Phytophthora Root Rot of Juniper

Scientific name: Phytophthora austrocedri 

Phytophthora austrocedri causes root rot, crown rot, and death of plants in the cypress family. All species of juniper are believed to be susceptible to infection, along with Port Orford cedar (Chamaecyparis lawsoniana), Alaskan cedar (Xanthocyparis nootkatensis), and several cypress species.

Phytophthora root rot of juniper has been observed in natural forests and in nursery plants. 

Distribution

Phytophthora austrocedri was first identified in 2007 in Argentina where it was causing death of Chilean cedar trees. Shortly after, it was found killing juniper trees in northern Britain. Neither country is believed to be the origin of this plant pathogen.

Phytophthora austrocedri was first identified in the United States in 2024 in nursery grown junipers in Oregon, and in 2025 in a Wisconsin nursery. It is unknown how widespread P. austrocedri is in the United States. The origin of this invasive plant pathogen is unknown.

Biology

Phytophthora austrocedri is an oomycete, also known as a water mold. Oomycetes are fungus-like organisms that thrive in waterlogged and wet conditions. Little is known about the biology of P. austrocedri. However, most species of Phytophthora spread through water, contaminated soil, and infected plant materials. Phytophthora austrocedri has been isolated from soil around infected trees and from plants in nurseries. Long distance spread likely occurs through the movement of infected plants.

Phytophthora austrocedri attacks the roots and crowns of host trees and can move up into the lower trunk and branches. The pathogen infects and kills the vascular system of the plant, resulting in wilt and death of the canopy.

Identification

Infected junipers may show dieback and browning of scattered branches or the entire canopy. Remove the bark from the lower stem near the soil line. The sapwood may appear orange-brown and may contain pockets of sticky resin. Healthy sapwood is white. A laboratory test is required to confirm the presence of Phytophthora austrocedri.

Regulatory Status

Phytophthora austrocedri is no longer regulated at the federal level. If found in nursery plants in Minnesota, infected plants would be regulated under state nursery laws.

Reporting Phytophthora Root Rot of Juniper

If you suspect you have found Phytophthora root rot of juniper:

• Email pictures, your name, and the location to reportapest@state.mn.us
• Or report online at www.mda.state.mn.us/reportapest

The Minnesota Department of Agriculture (MDA) may contact you to request a sample for laboratory testing to confirm the diagnosis.