West central Michigan small fruit update – May 28, 2019

Blueberries are in full bloom, but persistent low temperatures and damp conditions are challenging pollination activities. Supplemental bumble bee pollination is the best response to these conditions.

Strawberries in bloom with some berries in the green fruit stage
Strawberries in bloom with some berries in the green fruit stage. Photo by Carlos Garcia-Salazar, MSU Extension.

Current weather conditions in west central Michigan remain cold and damp. For the past seven days there has been little change in the prevailing weather conditions. Daily minimum temperatures fluctuated between 48 and 50 degrees Fahrenheit, and daily maximum temperatures fluctuated between 69 and 70 Fahrenheit. The warmest temperatures occurred around the southern part Allegan County.

The past seven days also presented light rains and drizzle. These conditions left a precipitation accumulation of 0.7 to 1.6 inches of rain. The highest accumulation occurred around the Fennville-Holland, Michigan, area. As a result of these climatic conditions, daily growing degree day (GDD) accumulation remained at a minimum, except for the area around Grand Junction, Michigan. Growing degree day accumulation since March 1 around the Fennville-Holland blueberry growing area was between 262-263 GDD. At the Grand Junction area, accumulation reached 367 GDD base 50. Because of the weather conditions, the progress of the bloom period in all small fruit crops has been slow.

Strawberries are still blooming but we are already seeing small green fruit, some are thimble sized (see picture). So far, no problems other than black root rot are seen or reported by growers. The black root rot damage is exacerbated by the presence of root feeding nematodes. Nematodes cause root lesions that become a port of entry for the black root rot fungus.

Bramble, on the other hand, are progressing despite low temperatures. Summer raspberries have flower clusters that are blooming and some green fruits can be seen.

Blueberries are in full bloom and pollination is important at this time. Cold and damp conditions could become an issue for honey bee pollination. Honey bees prefer warm and sunny conditions to effectively forage and help pollinate blueberries. This is the time when bumble bees are very effective for pollination in blueberries. Bumble bees, especially native species, do not mind working under cloudy and cold or windy conditions. Place some bumble bees in your field to support honey bee pollination during days when honey bees remain inactive due to adverse weather conditions.

Regarding insect pests, stem gall wasps just start emerging. MSU Extension entomologist Rufus Isaacs’ scouting team has reported the beginning of the stem gall wasp population dynamics. Keep in mind that stem gall wasp management needs to start as soon as pollinator bees are removed from the field. For recommendations and control options, visit Isaacs’ publication, “Blueberry gall wasp management guidelines for 2018.”

Other important pests are the cherry fruitworm and cranberry fruitworm. Currently, prevailing low temperatures are preventing the emergence of both insect pests. Although two weeks ago the emergence of a “suicidal” population of cranberry fruitworm was reported, no substantial captures have been reported in pheromone traps around the Fennville-Grand Junction area. Therefore, early catches of moths should be discarded, and the biofix for the start of GDD accumulation should be restarted after sustained captures of moths occur.

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 262-263 GDD around the West Olive-Fennville area. Around the Grand Junction area, it is already 367 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 28, 2019

Grand Junction


West Olive

Cherry fruitworm

238 ± 30

432 ± 15




Cranberry fruitworm

375 ± 20

460 ± 20




2019 Systems Approach to Managing Spotted Wing Drosophila in Berries

MSU Extension and Michigan Food and Farming Systems invite growers, field managers, pest consultants and everyone involved in insect pest management in blueberries, raspberries and strawberries to attend our first 2019 SWD IPM Workshop. The workshop will be offered on Wednesday, June 5, 2019 from 9 a.m. to 4 p.m. at the Southwest Michigan Research and Extension Center, 1791 Hillandale Rd., Benton Harbor, MI 49022.

The workshop is based on using advanced IPM tools to manage the SWD. These IPM tools translate directly to the bottom line; savings in pest control, fewer insecticide applications, and minimum crops losses due to SWD

The program will include a hands-on session dedicated to discussing a successful IPM program for SWD control using Enviroweather and MSU Extension resources provided during the classroom sessions. If you have a lap top computer or smart phone, please bring it with you for the hands-on session. At least one lap top will be available for those that may need one for the hands-on practice.

There is a $25 fee for this workshop that includes materials, lunch and refreshments. A registration link with workshop agenda will be provided soon. There will be four RUP recertification credits for attending this training

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