Fruit Zone Cooling in Winegrapes During Heatwaves
Ben-Min Chang, James Harbertson, and Markus
Keller*
*Washington State University, 24106 N. Bunn Rd., Prosser, WA,
99350 (mkeller@wsu.edu)
Heatwaves impose excessive heat stress on grapevines and may compromise grape production. Knowing how vines respond to elevated temperature can inform management decisions. We acclimated potted Cabernet Sauvignon vines to warm (32°C/15°C day/night) or cool (27°C/10°C) seasons before exposing them to a spectrum (40 to 25°C) of maximum temperature regimes in environmentally controlled growth chambers. Leaf gas exchange was measured at noon and in the late afternoon, when air temperature reached its maximum. The results showed that the vines responded to elevated air temperature with a reduction in gas exchange. The sensitivity of leaves to temperature change was similar in vines acclimated to warm and cool seasons, suggesting that mitigating sudden raises in temperature might be the key to prevent heat stress. To mitigate heat stress in the vineyard, we developed a misting-type evaporative cooling system (MECS). The MECS detects leaf or fruit surface temperature and automatically activates misting nozzles at 35°C, but stops misting if the surface temperature is lower than 33°C. Following operation for canopy cooling of Cabernet Sauvignon in 2020, we modified the MECS in 2021 to mitigate heat accumulation in the fruit zone, using upward-facing nozzles placed on the drip-irrigation wire. Successive heatwaves in 2021 brought record high air temperatures of >44°C in late June, during the period of berry size determination. The MECS kept the air temperature in the fruit zone 7°C cooler than the peak ambient temperature. Cooling the fruit zone during heatwaves resulted in larger berries, heavier seeds, and more seeds per berry. Titratable acidity was higher in the juice from cooled vines. There was no significant effect of the cooling treatment on yield, disease incidence, berry splitting, sunburn, or shoot growth. These results show that the MECS can stabilize grape berry growth and acidity during extreme heatwaves.
Funding Support: Northwest Center for Small Fruit Research Program, USDA Specialty Crop Block Grant Program, Washington State Grape and Wine Research Program
