mn, and Zn. As vine spacing increased the concentration of foliar N, P, K decreased. As shoot density increased N, P, K, B, and Cu decreased, while Ca, Mg, Mn and Na increased. The experiment will be repeated in 1990.

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D.C. Ferree, S.J. McArtney, and D.M. Scurlock

Vines of container grown `DeChaunac', `Vidal blanc', `Seyval blanc' and `Chambourcin' grapes were subjected to 5 days of 80% shade at prebloom, bloom or 2 and 4 weeks after bloom. Fruit set, cluster weight, berries per cluster and juice components [soluble solids concentration (SSC), pH and titratable acidity] of `DeChaunac' and `Vidal blanc' were not affected by a short period of intensive shade. `Chambourcin' was sensitive to a shade period near the time of bloom for most of the aforementioned factors, while `Seyval blanc' was intermediate in sensitivity. Shot (green, hard, and undersized) berries of `Chambourcin' and `Seyval blanc' were increased by a 5-day period of shade 2 or 4 weeks after bloom. In a second study, container-grown `Chambourcin' on 3309C (V. riparia × V. rupestris) with one or two clusters and `Vidal blanc' with one cluster were subjected to the following light regimes beginning at bloom for 5 weeks: supplemental light, ambient greenhouse light and 30%, 50% or 80% shade. Yield, fruit set, specific leaf weight (leaf dry weight/leaf area), saturation index, and total leaf chlorophyll increased linearly with increasing irradiance. `Chambourcin' juice pH, SSC, leaf chlorophyll a/b ratio, cluster color development and hue angle decreased as irradiance increased, likely related to crop reduction. Responses in `Vidal blanc' followed similar trends, but differences were not as great. Results demonstrate that light is an important determining factor in fruit set of French-American hybrid grapes and fruit set of some cultivars are sensitive to short periods of intense shade.