EAST LANSING, Mich. — Michigan had a terrible blueberry crop in 2018. Across Michigan, yields for early and mid-season varieties were normal but not great. Yields for late mid-season (Jersey) and late-season varieties (Elliott and others) were terrible. I think this was due to mid-winter cold and several very hot episodes during the growing season.
We had a warm fall in 2017 and did not get cold weather until late November and early December. Early December was cold and snowy. We then had warm weather the week before Christmas with lows above freezing most nights. Temperatures above freezing reduce the plant’s cold hardiness in winter.
We had a very cold episode in the mid-winter around Christmas and New Year’s Eve when temperatures dropped down to zero and below. Some areas dropped down to -20 degrees Fahrenheit. This alternating warm and very cold pattern caused some winter injury in blueberries and other cold tender perennial crops. Some of the blueberry fields looked pretty ratty as the leaves and flowers emerged in the spring of 2018.
After the mid-winter cold, the winter was fairly warm and after a warm February, we expected an early spring. However, March and April were unseasonably cold and wet, which held plant development back. This allowed fruit growers to avoid damage from spring freezes in April. By late April, we were about two weeks behind our normal development.
May was warmer than normal and plants began to move rapidly in the heat. In southwest Michigan, blueberry bloom usually occurs the second week of May. In 2018, the earliest varieties began bloom on May 13. The following week was wet and rainy with only a few good days for pollinating. Many blueberry fields were flooded from heavy rains in April and May with standing water around the bushes.
During the last week of May as the late-season varieties were blooming, we had cool weather followed by a very hot Memorial Day weekend with highs in the mid-90s. I believe this very hot weather as the late blueberry varieties were blooming caused the flowers to age rapidly. Instead of two or three days for the bees to pollinate the open flowers, there was only a day or two before the flower was too old. Normally, blueberries do not bloom all at once. Blueberries set their fruit buds at the tips of the new shoots in late summer and then more flower buds form below the tip as leaf buds in the leaf axils are converted to flower buds. In the spring, bloom begins at the shoot tip and the flowers open sequentially down the shoot. On shoots with good vigor, there may be six or more flower buds each with eight to 12 flowers. Often, the flower cluster at the tip has been pollinated and set fruit before the flowers at the bottom even open. The extreme heat in late May caused bloom to be very rapid and most of the flowers quickly opened in the heat. This means that most of the flowers opened quickly and were only receptive to pollination for a day or two.
The really hot weather also caused the bees to be less active. Because of the extreme heat the bees were only active for a short time. Honey bees stayed in the hive and worked to cool the hive. Wild bees sought cool shelter during the heat of the day.
These two factors really impacted pollination of the late-season varieties. Often, after a blueberry flower is pollinated the petal tube will fall off, and in 2018 we saw the petal tubes hanging on for a long time. Many growers complained of a heavy drop of green fruit. This is an indication that there was poor pollination and seed set in the berries. By June it was obvious we had a very light crop in the late-season blueberries. Often, I saw only a single large berry in a cluster and several very small berries. These small berries never sized.
I have had many calls asking why there was such a poor crop of blueberries. While I think the fluctuating warm and extreme cold had an impact on the plants, I think the main reason for the poor blueberry crop in 2018 was poor pollination conditions with cold, rainy conditions at the beginning of bloom and very hot conditions at the end of bloom.
The estimated total blueberry production in Michigan for 2018 is only 66 million pounds. The 10-year average for Michigan is 98 million pounds. This will be the poorest blueberry crop year since 2005 and 2003 when the crop was 66 and 63 million pounds, respectively. At that time, the blueberry acreage in Michigan was about 17,000 acres. Today, the acreage is over 20,000 acres. I expect the average yields for 2018 to be about 3,500 pounds per acre, much below our average of 5,000 pounds per acre. Almost all this loss is due to a very short crop in the later varieties, which would have harvested in August, September and October. The 2018 harvest ended a month early due to a lack of crop.
See these Michigan State University Extension articles for more information:
— Mark Longstroth, Michigan State University Extension
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