Timing of susceptibility of highbush blueberry cultivars in northwestern Washington to Monilinia vaccinii‐corymbosi, the cause of mummy berry

Abstract

Mummy berry, caused by Monilinia vaccinii‐corymbosi, causes significant yield losses in blueberry fields in the coastal region of the Pacific Northwest, including northwestern Washington (WA). Development of effective disease control strategies are hindered by lack of knowledge of disease epidemiology in this region. This study compared floral and vegetative bud development of four blueberry cultivars, Duke, Bluecrop, Liberty and Draper, by evaluating the timing and number of susceptible buds on plants during the ascospore release period in two counties in northwestern WA in 2015 and 2016. Ascospores were detected from early March until early April in both years. All four cultivars presented susceptible vegetative and floral buds during this period but susceptible floral buds were consistently more numerous and observed earlier than vegetative buds. The timing of peak numbers of susceptible floral buds was earlier in cultivars Bluecrop and Duke compared to Draper and Liberty and peak numbers of susceptible vegetative buds of Bluecrop were observed earlier compared to the other three cultivars. Differences in susceptibility of these cultivars in the field may therefore depend on the timing of ascospore release relative to host development rather than differences in innate susceptibility. The frequency and spatial distribution of primary infections was also examined and seasonal variation was found in the incidence between bud types and no significant association between canopy heights. The outcomes of this research will be used to develop targeted and effective methods to prevent primary mummy berry infections in WA.