Treesearch

Phytophthora ramorum is an oomycete pathogen and causal agent of a disease commonly referred to as sudden oak death (SOD). The pathogen also causes foliar blight and shoot dieback of nursery plants, including Rhododendron and Viburnum. It is responsible for the widespread mortality of tanoak (Notholithocarpus densiflorus) and coast live oak (Quercus agrifolia) in coastal California and southwestern Oregon, as well as Japanese larch (Larix kaempferi) in the U.K. Thirty-three plant host species commonly found in eastern (8) and western (25) Canadian landscapes and forest sites were selected...

Phytophthora ramorum, the cause of Sudden Oak Death (SOD), is an oomycete pathogen that has invaded coastal California and southern Oregon mixed-hardwood forests. In southern Oregon forests, tanoak (Notholithocarpus densiflorus) is the most susceptible species developing lethal stem cankers and sporulating from infected leaves and branches. Two lineages (NA1 and EU1) of P. ramorum occur in Oregon forests. The first step in a successful tanoak breeding program is to determine if variation in resistance to these two lineages exists. The objectives of this study are to: (i) characterize the...

In California, leaves of California bay laurel (Umbellularia californica) are considered the primary naturalized source of inoculum for the devastating forest disease sudden oak death (caused by Phytophthora ramorum), and yet this plant and insects associated with its leaves remain understudied. Previous studies have considered the role of insects as synergistic factors on trees that die of P. ramorum such as oaks, but none have related disease prevalence to insect presence on bay laurel. Indeed, joint effects of insects and pathogens on plants have been investigated surprisingly rarely,...

Sonoma County has more sudden oak death (SOD) than any other county in California and the disease is still spreading. At least 163,000 acres of Sonoma County’s forests are affected by SOD based on USDA Forest Service aerial surveys, and tanoak (Notholithocarpus densiflorus) deaths attributed to the disease in the Northern California Shared Service Area increased almost eightfold between 2016-2017. SOD Blitz data showed a nine-fold increase in estimated true infection rate of trees in some areas of Sonoma County from 2015-2017 and new outbreaks continued to appear in 2018. Thanks to funding...

Surveys of native wildlands worldwide to determine Phytophthora diversity have found a surprisingly large assortment of root disease-causing species, many of which may contribute to the phenomenon of oak decline. Many species of concern, for example P. cinnamomi, are widely distributed throughout the San Francisco Bay Area. Others, notably P. quercina and P. uliginosa, may additionally contribute to oak decline in Europe (Jung and others 1999, 2002), but are not thought to be widely distributed in the western United States. To determine Phytophthora diversity and distribution in the...

Lake Mathews is a 182,000 acre-feet capacity reservoir located in Riverside County, California. It is the western terminus of the Colorado River Aqueduct that serves as the main source of irrigation water for several horticultural nurseries in southern California. Some of these nurseries do not disinfest Lake Mathews water before using it for irrigation. This could increase disease pressure at these nurseries and facilitate survival, propagation and spread of important waterborne plant pathogens such as Phytophthora spp. on infested nursery stock. We examined the diversity of Phytophthora...

Since its introduction into California, Phytophthora ramorum was found predominately on a rather narrow band along the coast characterized by mild temperatures and abundant year-long moisture (in the ‘fog belt’). The presence of foliar hosts, especially California bay laurel (Umbellularia californica), common in this ecosystem, is an essential driver for the spread of the disease to ‘dead-end hosts’, such as coast live oak (Quercus agrifolia). Recently, P. ramorum was detected on several plants typical for the chaparral plant community (manzanita, Arctostaphylos spp.; chaparral pea,...

During a series of large riparian restoration projects in the San Francisco Bay Area, Phytophthoras on infected planting stock were inadvertently introduced into a number of sites. There are many planting basins at some of these sites where hosts from a nursery that had a high rate of Phytophthora positives were planted. These basins are scheduled for treatment once a potential mitigation approach to kill any introduced Phytophthoras is decided upon. Steaming has been shown to be an effective mitigation treatment to eliminate Phytophthoras from infested soil. In nursery and landscape sites...

Understanding the impacts of disease and fire on forested ecosystems is a major challenge facing scientists, land managers, policy makers and landowners. Due to difficulty in predicting wildfire, few studies of ecological effects of fire are based on both pre- and post-fire data. The goal of our research is to use a large scale and long-term plot network with both pre- and post-fire data in eastern Sonoma County to determine the ecological impacts of an exotic pathogen (Phytophthora ramorum) and wildfire on oak-woodland forest communities. We aim to answer the following questions: 1) Do...

Phytophthora ramorum, causal agent of sudden oak death, continues to threaten U.S. forest ecosystems and the nursery industry. Currently, USDA APHIS’s protocol (2014) utilizes the Bottle of Bait (BOB) recovery method for P. ramorum, which requires collecting water from a source, baiting with healthy rhododendron leaves for a 3-day incubation period, followed by plating on semi-selective media. Rapid methods are needed for recovery and detection of P. ramorum propagules from water sources. Working at the National Ornamentals Research Site at Dominican University of California (NORS-DUC), we...