Slowing the spread of sudden oak death in Oregon forests, 2001–2018

Sudden Oak Death (SOD), caused by Phytophthora ramorum, is lethal to tanoak (Notholithocarpus densiflorus) and threatens this species throughout its range in Oregon. In July 2001, the disease was first discovered in coastal southwest Oregon forests. Since 2001, an interagency team has been attempting to eradicate and slow the spread of disease through a program of early detection, survey and monitoring, and destruction of infected and nearby host plants. Eradication treatments, totaling approximately 2,550 ha (6,300 ac), eliminated disease from most infested sites, but the disease continued to spread slowly, mostly in a northward direction. From the initial infestations of 2001, the disease has been detected a maximum distance of 30 km (18.5 mi) to the north, 12 km (7.6 mi) to the northeast along the Chetco River, and 15 km (9.3 mi) to the southeast along the Winchuck River. In early 2015, the EU1 clonal lineage of P. ramorum was detected on a single tanoak tree located approximately one mile north of a small private nursery (now closed) near the Pistol River. Genotype comparison of the tanoak and nursery isolates suggests the nursery as the probable source for the forest infestation. This is the first report of the EU1 lineage in US forests. EU1 infested trees have continued to be detected within a small geographic area just north of Pistol River resulting in 190 ha (470 ac) of eradication treatments from 2015 to the end of 2018. In 2017, an Oregon SOD Task Force convened local, state and federal governments and agencies, local tribes, industry associations, and local residents and environmental groups. The mission of the Task Force was to develop a collaborative-based strategic action plan, including securement of additional resources to contain the NA1 pathogen of Phytophthora ramorum and eradicate the EU1 pathogen of Phytophthora ramorum in Curry County, Oregon using the best available science.