USA NPN National Phenology Network

Taking the Pulse of Our Planet

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Hemlock Woolly Adelgid Forecast

Hemlock woolly adelgid can be deadly to hemlock trees and, in the eastern United States, lacks enemies that keep their populations in check. Researchers wish to identify the optimal window to release insect predators; you can support this effort by observing hemlock woolly adelgid life cycle stages using Nature’s Notebook

Hemlock Wooly Adelgid Current Day Forecast.

Hemlock Wooly Adelgid 6-Day Forecast.

Pheno Forecast maps show when management actions should be taken for key pest species. These maps are updated daily and are available 6 days in the future.

Pheno Forecasts are based on published growing degree day (GDD) thresholds for points in pest life cycles when management actions are most effective. Forecasts are currently available for five insect pest species.

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

Hemlock woolly adelgid (Adelges tsugae) damages hemlock trees by piercing the twig at the base of the needles and sucking sap from the trees. It occurs in forests in the eastern US as well as in the Pacific Northwest. In the Northwest, it is kept in check by natural predators; in the east, where predators are few, this pest is causing major damage to hemlock forests. Researchers are working to identify the best time of year to release predator insects or biocontrols, that would limit the rapid spread and damage of the hemlock woolly adelgid.

Treatment Summary

The Pheno Forecast map indicates when you will be most likely to see hemlock woolly adelgid eggs and active nymphs. GDDs are accumulated from a base temperature of 32oF.

More information on map development and re-use policy. 

Explore HWA Forecast