Sonoma County Master Gardeners Helping Sonoma Gardeners

 For detailed information and links to UC sites, scroll to the links at the bottom

 

Sudden Oak Death Talks and Preventive Treatment Demonstrations

A group of Master Gardeners have received advanced training in Sudden Oak Death and are conducting talks and preventive treatment demonstration workshops in Sonoma County. Please click here to sign up for a workshop, or a SOD Blitz. A SOD Blitz will educate your community about Sudden Oak Death, enable you to detect disease in your backyard, and result in a detailed map of local disease distribution.

Master Gardeners will also be at Farmers' Markets and talks in the Master Gardener Library Series workshops (see the Calendar).

A talk by Dr. David Rizzo on Sudden Oak Death, click the arrow above to watch the video.  This lecture is an excellent overview of Sudden Oak Death in California. Dave Rizzo's plant pathology lab at UC Davis has been involved in research on Sudden Oak Death since people first noticed tanoaks and oaks dying mysteriously in the SF Bay area in the 1990s. He and his lab played a large role in discovering and naming Phytophthora ramorum, the pathogen that causes the disease, and they continue to research the pathogen. This half-hour talk was presented to a Santa Rosa audience in October, 2007.  Produced by Tola Bein.

 

Sudden Oak Death Overview

Sudden Oak Death is caused by a funguslike pathogen identified by UC scientists as Phytophthora ramorum. The pathogen was also discovered in European nurseries in the mid 1990s, and it has since spread to wildland trees in the U.K. and the Netherlands. Although the first P. ramorum-infested California nursery stock was identified in 2001 in Santa Cruz County, the U.S. nursery industry was not widely impacted by the disease until 2003, when the pathogen was detected in California, Oregon, Washington, and British Columbia nurseries.  Since its appearance Sudden Oak Death (SOD) has killed hundreds of thousands of coast live oak, black oak, tanoak and Shreve oak in northern California. P. ramorum is also the cause of Ramorum blight, which affects the leaves and twigs of numerous other plants in forests and nurseries. It can infect leaves and branches of rhododendron, buckeye, madrone, manzanita, bigleaf maple, bay laurel, and evergreen huckleberry. Two species of East Coast oaks, northern red oak and southern red oak, are also susceptible to P. ramorum.

Possible long term threats include a change in species composition in infested forests and therefore, in ecosystem functioning; loss of food sources for wildlife; a change in fire frequency or intensity; and decreased water quality due to an increase in exposed soil surfaces.

Sudden oak death has been found as far north in the state as Humboldt County and as far south as Big Sur in Monterey County. To date, SOD has been identified in 14 California counties: Alameda, Contra Costa, Humboldt, Lake, Marin, Monterey, Napa, San Francisco, San Mateo, Santa, Clara, Santa Cruz, Sonoma, Mendocino. Solano. In Oregon, Sudden Oak Death has been confirmed in Brookings, a small town in the southwestern corner of the state.

Environment/Habitat
P. ramorum thrives in cool, wet climates. In California, coastal evergreen forests and tanoak/redwood forests within the fog belt are the primary habitat. Research in California forests has shown that the greatest predictor of P. ramorum is the presence of California bay laurel (Umbellularia californica). Nurseries outside of these cool, moist areas often create microclimates which mimic the preferred environment of P. ramorum and allow it to grow and spread far from the coast.

Symptoms
Bleeding or oozing of a dark reddish-brown thick sap is the first symptom to appear on true oaks. It typically occurs on the lower portion of tree trunks (less than 10 feet) but has been found as high as 60 feet. On tanoak, the first symptom is drooping of new growth. Beetles attack weakened trees. Wood decaying fungi are seen in the later stages of decline on the trunks of oaks and tanoaks.

Prevention
Preventing the movement of infected leaves, wood and soil will be critical to slowing the spread of the fungus to other oak woodlands, such as the Sierra Nevada. Plant material and soil should not be moved from coastal areas. Any wood already moved elsewhere should be burned. Visitors to coastal forests should clean their tires, shoes and animals' feet thoroughly before leaving the area. Construction workers should wash equipment well and should not move dirt from one place to another. Ornamental plants, such as rhododendrons, that may be hosts should not be moved from infected counties unless certified to be free of the pathogen.

Treatment
The California Department of Pesticide Regulation approved a special registration for Agri-Fos fungicide in October 2003. It is currently the only chemical treatment approved by the State for use against Phytophthora ramorum infections on oaks and tanoaks. The compound is best used as a preventative measure and is NOT A CURE, but it can help protect trees from getting infected, as well as suppress disease progression in very early infections. Professional arborists, tree-care companies and pest control companies can apply Agri-Fos. It is NOT an inexpensive treatment.      Click here for more treatment details.

Similar Appearing Diseases
Phytophthora cinnamomi can produce identical symptoms in oak trees. Scientists differentiate this fungus from Sudden Oak Death by using a lab test. P. cinnamomi can infect about 1,000 plant species. It can kill oaks, rhododendrons and other nursery plans and agricultural crops including almond, walnut and avocado trees.


The above overview was compiled from information on the UCCE--Sonoma County, and California Oak Mortality Task Force websites. Click the links below for much more detail and information, including diagnosis and sampling, treatments, sanitation and disposal, and  lists of arborists and applicators.