In its 2018-19 fiscal year, the Oregon Wine Board of Directors granted $437,500 to researchers for nine projects with the potential to advance quality grape growing and winemaking in Oregon. The update below is the first in a series to let you know about the status of these projects. 

Dr. Alexander Levin is a viticulturist at the Southern Oregon Research and Extension Center, an assistant professor in the Department of Horticulture at Oregon State University, and a core faculty member of the Oregon Wine Research Institute. He has prepared the update below. This project also receives funding from the Oregon Department of Agriculture, Rogue Valley Winegrowers Association, OWRI and the Agricultural Research Foundation.

Determination of pre- and postveraison water status targets for deficit irrigation of Pinot noir in a warm climate

Project objectives:
The overall objective of this research is to determine early- (preveraison) and late-season (postveraison) vine water status targets to optimize irrigation scheduling in warm climate Pinot noir vineyards. Specific objectives are to:

  1. Irrigate vines at various fractions of crop evapotranspiration (ETc) pre- and postveraison to create a range of water stress levels during both periods.
  2. Determine crop yield and quality parameters at harvest.
  3. Produce replicated wines for each treatment and subject them to sensory evaluation.
  4. Correlate crop yield and quality and wine sensory data with irrigation rates and associated water status values.

Importance to the Oregon wine community:
While Pinot noir has traditionally been cultivated in cooler and wetter growing regions of Oregon, new plantings are occurring in warmer and drier sites that may require supplemental irrigation. Consequently, many growers are uncertain about how to properly irrigate Pinot noir grapevines to achieve their desired production goals. Providing them with more information regarding the effects of water stress on vine performance is necessary for the optimization of irrigation management strategies that will simultaneously conserve freshwater resources and improve Oregon Pinot noir fruit and wine quality.

Progress so far:
The second year of this two-year field experiment was completed in 2018. Eight irrigation treatments at rates ranging from 25 to 100% ETc were imposed in both seasons to the same vines. As of this writing, analyses of 2018 fruit quality data are nearing completion, and wines have been produced and are awaiting sensory analyses. All fruit and wine analyses of 2017 data have been completed.

Cluster number per vine was higher in vines that experienced water stress postveraison. Treatments did not consistently impact berries per cluster or cluster size between years. Berry size was negatively correlated with water deficits during both periods, though the response was not statistically significant. Accordingly, vine yields correlated better with cluster number per vine compared to cluster size, berries per cluster, or berry size. This would indicate that under the conditions of this study, yield was not limited by berry size, but by rather by total berries per vine. Given that total applied water amounts were similar across pre- and postveraison treatments, and yields were higher in treatments receiving less water postveraison, vineyard production and water use efficiency could be optimized by reducing total postveraison water application (relative to total estimated ETc) by up to 75%.

Next steps:
Fruit quality and wine sensory analyses still remain for 2018 samples. Upon completion of analyses, phenology-specific water stress target values will be obtained for all horticultural and agronomic parameters as well as wine sensory characteristics. These will provide winemakers, vineyard managers and irrigators more information upon which to base irrigation management decisions.