How to Identify and Treat Sudden Oak Death

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While people on the West Coast probably hear a lot about sudden oak death, this is an important plant disease that everyone should have on their radar. Sudden oak death (SOD) is caused by an oomycete pathogen. Phytophthora ramorum. As the name implies, oak species (Quercus spp and The Natholitho Corpus spp.) are the most commonly affected plants in the United States, although more than 100 woody plant species can also host the disease, including Rhododendron species. It is a disease of particular concern because of its wide host range, high lethality rate, and complex management requirements. Once plants are infected, they do not recover. In California, entire mountains of oak forests have been killed by SOD, leaving behind dead, dry, fire-prone trunks.

Map of SOD areas
With about 90 species In the United States, oaks make up an important part of our landscape. According to a report shared by the U.S. Department of Agriculture’s Forest Service, there are large areas of threatened forests in the East that are susceptible to sudden oak death, in addition to areas on the West Coast where it is established. . Example: Christos Georgiou/shutterstock.com.

Where has sudden oak death become a problem?

The pathogen causing SOD has been documented in North America and Europe. According to SOD website developed by the Animal and Plant Health Inspection Service of the US Department of Agriculture. (USDA-APHIS), this pathogen has been reported in 16 counties in California (Alameda, Contra Costa, Del Norte, Humboldt, Lake, Marin, Mendocino, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano, ) is considered established in Sonoma, and Trinity) and in Curry County, Oregon. In 2005, shortly after the disease was first described, it was detected on nursery stock shipped from California to various other states. Nursery stock was destroyed, and quarantine protocols were established for all detected counties to prevent movement and spread of SOD.

Bleeding sap from tree bark
Symptoms Associated with Sudden Oak Death Symptoms are easy to spot and include reddish-brown sap on the stem and shooting or leaf wilting or death (below) at the plant tips. Photo: Joseph O’Brien, USDA Forest Service, bugwood.org

In Europe, SOD has been detected in Belgium, the Czech Republic, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Norway, Poland, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. Most of the discoveries have been made on imported or cultivated plants from other countries. It remains unclear how or where the pathogen was initially introduced.

Sod is wilting on the tips of the leaves.
Photo: Joseph O’Brien, USDA Forest Service, bugwood.org

What are the symptoms?

SOD may initially appear as root rot or crown rot diseases with wilting leaves. Symptoms associated with a P. ramorum Infection varies by host plant but usually involves vascular damage, disruption of normal water transport, wilting of leaves, and eventual death. Secondary pests and pathogens (insects such as boring beetles and opportunistic fungi, in particular) often colonize a diseased plant after it has already been infected. P. ramorummaking identification of the actual causal agent more difficult.

With oak, symptoms associated with SOD include pill wilting as well as the appearance of cankers along the trunk that “bleed” reddish-brown sap. Leaves that are often attached to branches and do not fall to the ground. The sap from the canker often stains the lower bark of the tree and can attract insects. The canker “bleeding” is more noticeable in the dry season, as it is washed away by the rain. Any of these symptoms can be caused by other pathogens, so it’s best to have your plant tested by a plant diagnostic laboratory in your state to confirm its presence. P. ramorum. A positive result may mean that surrounding vegetation will need to be destroyed to prevent the spread of SOD.

What should I do if I suspect sudden oak death?

First, remind yourself and those around you not to move wood to new locations, especially outside of counties previously listed as quarantine zones. Buy local, burn local. In addition to traveling on wood, the bacterium can fly on boots, motorcycle tires and muddy paws in infected soil. If you have been in a forest or natural area where P. ramorum If established, clean shoes, pets and belongings before leaving the area. Rinse thoroughly with water, and disinfect with soap or rubbing alcohol if available. Many parks in positive counties have signs, educational materials, and disinfection stations available at park entrances.

If you see signs of canker bleeding on an oak in a positive county, the tree should be removed and destroyed. If you see these symptoms on an oak in an area outside of one of these quarantine areas, please photograph the plant, document its location, and submit a sample to your nearest plant diagnostic laboratory. It’s part of it. National Plant Protection Laboratory Accreditation Program (NPPLAP). Call the lab first to confirm that it can accept regulated pathogens such as P. ramorum or direct you to the appropriate contact.


Nicholas Goltz, DPM, is a plant pathologist and Extension educator based in the northeastern United States, where he helps growers and homeowners find holistic and holistic solutions to plant problems.

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