About Phytophthora ramorum (Sudden Oak Death)

sudden oak deathPhytophthora ramorum (P. ramorum) is a water mold pathogen that causes Sudden Oak Death (SOD). It is also the cause of the Ramorum Leaf Blight, Ramorum Dieback and Phytophthora Canker Diseases.

SOD was first reported in 1995 in Mill Valley (Marin County) on tanoak. It was then observed infecting and killing coastal live oaks, California black oaks, canyon live oaks and Shreve oaks. The pathogen also infects but does not kill a number of other plants.

The California Department of Food and Agriculture has found that SOD presents a clear and present danger to the native stands of oak and other trees, the nursery industry, other agricultural commodities and plant life (including ornamental plantings) of California.

sudden oak deathWhere is P. ramorum?

The disease was confirmed and is currently regulated in 14 counties in California (Alameda, Contra Costa, Humboldt, Lake, Marin, Mendocino, Monterey, Napa, San Francisco, San Mateo, Santa Clara, Santa Cruz, Solano and Sonoma).

How Does P. ramorum Spread?

P. ramorum naturally thrives in cool, wet climates. Significant infections can also occur in plant nurseries that produce plants for these climate conditions. It can spread through wind-blown rain, contaminated irrigation water and infected plants. Soil or potting mix may also spread the pathogen, and it may spread in other ways we do not yet know.

What are the Symptoms of Infection?

sudden oak deathP. ramorum produces three disease symptoms—bark cankers, leaf spots and twig dieback. On oaks and tanoaks, infection that results in tissue death and the formation of calluses on the woody portions of the tree are referred to as cankers. Cankered trees may survive several years. In the final disease stage, the leaves turn from green to brown within a few weeks. Black or reddish ooze often seeps from the cankers. The cankers gradually expand until they girdle the tree, causing it to die. Other diseases cause similar symptoms, so laboratory confirmation is needed for accurate diagnosis.

What Kind of Damage Does P. ramorum Cause?

P. ramorum has a broad range of hosts, including hardwoods, softwoods, landscape plants and herbaceous plants. To date, more than 75 plant species and cultivars representing more than 45 genera can either be infected by P. ramorum or facilitate its spread. Below is a list of proven hosts regulated for P. ramorum:

  • Bay laurel
  • Bigleaf maple
  • California black oak
  • California honeysuckle
  • California maidenhair fern
  • Camellia – all species, hybrids and cultivars
  • Canyon live oak
  • Coast live oak
  • Coast redwood
  • Douglas fir
  • European ash
  • European beech
  • European yew
  • Evergreen huckleberry
  • Horse chestnut
  • Lilac
  • Madrone
  • Manzanita
  • Mountain laurel – all species, hybrids and cultivars
  • Oak, multiple varieties
  • Pepperwood
  • Red tip photinia
  • Rhododendron (including azalea) – all species, hybrids and cultivars
  • Scotch heather
  • Southern red oak
  • Sweet chestnut
  • Tanoak
  • Toyon
  • Vibrunum – all species, hybrids and cultivars
  • Western maidenhair fern
  • Western starflower
  • Witch hazel
  • Wood rose

What Could That Damage Mean to the Economy?

SOD rhodondrenP. ramorum could have major economic implications for the forest, horticultural and small fruit agricultural industries. California is the industry’s leading producer of horticultural plants, valued at $2 billion a year. Regulations restrict shipment of rhododendron and other horticultural host plants from areas where the pathogen is found, greatly impacting the industry. In addition, regulatory actions could also impact the redwood and Douglas-fir industry in California, valued at an estimated $50 million a year.

What Can We Do?

Eradication of the pathogen from nurseries is the best defense against long distance spread. The best defense in eastern oak forests is to prevent its introduction. Early detection through ongoing surveys of nurseries and wildlands is essential. If you suspect that trees or plants are infected with P. ramorum, contact the state department of agriculture.

Resources List

Plant Health
United States Department of Agriculture, Animal and Plant Health Inspection Service
http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/index.shtml

Phytophthora ramorum: Stopping the Spread
United States Department of Agriculture, Animal and Plant Health Inspection Service
http://www.aphis.usda.gov/publications/plant_health/content/printable_version/
SBR_StopTheSpread.pdf

Quarantined and Regulated Counties for Phytophthora ramorum (Map)
United States Department of Agriculture, Animal and Plant Health Inspection Service
http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/pdf_files/
quarantine_jan_05.pdf

Phytophthora ramorum: Pest Risk Assessment
http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/
pdf_files/pra-cphst-11-07.pdf

Phytophthora ramorum: Symptoms
http://www.aphis.usda.gov/plant_health/plant_pest_info/pram/downloads/pdf_files
/phytophthoraramorumsymptoms.pdf

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