NC STATE UNIVERSITY
College of Agriculture and Life Sciences
Department of Plant Pathology
Extension

Sudden Oak Death in the Landscape

Dead coast live oak and tanoaks due to Sudden Oak Death in Big Sur, California Close up of bleeding canker on oak tree
Dead coast live oak and tanoaks due to Sudden Oak Death in Big Sur, California (left) and close up of bleeding canker (right) on oak tree. (Photo credits to Joseph O'Brien, US Forest Service)

Where picturesque oaks once stood, tens of thousands of ashen gray trees dot the hillsides along the northern California coast, victims of a disease called Sudden Oak Death. An unsettling reminder of what could happen in the southern Appalachian forests if the organism that causes Sudden Oak Death is introduced into North Carolina's native and urban forests.

Although Sudden Oak Death (SOD) is a forest disease, the organism that causes this disease is capable of infecting a large number of woody ornamental plants that are commonly sold by nurseries and planted into urban landscapes.

In the past, the NC Department of Agriculture & Consumer Services has confirmed that the fungus-like organism causing Sudden Oak Death, Phytophthora ramorum (pronounced Fi-TOFF-thor-ra ra-MOR-um), was introduced into the state in shipments of infested nursery stock from southern California.

Because the potential exists for inadvertent introduction of P. ramoum to the landscape, consumers should be aware of the threat. But to date, however, Sudden Oak Death disease has not been detected in any landscapes in North Carolina.

Homeowners and landscape professionals can submit leaf samples for SOD diagnosis thorough their local North Carolina Cooperative Extension office. The North Carolina Department of Agriculture and Consumer Services will process suspect plant material for diagnosis.

  • Collect no more than 20 leaves per plant. Do not collect healthy appearing leaves as these cannot be tested. Likewise avoid collecting completely dead leaves.
  • Collect leaves with suspect leaf spots and place them in a plastic "ziplock" bag and
  • Take them to your local Extension Center along with a submission form.
  • Do not return any plants or leaf samples to the nursery or garden center where they were originally purchased.
  • Do not move, dig, or destroy any plant that has already been planted in the landscape. Moving a plant could result in spreading the disease organism to other locations.
  • Do not compost the plant or put it with yard clippings for curbside pickup as those materials may be mulched and spread back into the landscape. Fallen leaves should be collected, sealed in a plastic bag, and discarded with your household trash.

Background:

Despite the name, Sudden Oak Death disease is not just restricted to oaks.

Camellias, rhododendrons, Pieris, mountain laurel, viburnum, and lilacs are among 60 different plant hosts or potential carriers of the disease.

Only above ground plant parts are affected. The roots of infected plants remain healthy.

On oaks, the organism causes bleeding cankers on the trunk that can eventually girdle and kill the tree. On the majority of host plants, however, the disease causes leaf spots and twig dieback, but very rarely results in plant death.

Infected oak and tan oak trees in California forests are typically found in close proximity to other host plants such as bay laurel that have infected leaves. As such, it would be unusual to have an infected oak tree with a bleeding canker without the presence of other nearby foliar plant hosts such as mountain laurel or camellias. The disease is not known to spread from oak to oak.

Symptoms:

Camellia

The appearance of the leaf spots can be quite variable on Camellia. Generally the leaf spots are light to dark brown in color, may appear to be greasy, and often start at the tip of leaf and progress down the middle of the leaf toward the point of attachment. As the disease progresses, concentric rings of dead tissue may be observed on the infected leaves. Infected camellias may also drop their leaves, leaving sparse or barren stems.

Camellia

Viburnum

The disease on Viburnum is somewhat variable, but the leaf tips are often affected first, and the brown discoloration spreads toward the base of the leaf in a V-shaped pattern. Tissue may initially appear soft and wet, but will become dry with age. Small branch tips may also be killed, causing the foliage to wilt. (Note: hole punches in leaves were made to remove leaf disks for analysis for Phytophthora ramorum the cause of Sudden Oak Death.)

Viburnum

Rhododendron

On rhododendron, brown leaf spots with diffuse margins often start at the tip of the leaf and move toward the petiole along the midrib. The tips of the branches may also become infected and spread from the petioles to the leaves resulting in v-shaped lesions starting at the base of the leaf. Affected branch tips may turn brown and wilt. (Note: hole punches in leaves were made to remove leaf disks for analysis for Phytophthora ramorum the cause of Sudden Oak Death.)

Rhododendron

Additional Information