Using the plum curculio model to assist with management decisions in tart cherries

Plum curculio are active in northwest Michigan and we have observed oviposition in several tree fruits. Scouting is essential if using Enviro-weather’s plum curculio model.

MSU Enviro-weather’s plum curculio model can assist tree fruit growers in managing plum curculio.
MSU Enviro-weather’s plum curculio model can assist tree fruit growers in managing plum curculio.

Weather in northwest Michigan has been steadily warm with variable moisture, and these conditions have been conducive for insect development and movement into orchards. Daytime and evening temperatures above 60 degrees Fahrenheit and moisture increase plum curculio activity. We have observed plum curculio feeding damage and oviposition scars in apricots, sweet and tart cherries and apples, and many growers are applying an insecticide to manage this pest.

Some growers and consultants use the plum curculio model on Michigan State University’s Enviro-weather to assist with timing plum curculio sprays. This model was developed as a postponed insecticide treatment strategy for plum curculio, and scouting is critical for using this model effectively. Because conditions have been ideal for plum curculio activity, and most tree fruits are at a susceptible stage for plum curculio egglaying, growers and consultants should be actively scouting for plum curculio. MSU Extension recommends scouting be used in conjunction with the model rather than solely relying on the model to make management decisions. This model assumes that an intensive scouting program be used along with growing degree-day (GDD) accumulations, and orchards with a relatively higher plum curculio population or hot spot blocks adjacent to woodlots may need management sooner than the model suggests.

The plum curculio model is specifically for use in tart cherries as it is based on tart cherry development and predicted emergence of plum curculio. At late bloom/petal fall timing, growers and consultants should begin scouting for plum curculio, particularly with temperatures above 60 F with rain or high humidity. Scouting should continue to determine actual plum curculio presence and density, and the model can be used as a reference for management.

To use the plum curculio model, locate the date of full bloom to establish a biofix. This season, the Northwest Michigan Horticulture Research Center biofix was May 17. Follow the corresponding column downward to determine the growing degree-day accumulations as well as the predicted accumulations according to the forecasted temperatures. Currently, the model shows that the Northwest Michigan Horticulture Research Center has accumulated 221 GDD base 50 F. According to the model, management is recommended at 375 GDD base 50. All plum curculio eggs laid prior to 350 GDD will hatch into larvae, and the infested fruits will drop from the tree and will not be present at harvest time.

If we were to rely solely on the model, plum curculio management at the Northwest Michigan Horticulture Research Center would not occur until sometime after June 6. However, we actively scout for plum curculio, and we have already observed plum curculio oviposition in tart cherries. As a result, we are applying insecticides for plum curculio management at this time.

Knowing the history of an orchard’s plum curculio pressure, monitoring weather conditions and conducting an intensive scouting program are all key factors that influence management decisions. By monitoring these factors, growers and consultants can use the Enviro-weather model to delay or postpone plum curculio management until 375 GDD base 50 after biofix.

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