Develop a Risk Assessment Model to Help Manage SWD in Michigan Tart Cherries

Project goal:  To provide a degree-day risk model for growers to help them decide when to begin SWD control based on cherry fruit phenology.

Project description: We have evaluated different phenological stages of tart cherry fruit throughout the growing season to determine if there is a stage of ripeness that triggers SWD oviposition.  In 2018 and 2019, we tested fruit for differences in color, firmness, penetration force, brix, and size.  We collected fruit every two days from mid-June through harvest and assessed the cherries for the aforementioned qualities.  These fruits were placed into no-choice bioassays to determine which phenological stage(s) of fruit are susceptible to SWD.  Our analyses have shown that color is a significant factor in initiating SWD oviposition, and color is most correlated with SWD infestation.  As fruit turns from green to red, the green:red ratio is directly related to when SWD infest fruit, and we used the established Zavalloni phenology model to correlate infestation to growing degree days for Montmorency tart cherry development.  We found that in a no-choice bioassay, SWD do not infest fruit at ~530GDD base 4C, even when given ‘no-choice’.  These preliminary data are currently the only method to predict fruit infestation based on a quantifiable stage of crop development and from this data we have produced a prototype SWD risk model.

In 2020, we attempted to verify the prototype SWD risk model in three tart cherry growing regions in Michigan and also improve our understanding of how temperature and relative humidity play a role in rapid SWD population increases and infestation of managed fruit.  To verify the model, we monitored adult SWD at three sites in the three cherry growing regions of the state.  Each location had five pheromone baited deli cup traps that were checked every Monday, Wednesday, and Friday from beginning of June through harvest.  We also collected 250 fruit from each site every M,W,F for larvae sampling.  One temperature and relative humidity datalogger was placed at each site.  To improve our understanding of how temperature and relative humidity play a role in rapid SWD population increases we placed five SWD traps at NWMHRC, TNRC, and SWMREC.  Traps were checked daily from beginning June through harvest.  One hundred fifty fruit per tree was also collected daily and checked for the number of larvae.  Each trap tree contained a temp and RH datalogger.  We will compare trap count data and infestation data with information collected from the dataloggers to understand if daily fluctuations of temperature and relative humidity influence SWD activity.

Results: Using Fruit Phenology to Determine Risk of SWD Infestation 2019

Project lead/collaborators: Nikki Rothwell, Emily Pochubay, Todd Einhorn, and Larry Gut

Funding sources:  Project GREEEN and Michigan Cherry Committee

Start year: 2018

End year: 2020