West central Michigan small fruit update – May 2, 2017

Wet and cold weather is delaying growth and development in most small fruit crops, and is conducive for fungal infections during blueberry bloom.


After a period of relatively good weather conditions that pushed small fruit growth and development to an early beginning, we are passing through a period of wet and cold weather that is halting plant growth. For the past seven days, temperatures returned to conditions more typical of Michigan’s early spring. Minimum temperatures during this period averaged 47 degree Fahrenheit and maximum temperatures averaged 65 F. On average, daily temperatures were around 56 F.

In addition, there has been some precipitation during most of the past week, leaving between 2 and 2.5 inches of rain in the area and contributing to a total accumulation of 12 to 15 inches of rain since Jan. 1.

Low temperatures have slowed down the degree-day (DD) accumulation with more significant impact in counties north of Allegan County. So far, there are 172 DD base 50 accumulated around Ottawa County and 228 DD at Grand Junction in Van Buren County.

Blueberry disease problems

Blueberries in west central Michigan are at different bloom stages, going from late pink bud to 25 percent bloom. Although no spring frosts have been reported, there is a potential risk of isolated freeze/frost events that may create the conditions for fungal infections such as mummy berry and phomopsis twig and shoot blight. However, the rain from the past seven days left blueberry fields with standing water that is preventing growers from entering the field to apply the recommended fungicide treatments.

Michigan State University Extension suggest that as soon as weather and soil conditions allow, growers need to apply fungicides to prevent mummy berry shoot strike, phomopsis twig blight, anthracnose and botrytis twig blight infections.

Mummy berry 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 mummy berry and botrytis.

Early-season blueberry insect problems

Cherry fruitworm and cranberry fruitworm are emerging in Allegan and Van Buren County fields. The cherry fruitworm emergence is showing up as predicted by our degree-day model.

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


432 ± 15




Cranberry fruitworm






*Adults already started emerging around the Grand Junction area.

Accordingly, pheromone traps should already be deployed (175-200 DD accumulated since March 1). Traps should be inspected twice a week to estimate with accuracy the biofix date to program your fruitworm applications. Large, plastic Delta traps with interchangeable sticky inserts are recommended. Lures need to be attached with pins to the interior roof of the traps away from the sticky insert.

Upcoming meetings

The next Blueberry Pre-bloom Meeting is scheduled for May 11 from 5:30-7:30 p.m. in Ottawa County. For more information, see “Two blueberry management meetings scheduled before bloom.” More information on this May 11 meeting will follow soon, including the agenda and online registration instructions.

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