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Jason E. Stout, Joan R. Davenport and R. Troy Peters

Drought conditions in the western United States have limited water availability for the irrigation of agricultural products. This can have a dramatic impact on yield and quality of specialty perennial crops, such as juice grapes (Vitis labruscana Bailey). Washington State juice grape industry typically irrigates to 100% of crop-specific evapotranspiration (ETc) throughout the season to minimize yield loss. However, as conditions have limited water availability, growers need a new strategy to cope with the limited water supply. Regulated deficit irrigation (RDI) applies less water than plant ETc and has been shown to improve fruit quality in red wine grapes (Vitis vinifera). The objectives of this study were to evaluate the effects of RDI treatments on the yield and quality of ‘Concord’ juice grapes as compared with current commercial practice. The treatments reduced the amount of water applied between bloom and veraison by 25% (−25%), 33% (−33%), and 45% (−45%) from the control application. The results of this 4-year study initially indicated a dramatic decrease in yield in the −45% treatment (7.5 Mg/ha) as compared with the control treatment (19.2 Mg/ha); however, yield for the RDI treatments recovered in the subsequent seasons and was not statically different from the control. There were no statistical differences in fruit quality between treatments. This indicates that RDI has the potential to decrease water applied between bloom and veraison without impacting fruit quality; however, to avoid a sudden decrease in yield, it would be necessary to gradually reduce water applications over several years.