Sudden Oak Death
From Bugwoodwiki
Georgia Forestry Commission Forest Health Monitoring Factsheets
Written by Terry Price, Georgia Forestry Commission
Adapted for the web by the Bugwood Network
(Phytophthora ramorum)
Contents |
History and Current Distribution
A newly identified foreign pathogen threatens Georgia's oak woodlands. Sudden oak death is caused by the fungus P. ramorum. This pathogen has existed in Europe for many years and was probably introduced into California in the early 1990's. By 1995, oak trees began dying in California and eventually the pathogen causing sudden oak death was confirmed as the causal agent. So far, the disease has spread to 14 California counties, as well as Oregon's Curry County. Tens of thousands of coast live oak, tanoak and California black oak trees have been killed.
This disease could have severe economic and environmental impacts if it reaches Georgia. Georgia's red and white oaks could be hit hard with this pathogen.
Symptoms
Although the name sudden oak death implies a rapid decline, trees actually die over a period of months to years. The fungus as we know it today first attacks the leaves of plants growing beneath oak trees such as mountain laurel, camellia, rhododendron and viburnum. The understory plants develop leaf spots and blights that serve as sources of spores that can eventually infect trees. The spores that are produced on the understory plants (foliar hosts) are windblown or splashed by rain onto the bark of oak trees where they eventually penetrate the living tissues of the tree. Trees that are attacked by the fungus develop cankers under the bark that eventually girdle and kill the tree, which often takes two years or more.
Figure 1 shows leaf infections on rhododendron.
Scientists working with this disease have identified numerous foliar hosts that may contribute to the spread of the fungus. Included in this growing list of plants are: camellia, rhododendron, azalea, viburnum, mountain laurel, honeysuckle and lilac.
 Photo by Joseph O'Brien, USDA Forest Service, Bugwood.org Figure 1 |
Long Distance Spread from California
Three west coast nurseries have been identified has having infected plants. In March of 2004, plants from a Monrovia nursery in California were identified as being infected with the pathogen. Unknowingly, Georgia nurseries had been receiving thousands of potentially infected plants from this nursery since January of 2002. This same nursery had shipped plants throughout the eastern U.S. Since October of 2004 two additional nurseries in Oregon (Hines and Means) have been identified as having shipped plants into Georgia that could have been infected with the pathogen.
What Has Been Done To Date
State and federal officials throughout the U.S. have established quarantines to prevent further shipments of infected plants into their states. Georgia had already organized the Sudden Oak Death Advisory Committee (SODAC) in early 2003 (prior to the Monrovia incident) and had begun a systematic survey of forests and nurseries in partnership with the U.S. Forest Service and other state departments of agriculture and forestry to determine if the disease was already present. Later when the Monrovia nursery connection was learned, efforts by SODAC were redirected to specific nursery shipments coming into Georgia from the Monrovia nursery. To date, sudden oak death has not been detected in Georgia's oaks. The fungus has been found in nursery plants that have been out planted into yards across the State and these plants have been destroyed.
What Can You Do To Help
There is still time to prevent the disease from escaping into the oaks of Georgia, but your prompt action is needed. If you bought Monrovia nursery plants anytime after January 2002 you may have received some infected plants. Monrovia plants can be identified by the distinctive green plastic pot with the name Monrovia printed on the side (Figure 2). Also, Monrovia plants are tagged with a very attractive color photo of the plant with the name Monrovia prominently displayed (Figure 3). The other two west coast nurseries that have shipped plants into Georgia that may have been infected with the pathogen use regular pots with no distinct names or markings on them. If you have purchased camellias, rhododendrons, azaleas etc. you should ask the nursery where you purchased the plants if they or any of their brokers deal with the Hines or Means nurseries in Oregon.
For further information concerning sudden oak death, contact your local Georgia Forestry Commission or County Extension Agent office.
