West central Michigan small fruit update – May 30, 2017

Blueberry bloom period is coming to an end. Removing pollinators before starting your insect pest control is critical to protect bees and other pollinators from pesticide exposure.

Weather conditions in west central Michigan have remained relatively stable, with daily average temperatures in the low 60s and a few showers with no significant rain accumulation. For the past seven days the average minimum temperatures have been 52 degrees Fahrenheit and the average maximum temperatures around 72 F. Cumulated precipitation during the same period was 0.24 inch for a total accumulation of 12.8 to 15.7 inches since Jan. 1, 2017.

Most blueberry fields are at the green fruit stage with late-season varieties still in the petal fall stage. In other words, the bloom period is over. Thus, honey bees and bumble bees need to be removed from fields in preparation for managing the cherry fruitworm and cranberry fruitworm.

Wisely use your insecticides; we need to place special attention to the chemical characteristics of insecticides we are using at this time. Before determining which insecticide to use for cherry fruitworm and cranberry fruitworm control, check the weather conditions, the stage of the fruit and other insect pests already present in your blueberry fields.

This season, fruitworms are showing up almost at the same time that facilitate their control. One single application of insecticide will be enough to control this problem right after petal fall. A second application after honey bees have been removed from the field can be made with a broad spectrum insecticide.

Current weather conditions as those previously described (daily average below 70s) will not be conducive for an optimum control of fruitworms using B.t. (Bacillus thuringiensis). In order to be effective, larvae need to ingest the product in quantities enough to stop the feeding and, later on, cause insect death.

Low temperatures like the ones we are experiencing now cause arrestment in the insect and feeding is slowed down or stopped. Thus, not enough B.t. is ingested to cause a rapid paralysis of the insect feeding. B.t. will be most effective for the second application when daily temperatures are already in the upper 70s or low 80s.

If there is a concern for the presence of honey bees in the field, try using other insecticides like Sivanto 200SL (7 – 10.5 fluid ounces) or Assail 30 SG (4.5 - 5.3 ounces). Assail needs to be sprayed during the evening when bees are not foraging. Also, if your fields have extensive presence of shoestring virus transmitted by aphids, Assail will also care of this pest. For a complete list of recommended insecticides, please consult Michigan State University Extension bulletin E0154, “2017 Michigan Fruit Management Guide.”

Below is a table with the predicted degree-days when we are expecting the emergence of cherry fruitworm and cranberry fruitworm adults, as well as their egglaying period. It also includes 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 (5/30/2017)

Grand Junction


West Olive

Cherry fruitworm

238 ± 30

432 ± 15




Cranberry fruitworm

375 ± 20

460 ± 20




* Adults are already emerging in Ottawa, Allegan, Van Buren and other southern counties. Cherry fruitworm egglaying already started at all sites. Cranberry egglaying is predicted to start this week in Allegan and Van Buren counties.

2017 systems approach to manage spotted wing Drosophila (SWD): IPM training for berry growers

We would like to remind our growers about attending the 2017 Spotted Wing Drosophila Workshop on Monday, June 5, 2017, from 9 a.m. to 4 p.m., in the training room at MSU Trevor Nichols Research Center, 6237 124th Avenue Fennville, MI. Because of the mild winter conditions we had in 2016-2017, we expect an early arrival of spotted wing Drosophila in our berry crops. That could translate into a longer protecting period against this pest.

We recommend growers participate in this training since controlling SWD remains a major issue for most of the industry. Learning to adjust their pest control program according to changing conditions of weather, plant and insect phenology is critical to save money, resources and obtain a successful SWD control.

For the full agenda and to register online, go to 2017 Spotted Wing Drosophila Workshop.

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