FIELD OBSERVATIONS OF ASCOSPORE DISCHARGE OF MONILINIA VACCINII-CORYMBOSI IN NORTHERN HIGHBUSH BLUEBERRIES
Gina Dabbah1, Annemiek Schilder2, Timothy Miles1.
1California State University Monterey Bay, Seaside, CA, 2Center for Integrated Plant Systems, Michigan State University, East Lansing, MI.
Monilinia vaccinii-corymbosi (Mvc) is the causal agent of mummy berry, a potentially devastating fungal disease in North American highbush blueberries (Vaccinium corymbosum L.). M. vaccinii-corymbosi, can account for more than an 80% reduction in crop yield. To improve disease management practices, we quantified the environmental variables that impacted levels of ascospore discharge. A Burkard spore trap was used to collect ascospores within blueberry fields near Grand Junction and Nunica, Michigan in the springs of 2002, 2003, 2004, and 2009. The spore trap measured airborne ascospores on an hourly and daily basis. Weather data including relative humidity, soil moisture, and air temperature, were also collected from Michigan State University’s Enviroweather network. A previously developed degree-day model from another region was also assessed to compare amount of chill-hours (hours < 7.2 ˚C) needed for wintering and degree-days (days > 7.2 ˚C) acquired. We found ascospore discharge was inversely related to daily relative humidity. The majority of ascospores were discharged after 60 - 80 growing degree-days and after 3,000 chill-hours were attained. Peak ascospore discharge occurred when apothecia cup sizes reached 6 mm. The results from this study may be used to better predict the timing of ascospore discharge in order to optimize fungicide application timing.