By Norma Kline, OSU Forestry Agent, Coos and Curry Counties
If you have read news articles about Sudden Oak Death (SOD) in southern Oregon’s Curry County you may be concerned that trees on your property are at risk for infection. Sudden Oak Death has killed hundreds of thousands of tanoak since it was first detected near Brookings in 2001. Why has Sudden Oak Death been so damaging to our native ecosystems? Sudden Oak Death is caused by an introduced (non-native) pathogen called Phytophthora ramorum. Phytophthora ramorum is an internationally quarantined pathogen first described in California in the mid-1990’s and remains a serious threat to forest and nursery industries. Oregon’s interagency Sudden Oak Death program actively surveys and treats infestations at the leading edge of the disease.
Phytophthora ramorum spreads easily in the rainy and windy climate in southern Oregon. The disease advances across the landscape as spores on the foliage of infested tanoak spread to healthy tanoak. Spores are sometimes blown for several miles in windy conditions. Infested tanoak die within 1-2 years and often seem to die “suddenly”. If you are located near known infested areas (Figure 1) keep a close eye on symptoms of the disease on tanoak trees and other host species. The potential for a Sudden Oak Death infestation on your property increases the closer in proximity you are to an infested area. Early detection and treatment of Sudden Oak Death are important tools to help slow the spread of this disease across the landscape. Even if you are located outside of Curry County and any known area of infestation, it’s still important to monitor your forest for unusual forest health issues.
Common symptoms to look out for on tanoak include a darkened petiole (leaf stem) (Figure 2), tip blight, and bleeding at the trunk. Look for leaf and shoot blight symptoms on rhododendron, evergreen huckleberry, madrone, Oregon myrtle and salal (Figure 3). Shoot dieback symptoms might be observed on Douglas-fir, grand fir, and coastal redwood. While there are many host species known to show symptoms of SOD, Tanoak is the primary host for Sudden Oak Death in Oregon. Oregon white oak (Quercus garryana) has not been found to be susceptible. California black oak (Quercus kelogii) and canyon live oak (Quercus chrysolepis) are host species that can develop cankers and die, at this time these two species have not been found to be infested with Phytophthora ramorum in Oregon.
How to Identify Tanoak
Tanoaks (Notholithocarpus densiflorus) are a cousin to our true oaks (true oaks are in the genus Quercus). Tanoaks are evergreen (not deciduous) and have acorns like a true oak, but their acorn caps have bristles (Figure 4). Tanoak leaves are thick and leathery with a fuzzy underside (Figure 5).
What do you do if you suspect symptoms?
- Review photos of symptoms in Sudden Oak Death, Prevention, Recognitions and Restoration (note: the maps in the publication do not include the Port Orford detection) https://catalog.extension.oregonstate.edu/em9216
- Document the location of the diseased plant and take a clear, close-up digital photo of the plant part showing symptoms.
- If you are located in Curry County outside of a known infested area (known infested areas are represented by black or red dots on Figure 1), contact the Oregon Department of Forestry’s Sudden Oak Death program for further instructions (Randy Wiese, 541-294-8425).
- If you are located outside of Curry County, contact the Oregon Department of Forestry, Forest Health Unit, 2600 State St, Bldg D, Salem OR 97310. 503-945-7200. https://www.oregon.gov/ODF/ForestBenefits/Pages/ForestHealth.aspx or the local Oregon State University Extension office: http://extension.oregonstate.edu/find-us
- For landowners planning a timber harvest in an area subject to quarantine, review the Forestry Operations within the Sudden Oak Death Quarantine in Curry County, A Guide for Landowners
https://www.oregon.gov/odf/documents/forestbenefits/sod-tanoak-guide.pdf Contact your Oregon Department of Forestry Sudden Oak Death forester if you have questions regarding harvesting as it relates to SOD.
View more about the quarantine here: https://secure.sos.state.or.us/oard/viewSingleRule.action?ruleVrsnRsn=158438
Landowners in Curry County have been volunteering as citizen scientists to help with the early detection of Sudden Oak Death. Landowners place buckets with bait leaves (healthy tanoak and rhododendron leaves) under apparently healthy tanoak trees at the leading edge of the infested areas (Figure 6). Bait leaves are mailed to the LeBoldus lab at OSU every 2 weeks for analysis. A similar project involves placing bait leaves in streams. Those that live in the generally infested area near Brookings can help with the search for disease resistant tanoak trees by looking out for surviving tanoak and recording locations using the Treesnap app. Contact Norma Kline at Norma.Kline@oregonstate.edu for more information.
