Plant Industry - Sudden Oak Death (SOD)
Ramorum Leaf Blight, Ramorum Dieback - a nursery plant disease that threatens oaks
Sudden Oak Death (SOD), ramorum leaf blight and ramorum dieback are all names for a recently-discovered plant disease caused by the fungus-like microorganism Phytophthora ramorum. It has killed thousands of oak trees in California and Oregon in the past decade. More information is provided at the following website: USDA-APHIS-PPQ Phytophthora ramorum/Sudden Oak Death, the California Oak Mortality Task Force (COMTF), and the North Central IPM Center and PRED Program.
Although some eastern-U.S. oak species are highly-susceptible to SOD, the disease is not known to be established in landscapes, natural areas, or forests in States other than California and Oregon (as of 7/1/2023). However, since 2004, it has been detected on ornamental nursery plants in many States, primarily in connection with infected plants moving in the nursery trade from the west coast. The known host range of is very broad and includes commonly-grown ornamental plants like camellia, viburnum, pieris, rhododendron, and many others. Although SOD does not usually kill these non-tree hosts, it causes symptoms such as leaf-spots, defoliation, twig and branch dieback, or blighting that can easily be confused with symptoms caused by other plant diseases or environmental stresses. Infected plants can easily escape detection. Laboratory analyses are necessary to confirm the presence of SOD in all cases.
NCDA&CS is concerned about the possible introduction of SOD into North Carolina on ornamental plants. Nurseries and nursery dealers often buy-in ornamental plants from other States where Pram is known to occur. Despite the federal quarantine requirements intended to prevent the movement of the disease into other parts of the U.S. on infected plants, the measures are not 100% effective. Infected plants could still be shipped into NC, purchased by a homeowner or landscaper, and planted in the landscape where the disease could become established. From there, it could move into the larger environment and adversely impact our oaks and other trees. This is why NCDA&CS continues to survey and monitor plants in nurseries and nursery dealers on a routine basis for symptoms of SOD.
Activities in North Carolina
The first detection of SOD in a nursery in NC occurred in 2004. Those plants were destroyed. Based on subsequent surveys conducted by NCDA&CS and NC Forest Service personnel, SOD did not spread within the nurseries onto other plants nor become established in the surrounding natural areas surrounding the nurseries. NCDA&CS continued its participation in the national survey of nursery and nursery dealers and handled additional “trace-forward” investigations.
Most recent detection was in June 2020. Rhododendron plants purchased from an on-line retail store based in Oregon with suspicious symptoms of Phytophthora ramorum infection were found at a newly established certified nursery. Upon receiving the confirmation result, NCDA&CS took immediate regulatory actions according to USDA protocols. All plants within 2-meter radius of the positive plant were destroyed; all plants within 4-meter radius were held for further inspection. The greenhouse floor and benches were disinfected with 10% bleach. All plants that were received from the same shipment were carefully inspected for symptoms. A comprehensive delimiting survey at the nursery for all the plants on the USDA official host list was done. No additional positive case was detected at the nursery. Water sampling and stream bait sampling was done to make sure the pathogen did not spread into the surrounding natural area. Two follow-up inspections of the plants being held were conducted within 90 days. No additional symptomatic plant was found, and all plants were released.
Locations of the most recent annual survey at nursery and nursery dealers are shown in the maps below.
North Carolina remains free of Phytophthora ramorum
