Cold temperatures the past week in some blueberry areas
Cold temperatures that would cause damage to flowers and pinheads occurred in Aurora area and possibly in Hope and in the barrens. In the Hope area on May 31st, temperatures were close to 30F for about 1 hour. In the barrens, temperatures were about 28F for about 1 hr in the early morning of May 31st and June 1st. The coldest conditions were at our weather station in an Aurora field. There were cold temperatures below 28F on: May 30th – below 28F about 20 minutes and cold about 1 hr; May 31st – 2 hours below 28F and lowest temperature was about 22F for 1.5 hr; June 1st – temperature were below 28F for about 7 hours and coldest temperatures were around 22F for 2 hours; June 2nd about 1 hour below 28F and lowest temperature was 26F.
Cold temperature damage
Cold temperatures can damage flowers visibly by browning the flower (picture), but also internally. Internal damage may not appear until after fruit set when a lack of fruit development is observed. You can check the green fruit in your field for cold damage by cutting fruit open. Undamaged berries will be green inside, while damaged berries will be brown inside. Damage will vary depending on local conditions in your field and the stage that the wild blueberry plants were in when cold temperatures occurred. Typically, lower sections of fields experience more cold damage than higher points. According to research conducted in Nova Scotia, wild blueberry flowers and leaves have the following effects from exposure to cold temperatures. Open flowers are more susceptible to freezing damage than closed flowers. Freezing temperatures can also affect whether or not closed flowers will open. The colder temperatures are, the more likely it is that fruit set will be damaged, regardless of the length of time that it is cold.
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 |
