SOD Update from Dr. Woodward: Georgia Nursery Detections and Homeowner Guidance

From Dr. Jean Williams-Woodward, April 9, 2004

By now most may have heard Phytophthora ramorum (SOD) positively identified on plants within five Georgia nurseries: John Deere #173 College Park; Greenbrier Nurseries Evans; Green Thumb-West Augusta; Cofer's Home and Garden Athens; Craven Pottery Commerce. Infected plants, all camellias, originated from Monrovia Nurseries Azusa, California. Only imported plants tested positive. No Georgia-grown plants positive. Hundreds of samples processed through Extension Plant Pathology lab in Athens; more being evaluated. Additional nurseries likely identified as USDA confirms results. More homeowners will contact county agents with SOD questions.

SOD killed oaks in California/Oregon, potential to kill eastern oaks. Oak infection = "dead-end" for pathogen. Infects through bark, causes girdling cankers killing tree. "Bleeding cankers" ooze sap, darkly discolored. Many calls about oaks dying across Georgia. SOD not identified on Georgia oaks. Years of drought followed by wet 2003 → root decay most often cause of oak decline/mortality. Insect borers attacked weakened trees contributing to decline. Borers cause sap oozing/bleeding along trunk staining black.

Oak infection dead-end because fungus not known to produce spores on infected oaks. Disease doesn't spread from infected oaks. Rather, fungus infects shrub hosts (camellia, rhododendron, viburnum, rose, honeysuckle, more) often found with oaks. Hosts not killed but leaf spots/blighting resemble leaf scorch. Fungus produces abundant spores on infected leaves, water-splashed to adjacent plants. Research recovered P. ramorum from soil beneath infected plants, and on hikers' boots, bike tires, clothing. Unlike other Phytophthora, doesn't infect roots—only aboveground parts.

Links to websites with SOD info, pictures of infected plants. Look to familiarize with symptoms, especially on camellia: tan to brown, zoned, water-soaked leaf spots starting at tip progressing to petiole; excessive leaf drop. GA Dept of Agriculture (GDA) Q&A on SOD in Georgia available. Feel free to use in articles/radio.

When asked if homeowner should dig up potentially SOD-infected plant: NOT recommending digging up and removing. Removal could spread disease faster as infected plants may wind up in municipal waste, shredded for mulch. Better: homeowners who purchased Monrovia plants monitor them, contact county agents for suspect samples to Homeowner Plant Disease Clinic in Griffin. GDA info sheet has more. Monrovia plants "branded"—specially labeled pots with "Monrovia" written across side, larger colorful labels. Only concerned about plants purchased/planted within last year, conservatively two years. Plants established many years unlikely infected.