Scientific name: Phytophthora ramorum

Native range: unknown

At Risk

Oak trees have been the most susceptible hosts for sudden oak death in the U.S. but many other plants can also be infected and carry the pathogen.


Sudden oak death was first officially reported in California in 2000 and was found in Europe around the same time. However, it is not clear that it originated in North America or Europe. In the U.S., sudden oak death is now known to occur in California, Oregon and Washington. Although the primary impact has been on oak, many other plants can carry sudden oak death and the importation of infected plants could introduce the pathogen to new areas.


Sudden oak death does well in cool, wet climates like can be found in coastal northern California. Nurseries appear to also provide suitable habitat. In Minnesota, greenhouses and nurseries are likely at greatest risk for problems with sudden oak death. Once a nursery is infected with sudden oak death it has proven difficult to eradicate and can affect a nurseries ability to export and sell plants.

The sudden oak death pathogen likely spreads between plants during rainfalls or watering, when spores are splashed by water drops. After entering a tree through its leaves, the pathogen moves through the bark, killing phloem and cambium tissue that transports food throughout the plant. Eventually the infection makes its way around the entire trunk, girdling and killing the tree. Secondary pests (insects) can also attack the stressed plant, causing further damage by reducing the flow of water at the surface. 


Sudden oak death was first named after the short period (six to eight weeks) it takes for infected oaks leaves to turn from green to brown. The most likely way that sudden oak death would occur in Minnesota is after importation of infected plants. Identifying sudden oak death is not easy and will require expert laboratory analysis.

A number of other more likely problems affect oak trees in Minnesota and should be considered when diagnosing potential problems:

  • Oak Wilt is a common problem for oak trees in southeastern Minnesota and the Twin Cities Region.
  • Bur oak blight is a recently discovered problem and has been confirmed to occur throughout Minnesota.
  • Other Phytophthora species besides sudden oak death can also impact oaks and other trees in Minnesota.

For help diagnosing problems on oak trees, consult the University of Minnesota “What’s Wrong With my Plant?” for oaks.

Regulatory Status: Regulated

Sudden oak death is regulated at the state and federal level. States with known infections and USDA APHIS regulate the movement of host nursery stock from infected nurseries to prevent the movement of sudden oak death to other areas.

What Can I Do? 

Contact the Minnesota Department of Agriculture via Arrest the Pest if you suspect you have found Sudden Oak Death.