Treesearch

Diseases caused by Phytophthora ramorum in forest landscapes of North America are presently confined to areas of the Pacific coast in the states of CA and OR. However, the vulnerability of other ecosystems is suggested by the discovery in Europe and the U.K. of disease in hosts which are abundant in oak-dominated ecosystems of eastern North America; successful greenhouse inoculation trials of these and other potential eastern tree and shrub hosts; and brisk domestic and international trade in woody ornamental hosts. Overlay analysis was used to project low, moderate or high risk of P....

Phytophthora ramorum was found for the first time in the Netherlands in 1993. In 2001 a risk analysis was done. The results initiated a program to investigate the spread in the Netherlands and to develop measures to prevent further spread. The measures outside the nurseries gave rise to intensive discussions with the managers and owners of these areas. In 2002 the European Union (E.U.) Commission Decision aimed at preventing introduction and spread of the pathogen and gaining insight in the distribution came into force. During the first season of inspections 4 percent of the nurseries...

Understanding the impacts of Phytophthora ramorum on forests will require knowledge of pre-disease distribution, abundance, and rates of change for affected species. This study estimated pre-epidemic mortality rates for nine common host tree species: bigleaf maple (Acer macrophyllum), California bay laurel (Umbellularia californica), California black oak (Quercus kelloggii), canyon live oak (Quercus chrysolepis), coast live oak (Quercus agrifolia), Douglas-fir (Pseudotsuga menziesii), madrone (Arbutus menziesii), coastal redwood (Sequoia sempervirens), and tanoak (Lithocarpus densiflorus)...

In March 2000, we established twenty disease progression plots in Marin County to monitor the progress of sudden oak death symptoms in coast live oak (Quercus agrifolia), California black oak (Q. kelloggii), and tanoak (Lithocarpus densiflorus) (McPherson and others 2005). Plots were located to encompass a variety of habitat types and species combinations, ten in China Camp State Park and ten in Marin Municipal Water District. We monitored every coast live oak (731), California black oak (52), and tanoak (181) with a stem diameter greater than 2.5 cm, four times a year. Trees were evaluated...

This paper reports on five years of observations in a case-control study examining the role of tree and site factors on the development of Phytophthora ramorum stem canker (sudden oak death) in coast live oak (Quercus agrifolia) and tanoak (Lithocarpus densiflorus). In September of each year from 2000 through 2004, we collected data on P. ramorum symptoms, tree condition, midday stem water potential (SWP), and various other factors in 150 circular plots (8 m radius). Each plot was centered around a case (symptomatic) or control (asymptomatic) plot center tree. Plots were located at 12...

Phytophthora ramorum, the causal agent of sudden oak death, was first discovered in Oregon in July 2001 by aerial survey (Goheen and others 2002). Alerted to the situation in California and experienced in aerial tree mortality surveys, cooperators from the USDA Forest Service and the Oregon Department of Forestry planned a pilot survey for P. ramorum to become familiar with what was perceived to be the high risk type: forest stands with tanoak components within approximately 16 km of the Oregon coastline and along highly traveled road corridors leading to and from California. One hundred...

Phytophthora ramorum, while thought to be primarily an aerial pathogen, can be introduced into soilless potting media in the nursery industry as sporangia or chlamydospores and be disseminated widely without being detected. Inoculum of this pathogen, both North American (A2) and European (A1) isolates were used to infest potting media components or soil as sporangia or chlamydospores produced in vermiculite culture or in infected rhododendron leaves. Vermiculite chlamydospore/oospore inoculum of P. citricola, P. cactorum, and P. citrophthora were included for comparison. Survival was...

A range of fungicides have been tested for activity against P. ramorum using both in vitro and in vivo tests. All fungicides had proven activity against Phytophthora species and either had full approval for use on hardy ornamental nursery stock in the United Kingdom, or could be used under the Revised Long Term Arrangements for Extension of Use (2002). Fungicides were initially tested for in vitro activity against mycelial growth and spore germination of two isolates of P. ramorum from the U.K. Agar plate tests showed that metalaxyl-M (SL 567A), dimethomorph/mancozeb (Invader), etridiazole...

As the name implies, sudden oak death, caused by Phytophthora ramorum, kills many, if not most of the coast live oaks, Quercus agrifolia, that become infected (McPherson and others, 2005). Several genera of ambrosia and bark beetles (Coleoptera: Scolytidae) colonize bleeding (infected) trees and are suspected to hasten tree death. Insecticide treatment is being offered to property owners to prevent the death of high value trees, although controlled studies of its efficacy are lacking. In this study, we are testing the efficacy of the synthetic pyrethroid insecticide permethrin in prolonging...

In May 2003, a Phytophthora ramorum infested garden in the surroundings of Nijmegen, the Netherlands, was cleared of infected Rhododendron shrubs by cutting the plants back at 30 cm. In an experiment the remaining parts of the Rhododendron plants were treated with thiophanate–methyl, glyphosate or untreated. In the same experiment, the effect of additional phytosanitary measures, removal of plant debris and humus or plant debris only, was tested. The re-growth and occurrence of new infections were monitored. Soil samples were taken monthly at 20 cm depth or at soil surface and tested for...