The new Phytophthora ramorum dynamic in Europe: spread to larch

Sudden oak death (SOD), caused by Phytophthora ramorum, is lethal to tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H. Oh), and threatens this species throughout its range in Oregon. The disease was first discovered in coastal southwest Oregon forests in July 2001. Since then an interagency team has been attempting to eradicate the pathogen through a program of early detection surveys followed by destruction of infected and nearby host plants. Eradication treatments eliminated disease from many infested sites, but the disease continued to spread slowly, predominantly northward, in the direction of winds that prevail during storms and wet weather. During the 10-year period, the disease spread from the initial infestations southward 1.9 km (1.2 mi), and northward and eastward 28 km and 7.6 km (17.3 mi and 4.7 mi), respectively. The area under quarantine has expanded five times, from 22 km² (9 mi2) in 2001 to 505 km² (202 mi2) in early 2012. Continued spread of SOD is attributed to the slow development of symptoms in infected trees which hinders early detection, and to delays in completing eradication treatments due to inconsistent funding. A sharp increase in disease in 2010 and 2011 necessitated major changes to the SOD management program and quarantine regulations.