2017 ASHS Annual Conference

Overhead sprinklers are often used to cool blueberry fields in the Pacific Northwest, but more information is needed to determine exactly when cooling is needed. The objective of this study was to identify the critical temperatures for heat damage in northern highbush blueberry (Vaccinium corymbosum L.). An initial study conducted in western Oregon in a mature planting of late-season ‘Elliott’ blueberry revealed that heat damage occurred primarily on sun-exposed berries and happened at both green and blue stages of fruit development. Heat damage was relatively limited in the cultivar (< 3% of the total yield) and generally occurred at air temperatures > 95 °F and berry temperatures > 104 °F. Usually, temperature of the sun-exposed berries was 10–15 °F warmer than ambient air temperature in the field. A subsequent study was conducted to determine whether the critical temperature for heat damage differs between cultivars and green and blue fruit. In this case, a heat-susceptible cultivar, ‘Aurora’, was added to study and compared to ‘Elliott’. Berries from both cultivars were heated using a chamber-free convective unit and exposed to temperatures of 107, 111, 114, and 118 °F for up to 4 hours. Blue fruit had a higher critical temperature and tolerated a longer period of heat exposure than green fruit in both cultivars. However, ‘Aurora’ had a lower critical temperature (green: 107 °F, blue: 114 °F) than ‘Elliott’ (118 °F) and, at the same given temperature, developed heat damage faster and more severely. For example, more than 40% of the green berries were damaged after 3–4 hours at 114–118 °F in ‘Aurora’, while only 20% or less were damaged in ‘Elliott’. Based on these results, blueberry fields should be cooled at air temperatures > 90 °F during early stages of fruit development and > 95 °F during later stages of fruit development.