Gewurztraminer Grapevines Respond to Length of Water Stress Duration

Abstract

Gewurztraminer grapevines planted in 1989 were subjected to one of three durations of water stress (deficits imposed at postbloom, lag phase, veraison) in combination with three vineyard floor management strategies (clean cultivated, total herbicide, permanent sod). Data were gathered on vine performance, fruit composition, and water relations from 1991-96. Yield per vine, cluster weight, and berry weight were reduced linearly with duration of water deficit. Transpiration, stomatal conductance, and leaf water potential were likewise reduced with increased duration of water stress. Titratable acidity decreased and pH increased with duration of water stress, but °Brix was unaffected. Decreasing duration of water stress increased free volatile terpenes (FVT) at harvest, as well as increased potentially volatile terpenes (PVT) at both veraison and harvest. Maintaining a permanent sod tended to reduce all yield components, especially berry weight, but basic fruit composition was unaffected. FVT were highest at both veraison and harvest in berries from clean cultivated plots; however, PVT concentration was highest in berries from permanently sodded plots. Permanent sod treatments displayed lowest transpiration rate and stomatal conductance. Monitoring physiological response (particularly stomatal conductance) of the plant to reduced soil moisture provides a reliable indication of when to relieve irrigation deficits, as opposed to relying on soil moisture monitoring and/or visual assessment of water stress.