Sudden Oak Death (SOD): Key Points

Oak tree in forest suffering from sudden oak death.
Sudden oak death (SOD) has killed millions of trees (mostly oak and tanoak) in California and Oregon since its discovery in the mid-1990s. (Photo courtesy of Joseph O'Brien, USDA forest service, Bugwood.org)
  • Symptoms and Causes

    Sudden oak death is caused by an invasive fungal pathogen:  Phytophthora ramorum. Symptoms include bleeding cankers on tree trunks, browning leaves and trees appearing to die quickly.

    The same pathogen also causes Ramorum blight on wide variety of other plants.  Symptoms vary depending on the host plant and include leaf spots, leaf blights and twig dieback.

  • Problem Areas

    The fungus was recently detected on rhododendron nursery plants that had been shipped into Nebraska.  It has NOT been found on established plants in any natural or landscaped area in the state.

    Risk of SOD to Nebraska trees is low due to our relatively dry climate. However, the southeast corner of the state, where rainfall is greatest, has a slightly greater risk—particularly in the native oak woodlands.

    Risk for sudden oak death in the conterminous United States based on agreement between five spatially referenced models (M. Kelly, D. Shaari, Q. Guo and D. Liu, USDA Forest Service General Technical Report PSW-GTR-xxx 2005)

  • Trees at Risk

    Common oaks in Nebraska that are most likely to be susceptible to SOD are in the red oak group (northern red, black, pin, blackjack, shingle, Shumard, scarlet).  The white oak group (bur, white, swamp white, etc) is believed to be less susceptible.

    Plants that may develop Ramorum blight include rhododendron, viburnum, lilac, maple, and magnolia.  California bay laurel is frequently affected in California and Oregon.

    Anyone with a suspected case of SOD or Ramorum blight should contact the University of Nebraska Plant and Pest Diagnostic Clinic:  402-472-2559 or kbroderick2@unl.edu.

  • Links

    California Oak Mortality Task Force:  http://www.suddenoakdeath.org/

    Nursery Guide for Diseases Caused by Phytophthora ramorum on Ornamentals: Diagnosis and Management:  https://anrcatalog.ucanr.edu/pdf/8156.pdf