sudden oak death Phytophthoraramorum S. Werres, A.W.A.M. de Cock
Origin
A foreign pathogen threatens Georgia's oak woodlands. Sudden oak death is caused by the fungus-like 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.
Life Cycle
Although the name sudden oak death implies a rapid decline, trees actually die over a period of months to years. The pathogen 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-like pathogen develop cankers under the bark that eventually girdle and kill the tree, which often takes two years or more.
Distribution
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. 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.
Control Efforts
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 pathogen has been found in nursery plants that have been out planted into yards across the State and these plants have been destroyed.