Cooperative Extension: Maine Wild Blueberries

End of chance of Monilinia infection and recent cold temperatures, May 11, 2022

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Mummy berry season

Cups have dried up in plots in the midcoast and downeast with the warm, dry weather we are having.  If you have a late field, you may still have mummy berry cups.   What will start to show up this week and next are symptoms of mummy berry which include dead and dying leaves and flowers with grey masses of spores at the base of the tissue.   It is too late to spray most fields to control mummy berry at this point.

Cold Temperatures

These past few days we have been having cold temperatures overnight down to the thirties F and sometimes into the twenties F.  These temperatures can damage open flowers and fruit set if they last long enough.  Typically temperatures need to be below 31°F to see any damage to the plants, but this will vary by clone.   At some of our weather stations, we have recorded temperatures below 35°F and below 31°F (some areas in the field may be lower) since Saturday May 7th.  Whether there was any damage to your plants will depend upon how open your flowers were, how cold it got in different areas of the field (such as hollows and lower parts of hills), and how sensitive your plants are to cold.  You can check for cold damage to set fruit by cutting open the fruit and looking for brown, damaged areas in the fruit.

Temperature effects on wild blueberry flowers and leaves according to Hall et al. 1971, Hall and Hildebrand, 1988, and Hicklenton et al., 2002.  

Cold temperatures in field with weather stations from May 7 to May 11.