Sudden oak death management in Oregon tanoak forests

Abstract

Sudden oak death (SOD) caused by Phytophthora ramorum was first discovered in Oregon forests in July 2001. There appear to have been three separate introductions of P. ramorum into Oregon; in approximately 1998, and 2014. The most recent of these was the EU1 clonal lineage; all others were the NA1 clonal lineage. Since 2001 an interagency team has been attempting to eradicate the pathogen though a program of early detection (aerial and ground surveys, stream baiting) and destruction (herbicide treatment, felling and burning) of infected and nearby host plants; the program has evolved over time. Post-treatment monitoring indicates that although the pathogen has been eliminated from many of the sites, spread continues. From 2001 to 2015 the quarantine area expanded from 23 km 2 to 1,333 km 2 , where it remains to date. Within a 145 km 2 Generally Infested Area near the center of the quarantine area, most sites have not been treated and the disease has been allowed to intensify and spread. Where eradication treatments have stopped, canopy tanoak mortality increased from nearly zero to 87 percent during the 2012-2016 period. Managing sudden oak death in Oregon forests is challenging for many reasons and Oregon's program is likely to change in the future.

Assessment of the eradication measures applied to Phytophthora ramorum in Irish Larix kaempferi forests

“…40%) of P. ramorum 30 months after eradication measures were applied. Isolation success of P. ramorum from soil and litter has also been shown to decrease over time in eradication treated tanoak forests in Oregon (Goheen, Kanaskie, Hansen, Reeser, & Sutton, ; Goheen et al., ) and in infected Rhododendron leaves buried less than 6 cm below the surface in Californian forests (Fichtner et al., ). Overall, the lack of positive findings from the soil samples in our study is in agreement with the findings of McCracken et al.…”

“…Experience of the effectiveness of eradication measures against P. ramorum in the Pacific Northwest of the USA, and in particular Oregon, is of longer standing. Here, the disease, known as Sudden Oak Death (SOD), and associated eradication efforts have been well documented since the start of the infestation in the early 2000s (COMTF, 2/2014; COMTF, 11/2014; COMTF, 9/2015; COMTF, 6/2016; Goheen, Hansen, Kanaskie, Sutton, & Reeser, ; Goheen et al., , , , , ; Hansen, ; Hansen, Kanaskie, Goheen, Osterbauer, & Sutton, ; Kamvar, Larsen, Kanaskie, Hansen, & Grünwald, ; Kanaskie, ; Kanaskie et al., , , , , ; Peterson, Hansen, & Hulbert, ; Peterson, Hansen, & Kanaskie, ; Peterson et al., ). The aim of the SOD programme in Oregon focuses on eradicating spot infections, before they can become sources of inoculum (Hansen, ).…”

Efficacy of local eradication treatments against the sudden oak death epidemic in Oregon tanoak forests

“…About 80% of new infections are found within 300 m of previously infected trees (Hansen et al, ). The pathogen produces deciduous sporangia on infected leaf and twig tissue primarily of tanoak in Oregon and is regularly recovered from rainwater (Davidson, Patterson, & Rizzo, ; Davidson, Wickland, Patterson, Falk, & Rizzo, ; Hansen et al, ) and from soil (Fichtner, Lynch, & Rizzo, ; Goheen, Kanaskie, Navarro, & Hansen, ; Peterson Hansen & Hulbert, ) beneath infected trees. Umbellularia californica is less common in south‐western Oregon than in California and is less frequently infected.…”

“…As SOD continued to spread, the quarantine area was expanded; in 2017, it covered 1,333 km 2 . An early detection survey and local eradication programme was initiated in 2001, relying on aerial survey to locate recently killed trees with red crowns and ground checking with verification by direct isolation or PCR (Winton & Hansen, ) to confirm new infestations, and cutting and burning diseased tanoak trees and associated host plants (Goheen et al, , ; Kanaskie et al, ). The eradication treatment has evolved through time as new information became available.…”

“…Despite the sustained effort, the pathogen continues to spread in Curry County, and in 2017, a new infestation of the EU1 lineage started to spread. In 2012, the goal of the programme was restated from “eradication” to “slow the spread” (Goheen et al, ).…”