2017 ASHS Annual Conference

Washington State leads in both total and organic production of highbush blueberry (Vaccinium corymbosum). Production occurs in central and western Washington, which are geographically and climatologically distinct. Western Washington has a maritime climate with wet and mild winters, while central Washington has dry, colder winters with greater risks of winter injury. Growers within both regions implement protective measures to prevent injury due to cold, particularly after bud break and the susceptibility to cold injury increases among emerging vegetative and floral tissues. However, growers lack region- and cultivar-specific resources to guide them on critical temperatures for implementing cold protective measures across key phenological stages. Additionally, information is lacking regarding the most reliable methods for assessing cold hardiness in blueberry. The objectives of this project were twofold: 1) to determine an appropriate and reliable method for assessing cold damage in blueberries and 2) develop cold hardiness curves for blueberry cultivars grown in central and western Washington. Methods evaluated in 2014/2015 were a programmable freezer, glycol bath, and differential thermal analysis, with the programmable freezer and glycol bath being most reliable for cold hardiness determination. Following this, the programmable freezer and glycol bath methods were used to address objective two in central and western Washington, respectively. ‘Duke’, ‘Draper’, ‘Liberty’, and ‘Aurora’ were evaluated in central Washington, while ‘Duke’ and ‘Draper’ were evaluated in western Washington during the 2015/2016 winter. Cold hardiness was measured from late November/early December through April and cold hardiness curves were developed from resultant LT50 (lethal temperature for 50% of floral buds) data. Cold hardiness curves were similar between western and central Washington. Patterns of acclimation and deacclimation were similar for ‘Duke’ and ‘Draper’, while ‘Liberty’ and ‘Aurora’ were more similar to each other. This project is ongoing, but resultant data are being shared with producers and allowing them to better target their cold injury mitigation practices.