West central Michigan small fruit update – May 4, 2021

Blueberries are blooming in west central Michigan and freeze/frost events from past days seem not to have a significant effect on crop conditions.

Bluetta blueberry bush with no damage to flower buds.
Early blueberry variety Bluetta with no damage to flower buds after the April 21-22, 2021, freeze/frost events. Photo by Carlos García-Salazar, MSU Extension.

West central Michigan has remained under unseasonal cold and windy conditions over the past seven days. Minimum and maximum daily temperatures averaged only 45 and 68 degrees Fahrenheit, respectively. Although these temperatures are below average temperatures for this time of year, they allowed for a substantial accumulation of growing degree days (GDD), enough to advance the bloom period of blueberries and strawberries. In the southern part of Allegan County, the GDD accumulation terminated the diapause on cherry fruitworm and cranberry fruitworm. Overwintering adults of these fruitworms started showing up on pheromone bated traps around Fennville, Michigan, and in southwest blueberry fields (see table).

Regarding precipitation, west central Michigan remains under moderated drought conditions. During the past seven days only, scattered showers deposited less than 0.25 inches in the area. These drought conditions are occurring at the time when water demand by blueberries and strawberries is critical. Water deficit during the bloom period affect fruit set and berry size in both berry crops. To mitigate this problem, provide supplemental irrigation for blueberries and strawberries.

As of May 4, blueberries started blooming in Allegan County around the Pullman-Grand Junction, Michigan, area and in southern counties. This week, we conducted a new inspection in blueberry fields at the Covert-Grand Junction and Fennville areas and around West Olive, Michigan, in Ottawa County. The purpose of this inspection was to continuing assessing the effects of freeze/frost events occurring around April 21 -22 when nightly temperatures dropped below the freezing point around Michigan’s blueberry growing region.

Our previous evaluation conducted right after these events indicated a light damage to blueberry fields inland away from the lakeshores. However, the damage was not widespread. Only some fields with the varieties Wayman and Bluecrop suffered some damage at fruit buds already in the late pink stage of development. Flower buds in earlier stages of development were not affected or only slightly affected.

Currently, most varieties are in pink to late pink bloom stages in counties north of Allegan County. Early varieties like Wayman, Bluetta, Bluecrop and Duke are at 5 to 50% bloom in and around the Pullman-Grand Junction area in Van Buren County (see photo).

Regarding insect pests of blueberries, cranberry fruitworm and cherry fruitworm started emerging from their overwintering sites in Allegan and Van Buren counties. Early detections of both species have been reported around the Fennville-Grand Junction area and in Van Buren County. Fruitworm pheromone traps should already be deployed to detect the early arrival of fruitworm adults and prevent fruitworm damage.

We also recommend visiting Michigan State University Enviroweather to check the phenology models for timing the insecticide applications against these pests. The table below shows the current GDD base 50 F accumulated so far at three areas in west central Michigan. These table is only a guide for planning your fruitworm integrated pest management. Use moth captures in your pheromone traps for biofixing the degree day accumulation as recommended by the Enviroweather phenology models.

Cranberry fruitworm and cherry fruitworm phenology stages important for timing the beginning of insecticide applications at three different locations in west central Michigan. GDD accumulation for first adults and first eggs are calculated after the biofix. (Biofix = date after moths are continuously caught in the pheromone trap.)


First adults

First eggs

Current GDD accumulation as of May 4, 2021

Grand Junction


West Olive

Cherry fruitworm

238 ± 30

432 ± 15




Cranberry fruitworm

375 ± 20

460 ± 20




*Adults already emerging around Grand Junction area.

If you have questions regarding using the cranberry and cherry fruitworm phenology model, call your local MSU Extension office for assistance. You may also contact me at 616-260-0671 or garcias4@msu.edu.

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