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Estimating the Risk of Mummy Berry Infection of Your Blueberries With Knowledge of the Local Environment, Host Susceptibility and Mushroom Development

Volume 5 Issue 10

Dalphy Harteveld, Postdoctoral Researcher in Plant Pathology, Dr. Peever’s Program

The presentation of Dr. Harteveld focused on estimating the early season infection risk of mummy berry of blueberry. The three major components that influence infection risk are: 1) a virulent pathogen, 2) a conducive environment and 3) a susceptible host. These components were investigated in diseased fields in Whatcom and Skagit Counties during the 2015-16 and 2016-17 production seasons. Ascospore release by the pathogen was observed from early March to mid-April and averaged 35 days over the two years. Environmental factors and their thresholds conducive to apothecia development and longevity included soil temperature and air temperature at daily averages of 50 °F, ~ 40% soil moisture, and solar radiation at 12 MJ/m2. WSU Agweathernet stations within ~2 miles of infected blueberry fields will be a useful tool to monitor environmental factors, however these stations currently do not record soil moisture data. Host susceptibility was investigated for four cultivars, Bluecrop, Draper, Duke and Liberty, with 3 fields of each cultivar in each of Whatcom and Skagit Counties. Previous research has demonstrated that blueberry is susceptible to infection by ascospores at bud burst and tight cluster stages of flower buds and when >1/4” green tissue is visible on leaf buds. In our research, a larger number of susceptible flower buds was observed on all cultivars compared to leaf buds during the ascospore release period. Therefore, it appears that monitoring early stages of flower development may be more important than monitoring leaf buds in the PNW. Variation in disease levels among cultivars may be related to differences in the timing of bud break and early flower and leaf development. Bluecrop and Draper had the largest numbers of susceptible flower buds approximately 2 weeks earlier than Liberty and Draper and Bluecrop had largest numbers of susceptible leaf buds 3 weeks earlier compared to the other cultivars. These differences in timing of bud break relative to the ascospore release window may result in different levels of disease on the different cultivars due to disease escape rather than to innate differences in susceptibility.