West central Michigan small fruit update – May 21, 2019

Pollination, stem gall wasp, fruitworm and disease management are main priorities for blueberry growers that require time and resources this time of year.

Weather conditions in west central Michigan remain cold and breezy with some patchy frosts in low areas that have not affected blueberries, strawberries and raspberries. For the past seven days, average daily minimum temperatures were around 44 degrees Fahrenheit and the daily maximum averaged 68 F. Climatic conditions during the same period also included some rains that left an accumulation of 0.5 to 0.9 inch of rain. Most of this was in the form of drizzle, except for May 18 when a moderated rain left behind an accumulation of 0.5 to 0.6 inch in some areas.

Due to the prevailing daily temperatures, growing degree day (GDD) accumulation base 50 remained at a minimum. So far, GDD accumulations in west central Michigan are 184-186 GDD. However, around Grand Junction, Michigan, the accumulation is 270 GDD. There is almost a 100 GDD difference between the Holland-Fennville area and Grand Junction. Growers need to take into consideration this difference when planning their integrated pest management (IPM) and crop management activities.

Strawberries around west central Michigan started blooming. Flower buds have emerged and some flowers are already visible. Although low temperatures in the region have delayed the bloom period, so far no frost damage has been reported or observed in most fields. Temperatures in the region have remained well above freezing and growers do not anticipate any damage to their fields due to weather conditions.

Raspberries continue developing. Shoot growth remains active and without major problems.

Blueberries, on the other hand, are at different bloom stages depending on the variety and location. North of Allegan County, early varieties started blooming, and Elliott, Liberty, Aurora and Bluecrop are at the late pink stage. However, for most varieties, full bloom is expected by the end of this week.

For blueberry growers, one of the main priority at this time of year is fruitworm management. Cherry and cranberry fruitworm started emerging from their overwintering sites. Pheromone trap inspection should be twice a week instead of once a week until the first moths are caught in the traps. The day when the first moths are trapped is the day to begin the GDD accumulation to predict the beginning of fruitworm oviposition period. The day of the first catch is what we call the “biofix.”

Below are the current forecasted events on the life cycle of both cherry fruitworm and cranberry fruitworm. Use this information as a guide to program your fruitworm control program.

Current GDD accumulation (base 50) since March 1 in west central Michigan is 184-86 GDD around the West Olive-Fennville area. Around the Grand Junction area, it is already 270 GDD.

Visit Michigan State University Enviroweather to get updated information on current and forecasted GDD accumulations. Also, check the cherry fruitworm and cranberry fruitworm models for oviposition starting period predictions.


First adults

First eggs

Current GDD accumulations as of May 14, 2019

Grand Junction


West Olive

Cherry fruitworm

238 ± 30

432 ± 15




Cranberry fruitworm

375 ± 20

460 ± 20




2019 Blueberry Bloom Meeting: Pollination and other early season issues

MSU Extension will hold a field workshop on blueberry pollination and other spring issues at the Trevor Nichols Research Center on Tuesday, May 23, from 12 to 4 p.m. This will include presentations by MSU research and Extension staff on weather, nematode pests and sampling methods, honey bee colonies and management, wild bees and sampling for pollination and fruit rots management. The meeting will start indoors at the main education building at noon, include a light lunch and then we will move outside for field presentations at the research center’s blueberry planting. Be prepared for standing outdoors for some time and moving between stations. We will have a setup for shade and seating available.

There will be two RUP recertification credits for attending this training. 

There is no cost for this meeting, which is free and open to all. To ensure an accurate lunch count, please pre-register online.

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