USA NPN National Phenology Network

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Apple damaged by an apple maggot

Apple maggot larvae cause damage to fruit and if left untreated, can affect the entire tree.

Image credit:
H.J. Larsen,

Apple Maggot Forecast

Apple maggot larvae cause damage to ripening fruit. If left untreated, these pest insects can spread across the entire tree. These insects primarily affect apple trees, but can also impact plum, apricot, pear, cherry and hawthorn trees. 

Apple maggot current day forecast

Apple Maggot Current Day Forecast.

Apple maggot six day forecast

Apple Maggot 6-Day Forecast.

Pheno Forecast maps predict key life cycle stages in invasive and pest species, to improve management efficacy.  For insect pest species, Pheno Forecasts are based on published growing degree day (GDD) thresholds for key points in species life cycles. These key points typically represent life cycle stages when management actions are most effective. These maps are updated daily and available 6 days in the future.

Help us improve these maps! Our Pheno Forecast map products are still in development, and we seek input on their performance in your area. Give your feedback on the sidebar on the right side of this page.

Species Background

Native to the eastern states, apple maggot (Rhagoletis pomonella) is widespread throughout the U.S. In late spring and summer, adults emerge from the soil and lay eggs in apples. The larvae tunnel into the fruit, causing decay and rot.

Female apple maggot, Photo: Joseph Berger,

Adult Forecast

We forecast adult emergence based on growing degree days. Apple maggot can be controlled by bagging the fruit, trapping, and spraying with pesticide. In all cases, treatments are most effective if initiated as adults are starting to emerge from the soil. Ideally, treatments are undertaken prior to egg-laying, which occurs ~8-10 days after emergence. The Pheno Forecast map indicates when apples should be protected from maggots using mechanical or chemical methods. 

For specific information on preferred treatment options in your region, we recommend contacting your local extension agent. For more information, visit University of Minnesota ExtensionMichigan State University Extension, or Washington State University Tree Fruit Research & Extension Center 


GDD threshold

Base temp

Start date

GDD method

Model origin


Adult emergence



March 1

Simple average


Wise et al. (2010)

More information on map development and re-use policy.

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