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Foreign phytophthora strain found at Wisconsin plant nursery

Wisconsin officials say a foreign plant disease has been found at a Washington County nursery.

The Department of Agriculture, Trade, and Consumer Protection says Cypress Mortality is a disease caused by the pathogen Phytophthora austrocedri, and affects common nursery plants like Juniper, Arborvitae, and False Cypress.  The Washington County infection caused severe damage to a field of Star Power Juniper plants.

This strain of Phytophthora was first found in the United States in 2024 in Oregon.  Before that, the disease had only been detected in Argentina in 2007 and in the U.K. in 2012.

DATCP officials say people who purchase or grow arborvitae, juniper, or false cypress should monitor plants for P. austrocedri symptoms, including:

• Stunting
• Dull green or yellowish foliage in early infections
• Branch flagging and reddish brown/bronze foliage in advanced infections
• Lesions or cankers at the base of the plant or branch
• Orange/brown discolored wood tissue under bark from lesions or cankers

This pathogen is spread through infected plants, soil, and water. Care should be taken when working with these hosts to prevent the accidental spread of this disease during routine activities, such as moving plants and pruning.