As heat waves become more common, researchers at Washington State University are studying ways to protect raspberry crops from extreme temperatures. A two-year study found that both 40% shade cloth and overhead micro sprinkler cooling reduced heat stress and improved yields, but shade cloth provided the greatest overall economic benefit.
Key Findings
- Extreme heat damages fruit. During a July heat wave, untreated raspberries often reached temperatures more than 10°F hotter than the surrounding air, increasing the risk of heat damage.
- Both cooling methods worked. Shade cloth consistently kept berry temperatures close to ambient air temperature, while overhead cooling was effective when irrigation water was available.
- Shade cloth produced higher yields. Both methods increased production compared to untreated plants, but shade cloth slightly outperformed overhead cooling in the second year, especially when water restrictions limited sprinkler use.
- Fruit quality remained good. Neither treatment significantly affected fruit quality, although overhead cooling increased postharvest mold in some varieties because of the added moisture.
- Shade cloth generated the best financial return. Although installation costs are higher, increased yields produced the strongest economic benefit.
- Water availability is becoming a critical issue. As irrigation restrictions become more common, shade cloth may become a more reliable heat mitigation strategy than evaporative cooling.
Looking Ahead
Researchers are now developing sensor-controlled "smart" cooling systems that activate sprinklers only when needed, reducing water use while protecting fruit. Plant breeders are also working to develop raspberry varieties with improved heat tolerance.
Why This Matters for Growers
With hotter summers becoming more common, growers should begin evaluating long-term heat mitigation strategies. While overhead cooling remains a viable option where water is plentiful, shade cloth appears to offer the best combination of improved yields, profitability, and resilience under future climate conditions.
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Made in the Shade: Protecting Raspberries From Extreme Heat