Please FRET: Vineyard Irrigation Scheduling Using Forecasted Reference ET

Commodities

• Fruits: grapes

Practices

• Crop Production: drought tolerance, irrigation, water management

Efficient and well-timed irrigation is fundamental to sustaining vineyard productivity, fruit quality, and water-use efficiency in the increasingly variable weather of the western United States. Standard irrigation scheduling relies on cumulative reference evapotranspiration (ET) to estimate crop water use. Although widely implemented, this "backfilling" method cannot anticipate rapid weather changes - particularly heat events - that increase atmospheric demand beyond recent conditions. These mismatches can lead to preventable water stress, wasted pumping costs, and reduced fruit quality.

Forecast Reference ET (FRET), a new National Weather Service product, provides short-term ET forecasts that may better align irrigation timing with future evaporative demand. FRET is publicly available and easy to access, but it has not been evaluated in commercial vineyards, and growers currently lack guidance on whether and how to use it. Wine grapes are well suited for this evaluation because irrigation is already managed efficiently and water stress strongly influences berry development and wine quality.

This project will compare standard ET and FRET-based scheduling at two irrigation rates (100% and 50%) across three commercial Oregon vineyards over two seasons. We will quantify effects on vine water status, growth, and fruit composition to determine whether forecast-based irrigation improves timing, reduces stress, and maintains or enhances fruit quality.

Through targeted Extension programming statewide, we will provide practical recommendations for incorporating FRET into irrigation decision-making. By evaluating a no-cost irrigation support tool under real operating conditions, this project directly supports regional sustainability, water efficiency, and producer resilience.

1. Implement and compare irrigation scheduling method at commercial vineyard sites. Establish side-by-side irrigation treatments using Forecasted Reference Evapotranspiration (FRET) with standard Reference Evapotranspiration (ETo) at two irrigation rates (100% and 50%) at three vineyard sites in western Oregon over two years.
2. Evaluate applied water, vine growth, water stress physiology, and fruit quality responses to irrigation scheduling method and rate. Measure the effects of FRET vs. ET-based irrigation schedules and application rate on applied water amounts, vine vegetative growth, stem water potential, leaf gas exchange, and fruit chemistry at each vineyard site over two years to determine how forecast-based irrigation influences vine performance and crop quality.
3. Increase producers knowledge and capacity to use FRET for irrigation scheduling. Deliver at least four regional and statewide Extension programs that introduce FRET-based irrigation scheduling, present project results, and provide practical guidance for integrating FRET into commercial vineyard irrigation management.