West central Michigan small fruit regional report – May 19, 2015

Blueberries are in full bloom and petal fall started in southern counties. Monitoring traps for fruitworms should be deployed. Delaying trap placement impairs proper timing of insecticide application against fruitworms.

Weather conditions have improved in west central Michigan and temperatures, although still colder than in May 2014, are moving steadily into the low 80s. With an increase in the maximum daily temperatures comes the need to prepare for managing fruitworms attacking blueberries at petal fall. Currently, early varieties like Duke and Bluecrop entered the petal fall stage at Allegan and Van Buren counties. Late-season blueberries like Elliott and Aurora are in full bloom stage at this time.

So far, no important blueberry disease problems have been observed despite the extent of the winter damage in most fields. Mummy berry, commonly present at this time, has not been observed in significant numbers.

Regarding fruitworm problems in blueberries, cherry fruitworms are emerging earlier than cranberry fruitworms. Below is a table with predicted degree days for the appearance of the first overwintering adults and the first eggs for both species in central and southwest Michigan.

Predicted degree days for appearance of overwintering fruitworm adults and first eggs.


First adults

First eggs

Current degree day accumulation (5/19/2015)

Grand Junction


West Olive

Cherry fruitworm

238 ± 30

432 ± 15




Cranberry fruitworm

375 ± 20

460 ± 20




As of May 19, 2015, our degree day models indicate that cherry fruitworm overwintering adults are already emerging in central and southwest Michigan. Based on the degree day accumulation for the next five days, eggs are still more than a week away. On the other hand, cranberry fruitworm overwintering adults are expected to emerge this week in Van Buren County around the Grand Junction, Michigan area and at other southern counties. Eggs are not expected yet.

Michigan State University Extension recommends growers visit the MSU Enviro-weather website and check the weather extended forecast and cranberry fruitworm degree day model for more up to date information on the progress of the fruitworm phenology in your area.

Bee-safe insecticides to be used at this time for cherry fruitworms and cranberry fruitworms include Grandevo (1-3 pounds per acre) and Venerate XC (1-2 quarts per acre). Reduced-risk insecticides like Confirm 2F (16 ounces per acre) are moderately toxic to bees and should be used with care and avoid applying them over bees in the field or hives. For more insecticide options and recommendations, please consult the “2015 Michigan Fruit Management Guide” (E-154).

Contact your local MSU Extension office or me at 616-260-0671 or garicias4@msu.edu for additional questions.

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