West central Michigan small fruit regional report – May 3, 2016

Current weather conditions in west central Michigan remain around the upper 50s with some days in the low 60s with periods of rain, slowing down insect pest development and plant growth.

As of May 3, 2016, small fruit crops are at early stages of growth. Blueberries have continued developing but at a slow rate due to cool temperatures that have prevailed for the most part of April and the first days of May. During the past five days, the average minimum temperature has been around 40 degrees Fahrenheit and the maximum around 58 F. So far, based on the prevailing weather conditions, growing degree-day (GDD) accumulation as of May 3 are 159 GDD base 50 F.

Regarding precipitation, there have been some small rains and drizzle conditions, allowing an accumulation of around 1 inch of precipitation during the past week, which brings the total accumulation to 10 inches since Jan. 1. Last week there was a patchy hailstorm that affected several farms in the Grand Haven-Holland area, causing considerable damage in some fields. However, the extent of the damage will be unknown until weather conditions warm up and the effects on the plant structure and flower buds becomes evident.

Currently, blueberries in west central Michigan are in the early bloom stages. For example, Bluecrop is at 5-10 percent bloom and Jersey and Elliott are in the late pink bud stage. Because of the observed prolonged periods of cool and wet weather, the risk of fungal infections, especially mummy berry shoot strike, remain high. Growers that have not completed the fungicide treatment for mummy berry shoot strike and Phomopsis twig blight need to do it as soon as weather and soil conditions allow it.

At this time, the recommended fungicides against mummy berry shoot strike and Phomopsis twig blight are Indar, Quash, Proline and Tilt. Special attention should be placed on blueberry fields that were damaged by last week’s hailstorm. Hail-damaged canes can be easily infected by mummy berry and Phomopsis twig blight or other fungal or bacterial infections. For product recommendations including doses and special handling recommendation, please check the 2016 Michigan Fruit Management Guide (E0154) by Michigan State University Extension.

For insect pests in blueberries, the emergence of cherry fruitworm and cranberry fruitworm has been delayed due to prevailing cool weather conditions that have allowed a daily GDD accumulation of no more than three to five GDDs per day. As soon as the weather warms up, cherry fruitworm and cranberry fruitworm will start emerging from diapause. Thus, according to our phenology models (see table), we expect the first cherry fruitworm adult emergence in the Grand Junction, Michigan, area by the end of this week or earlier if the weather allows.

Fruitworm development in Michigan according to phenology models


First adults

Second eggs

Current GDD accumulation (5/03/2016)

Grand Junction


West Olive

Cherry fruitworm

238 ± 30

432 ± 15




Cranberry fruitworm

375 ± 20

460 ± 20




For fruitworm management, follow the MSU Extension recommendations:

  • Use a monitoring program for pest distribution and biofix.
  • Use the GDD model for improved spray timings.
  • Use insect growth regulators insecticides for selectivity for use during bloom.
  • Use reduced-risk insecticides for control of fruitworms and other overlapping pests.

For Ottawa, Muskegon and Oceana counties where the stem gall wasp is a serious problem in Jersey fields and other susceptible varieties, consider integrating this insect pest into your early fruitworm integrated pest management program. That may include using insecticides such Intrepid or Confirm for the first application against fruitworms at 50 percent petal fall, and Lannate, Assana XL or Danitol for the second application right after the removal of the bees from the field. For doses and recommendations for protecting bees and natural enemies from non-target impact of insecticides, consult the 2016 Michigan Fruit Management Guide (E0154). You may also get assistance from your local MSU Extension office, or you may contact me at 616-260-0671 or .(JavaScript must be enabled to view this email address).

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