New strain of Sudden Oak Death detected in small number of trees in northern Curry County
CURRY COUNTY -- An infestation of the European strain (EU1) of P. ramorum, the causal agent of Sudden Oak Death, has been discovered in 12 tanoak trees and one grand fir seedling in the Curry County wildlands, Oregon Dept. of Forestry officials said.
Testing results are still pending for another grand fir tree and 11 tanoaks. No infestations of the EU1 strain have been found in Douglas fir trees in the area, officials said.
Certain species of oak commonly found in Oregon, including tanoak and California black oak, are highly susceptible to and more likely to die from the disease. Though firs can be affected by SOD, the disease damages new shoots and twigs when growing near heavily infested tanoak and does not appear to kill mature firs.
Like the North American (NA1) strain, the EU1 strain spreads mostly by air when rain splashes spores into the wind, which carries them to another host species. People can also spread the disease by transporting infected plant material to uninfected areas, officials explained.
In early 2015, the EU1 strain was detected for the first time on a single tanoak near the Pistol River. This is the first report of the EU1 lineage in US forests. Officials say genetic analysis suggests a nearby private nursery, which is now closed, as the probable source.
In August of this year, a second EU1 infestation was detected between the 2015 site and a now closed ornamental nursery. The new EU1 find came following the detection of a EU1-positive stream sample near Pistol River.
The Department of Forestry is working with Oregon State University to determine how aggressive Oregon's EU1 strain is. OSU is evaluating the relative threat of EU1 and NA1 lineages of P. ramorum to common West Coast forest tree species of Douglas fir, tanoak, Oregon white oak, western hemlock, Sitka spruce, and madrone by inoculating these species with each strain.
Logs of each species will be inoculated to compare the development of stem lesions. In the United Kingdom, the EU1 strain prolifically produces spores on Japanese larch and leads to dieback of nearby conifer species, such as Douglas fir. A second experiment is planned to measure relative spore growth rates of EU1 and NA1 from the leaves and needles of the six West Coast tree species.
"At this time no Douglas fir are affected, however it is good for people to be aware of the new strain" said Sarah Navarro, ODF forest pathologist. "Though the infestation is limited within one area and not widespread, it is the furthest northern infestation of sudden oak death found in Curry County and is a high priority issue for ODF."
ODF is working with the Oregon Department of Agriculture and other agencies to prioritize treatment. A 300- to 600-foot buffer boundary has been established to treat the area.
Equally important to the treatment of SOD is preventing spread of the disease, officials said. South coast landowners are reminded of the state quarantine, which has been in effect since the first detection in 2001. The quarantine prohibits harvest of host material (tanoak) from known infested areas within the quarantine area. This includes restrictions on the commercial sale of tanoak firewood from within the quarantine area. The rules also apply to soil and plant debris that could be contaminated by the pathogen.
Currently, the approximate boundary starts at the mouth of the Rogue River in the north, then extends east to Pebble Hill, then south to the Big Craggies, then east to Granite Butte, then south to the California border, and then west to the Pacific Ocean. A map showing the exact boundaries is available at http://go.usa.gov/xKzRd.
For more information on P. ramorum and the Curry County quarantine contact the Oregon Department of Agriculture at 503-986-4559 or go visit http://www.oregon.gov/ODA/programs/NurseryChristmasTree/Pages/SOD.aspx