Long-term trends in coast live oak and tanoak stands affected by Phytophthora ramorum canker (sudden oak death)
2000-2010 Disease Progress Update
T. J. Swiecki and E. A. Bernhardt
Phytosphere Research, Vacaville CA
email: phytosphere@phytosphere.com
We collected data in our 150 long-term sudden oak death (SOD) monitoring plots in Marin, Napa, and Sonoma counties in September and October 2010. Evaluations were somewhat appreviated compared with plot evaluations conducted through 2007 due to reduced funding available for this project. In 2010, we evaluated:
-
current Phytophthora ramorum disease status;
- disease status due to other agents;
- the occurrence and characteristics of new failures.
As shown in the figures below, the number of infected tanoaks increased slightly in 2010, but there was no net change in disease incidence in coast live oak. SOD symptoms have been seen in more than half of all tanoak trees in our study plots as of 2010, and about 38.6% of all tanoaks in the plots had been killed by SOD through 2010. In contrast, only about a third of coast live oaks in the plots have developed SOD symptoms. Mortality due to SOD in coast live oak was 16.5% through 2010. For both species, rates of mortality due to factors other than SOD remain relatively low, but background levels of mortality are greater for coast live oak than tanoak.
Monitoring data will be collected in September and October 2011. The 2011 data will provide the first indication of whether SOD levels in susceptible oaks and tanoaks have increased as a result of the wet spring conditions (favorable for new P. ramorum infections) seen in 2010 and 2011. However, many of the new infections initiated in 2011 may not be visible until 2012.
Figure 1. Status of coast live oaks in SOD-affected stands from 2000 through 2010. Asymptomatic=live trees without SOD symptoms or severe decline due to other factors, All Pr=trees with SOD symtoms (live or dead), Other decline=trees declining due to factors other than SOD, Other dead=trees dead due to factors other than SOD.
Figure 2. Status of tanoaks in SOD-affected stands from 2000 through 2010. Asymptomatic=live trees without SOD symptoms or severe decline due to other factors, All Pr=trees with SOD symtoms (live or dead), Other decline=trees declining due to factors other than SOD, Other dead=trees dead due to factors other than SOD.
