ASHS 2025 Conference

Extreme heat events threaten raspberry (Rubus ideaus) production in the U.S. Pacific Northwest. The aim of this study was to evaluate strategies for reducing heat stress at a field site located in Prosser, Washington. Treatments were arranged in a split-plot design with four replicates and included three heat mitigation treatments (evaporative cooling with micro-sprinklers, shade cloth, and an untreated control) as main plots and four genotypes (‘Meeker’, ‘WakeField’, WSU 2188, and ORUS 4715-2) as subplots. Across the genotypes, evaporative cooling and shade cloth enhanced photosynthesis and chlorophyll fluorescence and increased yield compared to untreated controls. Shade cloth also resulted in higher stem water potentials than the other mitigation treatments, indicating improved hydration in each genotype. Preliminary economic analyses indicate that shade cloth is more expensive to install than micro-sprinklers for cooling and may interfere with mechanical operations. Evaporative cooling, on the other hand, increases weed pressure, which requires additional management. It also increased postharvest pathogens on the fruit after two weeks of cold storage in ORUS 4715-2. In each case, cooling was run continuously whenever ambient air temperature was > 30°C. Next, we will evaluate whether cooling for 15 minutes every hour is effective and results in fewer weeds and pathogens than continuous cooling.