Key Features
- Leaf spots/blight on shrubs
- Wet, oozing spots on oak bark
- Wood discolored beneath spots
Symptoms
Sudden oak death, more correctly called Ramorum canker and blight, has two names that refer to the two different symptoms that result: On oak and tanoak (and viburnum), plants die, sometimes quite quickly. On most other understory shrubs, like azalea, rhododendron, camellia, lilac, pieris, and kalmia, the disease is foliar problem and twig blight. Unfortunately, when the pathogen attacks these plants, it is able to reproduce and create tremendous amounts of spores, allowing the disease to spread to oaks, tanoaks, and conifers, killing them. The symptoms of the pathogen can be readily confused with other Phytophthora pathogens, so laboratory diagnosis is essential. Submit samples for diagnosis if sudden oak death is the suspected cause of disease. Contact a plant disease diagnostic lab for information on submitting samples. Keep in mind that many common landscape problems resemble P. ramorum infections, including boring insects, Armillaria rot, and other Phytophthora root and crown rots.
Biology
On oak and tanoak (and viburnum), plants die, sometimes quite quickly and on oak and tanoak, the pathogen is not believed to spread. On most other understory shrubs, like azalea, rhododendron, camellia, lilac, pieris, and kalmia, the disease is foliar problem and twig blight. Unfortunately, when the pathogen attacks these plants, it is able to reproduce and create a tremendous level of spores, allowing the disease to spread to oaks, tanoaks and viburnum, killing them. To date, introductions outside of California, Oregon, and Washington state have been contained, and eradicated. The distribution and host range for this pathogen has yet to be determined.
Management Recommendations
Once oak trees are infected, there is no known way to cure them. Therefore, management practices are directed at preventing the introduction of the pathogen through infected nursery stock, chiefly infected azalea, rhododendron, viburnum, lilac and pieris. Inspect any new introduction of nursery plants, particularly for signs of Phytophthora--any Phytophthora. This is good practice-period. The best way to manage this disease is to make sure it doesn't ever make it to the landscape.
Effective Pesticides
Pesticides are neither available nor recommended for managing this disease.
Resources
- Report this pest
- For more information about invasives, visit https://ag.purdue.edu/reportinvasive/
- Sudden oak death
- Sudden oak death from UC Davis
- Not satisfied with ID? Contact the Purdue Plant and Pest Diagnostic Lab
- Sign Up for the Purdue Landscape Report
