Thrips showing up in some blueberry fields

These small insects are rare but can injure flowers and fruit.

Flower thrips have been reported in a few isolated Southwest Michigan blueberry fields this past week. These tiny insects tend to be found on the flowers and also inside the flowers where their feeding can lead to flower abortion and scarring of the fruit that develop from these flowers. Learn more about flower thrips and their damage at MSU’s Michigan Blueberry Facts website.

To scout for thrips, look on the outside of flowers and break open flowers to look inside. These are small insects (1 to 2 mm) and you will require a hand lens to see them clearly. Shaking flowers over a white tray is an effective method for determining whether there are thrips inside the flowers. This will provide a presence or absence result, but there are no economic thresholds yet developed for this pest on blueberries.

We have relatively little experience with thrips control in Michigan because these insects tend to be a rare problem, with significant infestations once every 10 years or so. In previous trials at Michigan State University run by John Wise, SpinTor (spinosad) was a very effective insecticide. The more recently-registered insecticide Delegate, which is a similar type of insecticide, also lists thrips on the label. Spinosad products are generally considered as more effective against thrips, but Delegate is expected to have greater residual activity. Additionally, the organic insecticide Entrust (spinosad) is labeled for thrips control. With each of these products, it is advisable to use an adjuvant to help with spreading and to ensure good coverage.

Because thrips tend to be active during bloom when bees are in the fields, extreme caution should be used when attempting chemical control during this time of the season. Weigh up the level of damage being observed by the pest and consider the risk to pollinators. Application in the late evening after all the bee activity is finished for the day will allow the residues to dry before bee activity the next morning. For example, the Entrust label states that the product is toxic to bees for three hours following application.

Dr. Isaacs’s work is funded in part by MSU’s AgBioResearch.

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