West central Michigan small fruit update – May 9, 2017

The region has seen several days with temperatures dropping to the low 30s, causing significant damage to small fruit crops, mainly blueberries and strawberries.

Until Sunday, May 7, 2017, temperatures in west central Michigan remained cold but well-above the freezing point. This drop in daily temperatures gave some pause to small fruit growers that were concerned with the rapid plant growth and development resulting from high temperatures during early spring. Although there were some localized freeze/frost events affecting some strawberry fields, no major problems were reported for other crops like blueberries. However, during the early hours of Monday, May 8, and Tuesday, May 9, temperatures dropped below the freezing point, substantially damaging blueberries and other small fruit crops.

The first important freeze/frost event of May 8 lasted from around 3 a.m. to 7 a.m., and temperatures dropped as low as 28 degrees Fahrenheit. However, some strawberry and blueberry growers reported temperatures of up to 22 F. The second event on May 9 affected mainly counties north of Van Buren County. This event lasted from 2 a.m. to 7 a.m. and temperatures dropped below the freezing point, 30-31 F.

This sudden change in the current weather conditions was unexpected because overcast conditions of the previous days did not signal a potential risk of spring frosts. Growers with overhead irrigation have been able to avoid significant crop losses by turning on the sprinkle irrigation system in some of the at-risk blueberry fields. Unfortunately, some growers did not have enough water to protect their fields and ran out of water before the freeze/frost was over. This may have increased the frost damage considerably.

A preliminary evaluation of the damage to blueberries at Ottawa, Allegan and Van Buren counties showed that most damage occurred in Van Buren County and in the southern part of Allegan County. Most affected fields were those with early varieties like Brigitta, Duke and Bluecrop that were left unprotected. In Brigitta, for example, 100 percent of the flowers were damaged. In Bluecrop, the first bloom and all flowers that were already open were also damaged. Blossoms that were in late pink stage or at earlier stage were not damaged.

In Ottawa County and north Allegan County, the damage is less significant. The blueberry bloom period was one week behind that of Allegan or Van Buren County. Thus, fewer flowers were already opened. However, in comparison to Van Buren County and other southern counties, counties north of Allegan County sustained two continuous days of freezing temperatures. This may increase the damage caused by spring frosts. A more complete evaluation will be conducted once field conditions allow.

Blueberry disease management

As a result of the frost damage affecting most blueberry fields during the past 48 hours, special care should be taken to protect plants from disease infections. There is a potential risk for infections caused by mummyberry and Phomopsis twig and shoot blight, as well as Pseudomonas syringe infections. Michigan State University Extension suggests applying preventative fungicides as soon as weather and soil conditions allow.

Mummyberry preventive applications are recommended with Indar, Orbit, Quilt Xcel, Prolin and Ziram, among others. Indar, Tilt and Quilt Xcel have a 30-day pre-harvest interval (PHI). Do not make more than two consecutive applications of Quilt Xcel before switching to a fungicide with a different mode of action (please consult MSU Extension bulletin E0154, “2017 Michigan Fruit Management Guide,” for more fungicide options and recommendations). If your fields presented problems with Botrytis twig blight in the past, Ziram will be effective against mummyberry and Botrytis.

Early-season blueberry insect problems

Cherry fruitworm and cranberry fruitworm have been emerging in 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


First adults

First eggs

Current degree-day accumulation (5/2/2017)

Grand Junction


West Olive

Cherry fruitworm

238 ± 30

432 ± 15





Cranberry fruitworm

375 ± 20

460 ± 20




* Adults already started emerging around the Grand Junction area.

Upcoming meetings

The Blueberry Pre-bloom Twilight Meeting is May 11, 2017, from 5:30 to 7 p.m. at the Ottawa County Fillmore Complex Board Room, 12220 Fillmore Street, West Olive, MI 49460. Farm Services Agency representatives will briefly update growers on loans and services available for small fruit growers. For a complete description of the agenda and to register, go to Blueberry Pre-bloom Twilight Meeting.

There is no cost for attending this meeting, which is open to all people. However, we would appreciate if you preregister online so we have a count of participants to provide refreshments and handouts. Reister's Grower Services, LLC, is sponsoring our meeting and they will provide a light diner, pizza and refreshments.

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