Location: Horticultural Crops Research UnitTitle: Thermal cooling with sprinklers or microsprinklers reduces heat damage and improves fruit quality in northern highbush blueberry
|YANG, FAN-HSUAN - Oregon State University|
|STRIK, BERNADINE - Oregon State University|
|ZHAO, YANYUN - Oregon State University|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2020
Publication Date: 8/1/2020
Citation: Yang, F., Bryla, D.R., Orr, S.T., Strik, B.C., Zhao, Y. 2020. Thermal cooling with sprinklers or microsprinklers reduces heat damage and improves fruit quality in northern highbush blueberry. HortScience. 55(8):1365-1371. https://doi.org/10.21273/HORTSCI15119-20.
Interpretive Summary: Hot and sunny weather is a persistent threat to blueberry production in the Pacific Northwest and elsewhere in the country, causing damage and softening in the berries. When damage occurs, those berries are unmarketable, particularly in the fresh market. Fruit softening also reduces the marketability of the berries and shortens the shelf life. In some case, growers use sprinklers to irrigate blueberries, and these sprinklers can be used to cool the fruit. However, many new plantings are irrigated by drip, so growers are seeking alternative systems to protect the fruit from summer heat. Adding overhead micro-sprinklers to existing drip-irrigated fields is one option. Using micro-sprinklers to mitigate high temperatures has been found to be effective in other horticultural crops, including apples and grapes. No prior research exists that has examined whether cooling with sprinklers or microsprinklers can improve fruit quality or alter harvest date in highbush blueberry. Therefore, the objective of the present study was to evaluate the efficacy of using over-canopy sprinklers and micro-sprinkler systems to reduce berry temperature, prevent heat damage, and improve fruit quality in blueberries. Cooling with over-canopy sprinklers or micro-sprinklers was very effective for reducing berry temperature during warm weather events. In addition to protecting the berries from heat damage, in some cases, cooling increased berry weight and berry firmness. Turning micro-sprinklers on-and-off in 20-minute cycles was generally as effective as continuous cooling, but it used 50% less water and resulted in lower relative humidity during and after cooling. Less humidity after cooling improves fruit harvest (drier berries in the morning) and reduces potential problems from fungal diseases and slugs.
Technical Abstract: The objective of the present study was to evaluate the efficacy of using over-canopy sprinklers and micro-sprinkler systems to reduce berry temperature, prevent heat damage, and improve fruit quality in northern highbush blueberry. The trials were conducted in western Oregon. To test sprinklers, four treatments were assigned for 2 years to an existing field of ‘Elliott’ blueberry, including two controls with no cooling that were irrigated by drip or sprinklers (at night only) and two cooling treatments that were both irrigated (night) and cooled (day) by the sprinklers. Cooling with sprinklers was run for 15 min every hour when air temperature was > 32 or 35 C. Berry temperature dropped quickly with each irrigation pulse and remained well below the temperature of the non-cooled berries throughout the cooling period. As a result, berry damage was reduced to nearly 0% with cooling, and berry weight was increased by as much as 35%. Delaying the process until 35 C resulted in only slightly higher berry temperatures but reduced irrigation water use by 3.0-3.4 million liters per hectare each year. With micro-sprinklers, cooling was tested at both a commercial farm and an experimental site. At the farm, 5-ha blocks of ‘Aurora’ blueberry either had no cooling or were cooled using micro-sprinklers run continuously or pulsed in 1-h or 20-min cycles during extreme heat events (> 35 C). Continuous cooling was the most effective treatment for reducing temperature of the berries but resulted in wetter conditions afterwards. Pulsed cooling, especially with short cycles, effectively maintained fruit temperatures near that of ambient air and reduced water use by 50%. At the experimental site, cooling with micro-sprinklers in 20 min cycles reduced heat damage in both ‘Elliott’ and ‘Aurora’ and increased weight and firmness of the berries in the latter. Overall, pulsed cooling with either sprinklers or micro-sprinklers was very effective for reducing berry temperature and improving fruit quality in northern highbush blueberry.