Treesearch

The primary foliar host for Phytophthora ramorum is California bay laurel, Umbellularia californica (Hook. & Arn.) Nutt., a main reservoir for the pathogen in California woodlands. We investigated environmental and pathogen-mediated influences on incidence and severity of P. ramorum infection of U. californica, as well as developing non-destructive means for controlling P. ramorum in woodlands.

The Big Sur region of central California is a rugged, fire-prone area that has been severely affected by Phytophthora ramorum. Meentemeyer et al. (2008) estimated that over 200,000 oaks and tanoaks had been killed by P. ramorum across the Big Sur ecoregion by 2005. In June of 2008, a complex of lightning-initiated fires burned over 95,000 ha in Big Sur, including 43 percent of our long-term network of disease monitoring plots. Here we compile data collected in these plots before the fire in 2006 and 2007 (Metz et al. 2011), with 3 consecutive years of data following the fire (2009 through...

Germination of chlamydospores is difficult to accurately assess when chlamydospores are attached to remnants of supporting hyphae. We developed two approaches for closely observing and rigorously quantifying the frequency of chlamydospore germination in vitro. The plate marking and scanning method was useful for quantifying germination of large numbers of chlamydospores over a 7-day period. A method involving time lapse photography of microscope slide cultures was effective for visualizing the process of germination over shorter time periods.

In California, wildland hosts that support sporulation of Phytophthora ramorum, such as California bay laurel (Umbellularia californica (Hook. & Arn.) Nutt.) and tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H. Oh), also develop prolific basal sprouts following mortality, injury, or tree harvest. Assessing long-term silvicultural treatment effectiveness for P. ramorum control is complicated by this stimulation of basal sprouting following tree removals. To better design P. ramorum treatments, we need to know how sprouts regenerating from cut host tree stumps are...

We are working to evaluate risks associated with human spread of the sudden oak death (SOD) pathogen, Phytophthora ramorum, to currently uninfested areas in California. Port-Orford-cedar (Chamaecyparis lawsoniana (A. Murray) Parl.) root disease (POC RD), caused by Phytophthora lateralis, has brought awareness that pathogens can be moved in forest settings by materials adherent to vehicles and equipment. Discovery of this human vector prompted P. lateralis control measures with notable social and economic costs, such as road closures, vehicle and equipment washing requirements, and standards...

Phytophthora ramorum, the cause of sudden oak death, was first discovered in Oregon forests in July 2001. An aggressive eradication treatment program was immediately put into place on all lands where it was found. Eradication treatments have changed over time as we have learned more about pathogen behavior. Treatment prescriptions currently consist of cutting and burning infected and exposed host plants, and where possible, injecting herbicide into tanoaks to prevent sprouting. The effort has slowed, but not stopped, long-distance dispersal of the pathogen.

Sudden oak death, caused by the invasive oomycete pathogen Phytophthora ramorum, continues to shape the dynamics of coastal populations of oak (Quercus spp.) and tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H. Oh) in California and tanoak in southwestern Oregon. Over the last decade, high mortality rates have been reported in natural populations of coast live oak (CLO; Quercus agrifolia Née) in California, raising concerns for the integrity of important coastal ecosystems. However, it is now recognized that in spite of high infection and mortality rates, asymptomati...

Phytophthora ramorum-infested soils have been implicated as a source of primary inoculum in natural ecosystems. Implicit in this pathway is the need for infection of understory vegetation during pathogen establishment, preceding infection of bole hosts. In support of soil dispersal, studies using artificiallyinoculated soils have shown that understory inoculum can infect low-lying foliage of tanoak (Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H. Oh) and California bay laurel (Umbellularia californica (Hook. & Arn.) Nutt.) (Fichtner et al. 2009). The lack of association...

The Marin Municipal Water District's (MMWD) 7487 ha Mt. Tamalpais watershed in Marin County, California has the dubious distinction of being one of the earliest and most extensive areas impacted by Phytophthora ramorum in California. Rapid die off of tanoaks (Notholithocarpus densiflorus (Hook. & Arn.) Manos, Cannon & S.H. Oh) were first documented in 1995.With funding support from the U.S. Department of Agriculture Forest Service, MMWD initiated an assessment of landscape-scale changes in forest structure and understory floristics relative to P. ramorum spread in the Mt Tamalpais watershed...

With its high host mortality and ability to cause landscape-scale alterations in forest cover and composition, sudden oak death (SOD) (etiological agent Phytophthora ramorum, Stramenopila, Oomycota) mirrors past forest disease epidemics such as Chestnut Blight and Dutch Elm Disease. In contrast with these past epidemics, however, the appearance of SOD converges with a time of significant advancement in the development of molecular genetic tools that allow the movement of individuals (or individual genotypes) to be tracked and the role of evolutionary processes in disease progression to be...