Don’t delay blueberry fruitworm management decisions

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Checking monitoring traps for cherry fruitworm and cranberry fruitworm at three farms in Van Buren county yesterday (June 4) has revealed the expected increase in moth catches over the past week. Eggs of both species were also found during detailed scouting of the bushes, indicating that fruitworm pest development is progressing and blueberries are at risk from larvae penetrating the fruit. While many growers are already acting to protect the crop from fruitworms, those that have waited until bees are removed should consider some action in the light of our recent findings from monitoring and scouting for these pests.

For cherry fruitworm, which is the earlier developing species, traps have caught moths for the fourth week in a row with some sites having a significant increase in catches (15 moths) from the past week. Egg laying has been very high, with fourteen eggs detected at one farm during scouting for one minute on 30 bushes. This is the highest level of cherry fruitworm egg laying experienced in recent years in Michigan, making the early ripening varieties at particular risk from having larvae infesting fruit during harvest.

Cranberry fruitworm moths in traps have increased this week, with the maximum catch over the past week at sixty-six. This is also a high level of moth activity, and is coupled with the second week of finding cranberry fruitworm eggs during the bush sampling. This also provides some strong evidence that blueberry fields are at risk from fruitworm larvae infesting the fruit.

The levels of moths and eggs detected indicate that fields with infestation from either cherry fruitworm or cranberry fruitworm in the past should be considered for an application of B.t. or Confirm if bees are still present, or an application of a broad-spectrum insecticide if bees have been removed already. Our research sites in Ottawa Co. have not been scouted yet this week, but cherry fruitworm egg laying was detected there last week and cranberry fruitworm egg laying is expected to be underway.

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

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