West central Michigan weather conditions for the past two weeks have been typical of late summer—daily maximum temperatures averaging 80 degrees Fahrenheit and minimum temperatures averaging 60 F. In addition, there was an end for the summer drought that affected the small fruit industry during July and August. Rains during the last week of August were abundant, producing between 3.5 and 4 inches of rain distributed over a period of seven days. Another 2.5 inches have accumulated during the first days of September. These weather conditions favored fruit quality for all berries harvested at the end of August.

Blueberry harvest in west central Michigan is still underway at some late season fields. Reaming amounts of late season berries are expected to be completely harvested by mid-September. Crop remnants are machine harvested and laborers are moving out of the state or to another fruit crop, such as apples.

On the other hand, fall raspberries, the second largest small fruit crop in west central Michigan, continue producing fruit of very good quality without major disease or insect problems.

As the blueberry harvest comes to an end, in 2018 there were a series of environmental problems affecting blueberry production causing a substantial decrease in the expected crop volume. According to some packers and shippers, and based on the numbers reported so far by the USDA, Michigan’s crop volume for 2018 is between 35 and 40 percent lower than the expected volume. In contrast to other seasons when insect pest problems associated with spotted wing Drosophila were the main reason behind crop loses, the main problems in 2018 were weather related—winter damage and weather adverse pollination conditions.

Early in the season we were able to document the impact on blueberries of subzero temperatures in the middle of winter followed by unseasonal warm temperatures. By the end of December 2017, most blueberry varieties were close to completing the chilling requirements, and they were already at or beginning the resting stage. However, on Jan. 4 and 5, temperatures dropped to –1.0 and -9.8 F, respectively. Those subzero temperatures were followed by a warming up period of six days when daily temperatures raised up steadily reaching 58–59 between Jan. 10 and 11.

A second warming up of daily temperatures occurred between Jan. 20 and 26. During those days, daily temperatures raised up to 53–54 F, respectively. These sudden increments on daily temperatures potentially terminated the resting period in early season varieties, exposing them to frost/freeze damage by subsequent return of winter temperatures.

A similar situation occurred days later on Feb. 12–13. During those days, minimum temperatures dropped to -1.0 and 1.0 F, respectively. Again, these subzero or close to zero temperatures were followed up by days when daily maximum temperatures reached up to 63 F. Such temperatures were observed on Feb. 19 and 20.

By the beginning of the bloom period, many leaf and flower buds were already damaged or dead because of this weather pattern occurring during blueberry plant’s resting stage. Entire fields of all varieties exposed to those sudden fluctuations of temperatures during the resting period were not able to produce fruit at all. Leaf buds were winter killed and flower buds that opened aborted.

A second weather-related problem was pollination. Blueberries are plants originated in northern regions of North America characterized by cloudy days and cooler temperatures during the bloom period. In 2018, blueberry pollination took place under weather conditions characterized by low humidity, and relative high daily maximum temperatures. For example only 4 inches of rain accumulated between May 20 and June 27 in west central Michigan, and daily maximum temperatures reached up to 90–92 F during the pollination period of most varieties.

It has been documented by Kelly, et al. (2010) that heat stress in most plants causes pollen sterility when flowering plants are exposed for short periods of time to temperatures above 25–26 degrees Celsius (77–78 F). These problems with low pollination associated with adverse weather conditions were reported by growers very early. By the middle of summer, they were observing a very light crop in most fields.

In summary, the resulting short harvest season and small crop observed in 2018 were the result of weather associated conditions. For the past five years, those climate change-related conditions have been the main factor behind changes in Michigan’s blueberry productivity. Those weather patterns are becoming a recurrent issue requiring a more in-depth study to present alternatives to deal with the impact of climate change in our blueberry production system.