Fruitworm flight activity started, egglaying predicted in earliest blueberry sites

Monitoring and degree-day models can inform spray timings.

As petal fall starts in blueberries and fruit starts sizing, the new berries can be infested by two fruitworm species—cherry and cranberry fruitworm. Within the past 10 days, sites in southwest Michigan have reported the biofix for cherry fruitworm moths, which is usually flying a week or more before cranberry fruitworm. Over the Memorial Day weekend, the first reports of cranberry fruitworm moth activity was reported from Grand Junction, Bloomingdale and from our monitoring traps at the Trevor Nichols Research Center in Fennville, Michigan. Grand Junction is usually much more advanced in development than sites closer to Lake Michigan or further north. With the current high temperatures and warm nights, we expect that fruitworm activity will progress rapidly.

There are two degree-day models for these pests online at Michigan State University Enviroweather. For Grand Junction, assuming the cranberry fruitworm moths were trapped on Friday evening, May 25, the model is predicting egglaying to start yesterday. With further good weather today and tonight, growers with a history of fruitworm challenges in their blueberry fields should protect their fruit using one of the options registered for use during bloom, as we described in “Fruitworm control in blueberries” from MSU Extension, published May 15, 2018.

One of the most effective options for this timing and these pests is Intrepid 2F, which can be applied at 12 ounces per acre with a spreader sticker to improve coverage and also reduce the loss during the upcoming rainfall. Intrepid is relatively rainfast, so we expect this application to retain activity unless there is very intense rain after the application. New fruit that develop in the coming weeks from current flowers will not be protected (this is not a systemic insecticide), so high pressure fruitworm sites may require additional treatment before full petal fall when there are more insecticide options for fruitworm control.

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