Treesearch

The summer of 2008 brought the first wildfires to occur in known Phytophthora ramorum-infested forests in California, with the largest individual fire burning in the Big Sur region of the central coast (Monterey County) (Metz et al. 2011). More than 100,000 ha in Big Sur were ultimately burned that summer, providing a natural experiment to examine the feedbacks between a destructive, invasive forest pathogen and wildfire. Big Sur is one of the most botanically and ecologically diverse areas in California, and its forests were among the earliest infested and most impacted by sudden oak...

Invading species can alter ecosystems by impacting the frequency, severity, and consequences of endemic disturbance regimes (Mack and D'Antonio 1998). Phytophthora ramorum, the causal agent of the emergent disease sudden oak death (SOD), is an invasive pathogen causing widespread tree mortality in coastal forests of California and Oregon. In the absence of the pathogen, species composition in these forests is shaped by a number of biotic and abiotic factors, including wildfire. Large wildfires in California in 2008 provided an opportunity to test the interactions between P. ramorum and...

Sudden oak death has impacted forests notable for high-fire risk and contiguous host communities in California and Oregon coastal forest ecosystems. The disease continues to emerge in stands and landscapes with a large biomass of tanoak (Notholithocarpus densiflorus (Hook.&Arn.) Manos, Cannon & S.H.Oh), and we show that woody debris also increases with the progression of disease. This increase in fuels and the possibility of increased carbon release may impact wildfire intensity, wildlife, and regional carbon management goals (Cobb et al. 2012a, Lamsal et al. 2011, Valachovic et al. 2011).

Although it has been convincingly shown that forest populations of the pathogen Phytophthora ramorum have undergone a significant bottleneck and reproduce exclusively asexually (Ivors et al. 2004, 2006; Mascheretti et al. 2008), objective results showing that nurseries were the original source of the introduction remain elusive (Mascheretti et al. 2008). A previous attempt to define routes of pathogen movement resulted in a largely unresolved network (Mascheretti et al. 2009), showing at best that populations from Santa Cruz and Marin Counties were important sources within California....

Many Phytophthora species, including Phytophthora ramorum, have been reported from surface waters such as canals, streams, rivers, ponds, and reservoirs, often in association with infested agricultural or natural landscapes (Hong and Moorman 2005). Phytophthora species are recovered with regularity and abundance from streams and rivers, in many cases in the absence of apparent terrestrial infestations (Hwang et al. 2010, Reeser et al. 2011, Sutton et al. 2009), or under conditions not conducive to sporulation in the landscape in the case of California summers. This strongly suggests that...

In situ baiting with whole, intact leaves of Rhododendron spp. has been employed since 2006 by the National Phytophthora ramorum Early Detection survey of forests (national survey). Using this method, P. ramorum was detected for the first time in national survey waterways draining 12 infested ornamental crop nurseries in Alabama, Florida, Georgia, Mississippi, North Carolina, and Washington as well as many forest areas in California and Oregon. In situ baiting periods lasting 1 to 3 weeks allow sampling large volumes of water over time, but also can result in loss of bait leaves from storm...

European phytosanitary measures as applied to nurseries require that potential host plants within a radius of 2 m of a Phytophthora ramorum-infected plant must be destroyed and that remaining host plants within a radius of 10 m cannot be traded until they are inspected and found to be pest free at further specific inspections. Despite the wide application and acceptance of these distances, they are not based on data regarding the in-field spread of this pathogen. Our previous study reported at the Fourth Sudden Oak Death Science Symposium demonstrated that direct aerial spread between...

In this study, viburnum (Viburnum) cuttings were treated with oomatistats (Subdue Maxx®, Banol®, and Aliette®) at standard rates for use as soil drenches or with biological control organisms (Streptomyces lydicus formulated as Actinovate SP® and used as a soil drench, and Trichoderma asperellum formulated in wheat bran and used as a top dressing) 4 days after roots were infected with Phytophthora ramorum. The amount of inoculum in runoff samples taken weekly for 5 weeks was studied using a quantitative assay analyzed as a mixed model regression and the percent colonization of roots at the...

Phytophthora ramorum, the fungus-like pathogen which causes sudden oak death, is a threat to the Pacific Northwest nursery industry. Because this is a quarantine organism, the destruction of plants and mitigation treatments resulting from a positive P. ramorum detection has caused millions of dollars in losses to the commercial nursery industry in California, Oregon, and Washington. There is concern about movement of the pathogen to nurseries and forests in the eastern United States. An increase has been seen in the NA2 and EU1 lineages from nursery samples in Washington in recent years,...

In most parts of Europe, rhododendron is the most important host for the spread of Phytophthora ramorum. To get a better knowledge of leaf infection and capacity for sporulation, infection studies were carried out. Detached leaves of the Rhododendron cultivar 'Catawbiense Grandiflorum' (CG) and the R. insigne hybrid `Brigitte´ (B) were inoculated with a zoospore suspension of a P. ramorum isolate of mating type A1 and A2, respectively. The CG developed much greater leaf necrosis than B (average after 55 days 106.5 mm2 versus 0.12 mm2). The trichomes on the B leaves seemed to prevent the...