Module 2: Disease Management
Module 1: Biology, symptoms, and Diagnosis
Welcome Module 3: Phytophthora ramorum Conclusion Take the Exam Further Information

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The water mold Phytophthora ramorum is an invasive pathogen that recently became established in the United States. Phytophthora ramorum affects a wide range of woody, perennial plants including forest, landscape, and nursery plants. It is the cause of several plant diseases, including Ramorum leaf blight, Ramorum dieback, and—the most widely known—sudden oak death.

Phytophthora ramorum has already killed more than 1 million forest trees in California, and it has spread to one forest location in the southwest corner of Oregon. Phytophthora ramorum also has been found in some nurseries in Europe and British Columbia. To date, the disease has not become established in forests outside the West Coast

Infected coast live oaks in Marin County, CA. Infected coast live oaks in Marin County, CA.

Photo by Marin County Fire Department.
P. ramorum infected nursery plants being incinerated on-site.
Nursery plants infected with Phytophthora ramorum are being incinerated on site.

Photo by J. Hedberg

Forests and wooded landscapes are at greatest risk from Phytophthora ramorum. Because infected nursery plants could spread the disease to forests, it is very important to prevent Phytophthora ramorum from contaminating nurseries. Before the disease was identified and tracked, infected nursery plants from the West Coast were shipped to many other states. Now, plant movement from these areas is subject to regulation.

Phytophthora ramorum has impacted nurseries in several ways. West Coast nurseries shipping plants out of state must comply with federal regulations, which are covered in detail in following sections. The disease has also affected production practices and marketing. If a nursery is found to be infected with Phytophthora ramorum, infected plants must be destroyed, which can be very costly.

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