Information on Tanoak -- Sudden Oak Death, An Online Guide to Plant Disease Control, Oregon State University

Pacific Northwest 1998 An Online Guide to Plant Disease Control

Tanoak (Lithocarpus sp.) -- Sudden Oak Death

Cause: A funguslike organism, Phytophthora ramorum, has been found killing tanoaks, wild rhododendrons, and evergreen huckleberry in a few isolated spots just north of Brookings, OR, during the summer of 2001. There was also incidental leaf infection on salmonberry, cascara, myrtlewood, and poison oak (stem cankers). Eradication of infected plants began soon after the sites were found. The infestation has spread slowly in Oregon from isolated spots. The area of new infested sites and expansions of previous infestations includes many acres of forest land near Brookings. Federal and international quarantines have been established to prevent the spread of this pathogen in soil and infected plant material.

The disease was first reported in 1995 in Mill Valley, CA. Since, many oaks have died throughout the central coastal counties of California. Dying trees have been observed in urban and rural forests and woodlands.

The host list for this organism includes many different plants. Several plant species are associated with this organism but are not currently regulated pending experimental confirmation. Tip dieback and/or leaf spotting occurs on bigleaf maple, cascara, coast redwood, Douglas fir, honeysuckle, horsechestnut, huckleberry, kinnikinnick, myrtlewood, Pacific madrone, poison-oak (stem cankers), rhododendron cultivars, salmonberry, Viburnum and others. The disease can be a problem on black oak (Quercus kelloggii), coast live oak (Q. agrifolia), Shreve’s oak (Q. parvula var shrevei), and tanoak (Lithocarpus densiflorus). Laboratory tests indicate that many plant species, both wild and cultivated, are potentially susceptible. Oregon white oak (Quercus garryanna) does not appear to be very susceptible when challenged with the pathogen in lab tests.

Phytophthora ramorum is a fungus-like organism well-adapted to the cool, wet conditions of the PNW and tolerant of heat and drought. Several spore types are produced that help this organism survive and spread. Spores landing on wet leaves or stems germinate and infect the plant. Young leaves are especially susceptible. Within a few days, sporangia are produced which release tiny swimming spores (zoospores). The sporangia themselves can also detach, germinate, and infect. Sporangia and zoospores can be moved with wind-borne rain, irrigation water, or with water splashed onto foliage. Infected myrtle leaves are a major source of spores in the forest. There are two mating types, designated A1 and A2. The forest isolates from California and Oregon are the A2 mating type, while the European isolates are mainly the A1 mating type. Both mating types have been isolated from Oregon nurseries.

Symptoms: Tanoak (and oak) trees appear to die rapidly, turning from an apparently healthy green to brown within a few weeks. Leaves may at first have a darkened petiole. Dead leaves may remain on trees for up to 1 year after tree death. The disease is characterized by brown or black discolored patches of bark on the lower trunk with an exudation of viscous sap from the bark. Bleeding usually is aboveground within 3 to 15 ft of the soil line. A sunken or flattened area may be observed below the bark. A distinctive dark reddish canker margin can be seen in the bark and wood. (Many other Phytophthora species can also cause similar cankers on tanoak.) The new growth on young tanoaks may first look wilty or droopy. Bleeding is not always observed on infected tanoaks particularly if their stem diameters are small. Young stump sprouts from infected trees may have necrotic stems and infected leaves.

The typical symptom on myrtle is black leaf tips, usually with a chlorotic halo. An infected madrone will show leaf spots and tip dieback, although these symptoms are not distinctive. Symptoms on manzanita resemble those on madrone. The symptom observed on bigleaf maple is a leaf spot with a diffuse edge. Darkened stem cankers are on evergreen huckleberry. Tissues above the cankers typically die back. In severe cases, the entire aboveground portion of an infected huckleberry plant may be killed.

If you suspect you have seen a P. ramorum-infected plant in Oregon, call the Invasive Species Hotline, 1-800-INVADER (1-800-468-2337).

The first occurrance of Sudden Oak Death in Oregon was on these Tanoak trees. Note the brown trees in the center of the picture on the ridge.	Tanoak trunk with weeping wounds typical of this fungal infection.
Tanoak sprout with an early infection. The bark has been stripped back to show the discolored vascular system.	The symptom produced on this baylaurel, or myrtlewood, is just chlorotic leaf tips.
Poison Oak can also get this disease. Note the weepy areas on this branch.

Cultural control: Control efforts in Oregon are focused on eradicating the pathogen where it is found and preventing new infections beyond the current quarantine area.

Do not transport firewood or other plant materials (bark chips, sawdust, mulch, etc.) or soil from diseased areas in California or southwest Oregon. However, these items may be transported if they have been kiln dried, heat treated, or otherwise sterilized or bear an official “Disease Free” certification. Harvest of forest products (such as timber, greens and mushrooms) from the quarantine area is strictly regulated and generally prohibited.
Wash shoes, vehicles, bikes, etc. if you visit infested areas of California or southwest Oregon.
Contact the Oregon Department of Agriculture if you see or suspect trees or plants in Oregon with symptoms of this disease.
Remove and burn all leaves and branches of dead plants. Sterilize pruning tools after use with bleach or other suitable disinfectant.
In Oregon, the Nursery & Christmas Tree Program Supervisor at ODA must be notified if importing nursery stock from any source (out-of-state or international). Plants must be certified as free from P. ramorum and have a copy of the official certification shield.

References:
Goheen, E. M., Hansen, E., Kanaskie, A., Osterbauer, N., Parke, J., Pscheidt, J., and Chastagner, G. 2006. Sudden oak death and Phytophthora ramorum: a guide for forest managers, Christmas tree growers, and forest-tree nursery operators in Oregon and Washington. Oregon State University Extension Publication EM 8877. 16 pp. http://extension.oregonstate.edu/catalog/pdf/em/em8877.pdf

Rizzo, D.M., M. Garbelotto, J.M. Davidson, G.W. Slaughter, and S.T. Koike. 2002. Phytophthora ramorum as the cause of extensive mortality of Quercus spp. and Lithocarpus densiflorus in California. Plant Disease 86:205-214.

The California Oak Mortality Task Force http://www.suddenoakdeath.org

Content edited by: Jay W. Pscheidt on January 1, 2009

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