Dr. Harald Scherm has determined the mummy berry potential (germination and development of the apothecia); all southern Georgia blueberries that are showing either green tip or early bloom developmental stages are at high risk for mummy berry infection at this time and going forward. This is especially true as temperatures warm up next week and we have rainfall. If we can extrapolate the temperature information from Dr. Annemiek Schilder’s Michigan fact sheet on mummy berry (Schilder et al., 2008) to rabbiteyes, we do start to see a match again this year:
“Ascospore germination requires free water, and the optimum temperature for infection of susceptible tissue is 57°F. Developing vegetative buds become susceptible to infection when about 1/6th inch of green tissue is exposed. Flower buds become susceptible when the bud scales begin to separate. At 57°C with adequate moisture, germination and infection can occur within 4 hours; at 36°F, at least 10 hours of leaf wetness are required for infection. Blight symptoms appear about two weeks after infection. In lowbush blueberries, developing leaf and flower bud tissues are more susceptible to infection after exposure to freezing temperatures, and this susceptibility can last for up to 4 days after the frost event. This also appears to be the case in highbush blueberries.”
Mummy berry is very well tied to the initiation of budbreak and bloom, especially in rabbiteyes. With rabbiteye green tip and/or bloom development likely starting next week, producers need to be ready to spray mummy berry active fungicides in earnest.