West central Michigan small fruit update – May 16, 2017

Carlos Garcia-Salazar<garcias4@msu.edu>, Michigan State University Extension - May 16, 2017

Spring frosts caused limited damage to berry crops in west central Michigan, but the full impact still is under evaluation.

Jersey variety, style and ovary damaged in West Olive, Michigan. Photo by Carlos Garcia-Salazar, MSU Extension.

Weather conditions in west central Michigan had a sudden turn for the worst during the past week, causing limited frost damage to berry crops, mainly blueberries and, to some extent, strawberries. The unexpected spring frosts that occured May 8 and 9, 2017, had some significant impact on blueberry varieties that were in advanced bloom stage, for example late pink bud and early bloom (25-50 percent bloom). Those bloom stages are less tolerant to freezing temperatures than early stages.

According to “A Pocket Guide to IPM Scouting in Highbush Blueberries,” Michigan State University Extension bulletin E2928, the late pink bud stage can tolerate freezing temperatures of 24 to 27 degrees Fahrenheit. However, the early bloom and full bloom stages tolerate only temperatures of 25 to 28 F.

During May 8 and 9, temperatures dropped down to 22 F in most blueberry fields across west and southwest Michigan. The length of the freeze/frost events was three to seven hours, depending on the location. Blueberry fields located in southern Allegan and Van Buren counties that were in advanced bloom stages, late pink to early bloom were the most affected. This included early-season varieties like Bluetta, Duke and others. Conversely, varieties like Jersey and Elliott, and other late-season varieties that were still at early pink stage, suffered significantly less damage.

A frost damage evaluation conducted immediately after the last event, May 9, in unprotected fields at Allegan, Van Buren and Ottawa counties showed the following percentages of flowers and buds damaged:

Allegan and Van Buren counties

Elliott = 14 percent
Jersey = 44 percent
Bluecrop = 53 percent

Ottawa County

Elliott = 6 percent
Jersey = 33 percent
Bluecrop = 34 percent

Although no substantial damage occurred at fields with Elliott or Jersey, there is a potential pollination problem later on since some flower structures inside unopened buds may have been affected (see picture). Some late pink buds that were dissected and examined with a dissection microscope revealed some stamens and the style were damaged.

Regardless of the variety or location, spring frost damage was not significant in blueberry fields that were frost protected. Also, since only a portion of the first bloom was affected, it is expected that the spring frost damage to blueberry production may not be significant.

Early-season blueberry insect problems

Cherry fruitworm and cranberry fruitworm have been emerging at Allegan and Van Buren County fields.

Below is a table with the predicted degree-days when we are expecting the emergence of cherry fruitworm and cranberry fruitworm, and the current degree-day accumulation for key weather stations in west Michigan.

Predicted degree-days for cherry fruitworm and cranberry fruitworm emergence
Insect	First adults	First eggs	Current degree-day accumulation (5/2/2017)
Insect	First adults	First eggs	Grand Junction	Fennville	West Olive
Cherry fruitworm	238 ± 30	432 ± 15	330*	276	244
Cranberry fruitworm	375 ± 20	460 ± 20	330	276*	244

* Adults already started emerging around Fennville and Grand Junction area.

This article was published by Michigan State University Extension. For more information, visit https://extension.msu.edu. To have a digest of information delivered straight to your email inbox, visit https://extension.msu.edu/newsletters. To contact an expert in your area, visit https://extension.msu.edu/experts, or call 888-MSUE4MI (888-678-3464).