Phytophthora ramorum FAQ's

What is Phytophthora ramorum? P. ramorum, or Sudden Oak Death, is a forest disease caused by a fungus-like pathogen. This pathogen has caused widespread dieback of tanoak and several oak species in the central and northern coastal counties of California. It has also been found on other species. While some of these species - coast live oak, black oak, Shreve oak and tanoak - sustain lethal trunk infections, other plants get more benign foliar and twig infections.

What does Phytophthora ramorum look like? Depending on the plant species, infection may occur on the trunk, branches, and/or leaves. Infections on woody portions of the tree are referred to as cankers. Cankers on the trunk of oak trees are the most damaging. Tree death appears to occur when cankers expand in the trunk (girdling) and disrupt physiological function. Diseased oaks are often attacked by other pest organisms -- fungi that decay sapwood (Hypoxylon thourasianum) and bark beetles. In the shrub species the symptoms can range from leaf spot to twig girdling, and do not necessarily result in death of the plant. Phytophthora ramorum appears to thrive in cooler, wetter climates.

Does P. ramorum kill all of the species it infects? Symptoms caused by P. ramorum are of two types. It causes cankers mainly on the trunk on true oaks and tanoaks which may expand and eventually girdle the trees and kills them. On most of the other hosts, however, it is a foliar disease that causes leaf blight, but does not kill the plant. These foliar hosts are very important in disease spread. Under moist conditions, the pathogen sporulates prolifically on the leaves and the plants serve as reservoirs of inoculum. Since the host is not killed, these plants may serve as source of inoculum for a long time. Tan oak experiences both the foliar blight and bole cankers which may explain why tan oak, are particularly susceptible. Also when rhododendron and other plants are small, and tissues tender such as seedlings and bedding plants they may be killed by P. ramorum.

Is P. ramorum toxic to humans or other animals? No

What other conditions might be confused with Phytophthora ramorum? Not all sick or dead oak trees have P. ramorum. A bacterial infection known as wetwood causes bleeding in the trunks and large branches of oak trees, and can resemble the bleeding associated with P. ramorum. Hypoxylon is a fungus that grows on dead wood. It is often associated with the later stages of P. ramorum, but can appear on the trunks of trees or logs that are dead or dying from any number of causes. It is characterized by dark brown to black globules, up to the size of a quarter. Other oak diseases exist in parts of the U.S., and oaks commonly may be seen dying from other causes, such as root damage resulting from construction activity or other disturbance.

The foliar hosts (such as rhododendron) can also be damaged by the sun or other fungi that cause similar symptoms on leaves, making P. ramorum very difficult to diagnose on these species. Bigleaf maple, buckeye and redwood all naturally shed foliage. Buckeye are summer deciduous, they loose their leaves in the summer. Maples and redwood may turn brown in the summer or early fall in response to drought conditions. This will make them look sick, but this is normal for these species.

Information provided by: http://www.aphis.usda.gov/ppq/ispm/pramorum/

http://www.suddenoakdeath.org/

- compiled by the American Nursery  & Landscape Association (ANLA)  www.anla.org   4/5/04

Diagnostic guide on identifying SOD infected plants:phytophthora_ramorum_faq.htm

Sudden Oak Death links list, press releases, etc.: http://www.invasive.org/sod.cfm

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Last modified: 10/26/03