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

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.

Possible cold damage to set blueberry fruit
Close up of internal damage to blueberry fruit due to cold temperatures


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

Temperature Damage
30.5°F Slight injury to flowers, little effect on fruit set, occasional necrosis at edges of leaves
28 °F Greater than 2 hours,  40 to 60% loss of fruit set in open flowers and 20 to 30% in closed flowers, unclear if berry weight is affected
26°F Open flowers, after 2 hours, 75% of flowers lost resulting in little fruit set.  After 2 hours, 50% of closed flowers do not open, but if they do open, little effect on fruit set. With increased time, fewer flowers open.
Below 24°F Flowers die, no fruit set, leaves are water soaked and may not recover


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

Location  Cold temperatures 
Waldoboro May 7 below 35F
Warren May 9 below 35 F
Hope May 8 and May 9 below 35F
Liberty weather station down
Searsport weather station down
Ellsworth May 7, 8 below 30.5F; May 9, 10, 11 below 35F
Eastbrook May 7, 8, 9, 11 below 30.5F; May 10 below 35F
Blue hill/ Sedgewick May 7, 9 below 35F
Aurora weather station down
Steuben May 7, 8, 9, 10, 11  below 30.5F
Deblois May 8, 9, 11  below 30.5F; May 10 below 35F
Montegail weather station down
BBHF May 7, 8, 9 below 30.5F; May 11 below 35F
Whiting/E. Machias weather station down
Crawford May 7, 9 below 30.5F; May 8, 10, 11 below 35F