What is Sudden Oak Death?
You might have heard the term “sudden oak death” before. Especially if you have oaks on your property. But what does it mean? What causes it? Thanks to our expert team at Trusty Tree Services, we’ve put together this beginner’s guide to what sudden oak death is, what causes it, and how to properly diagnose and manage it.
As a general introduction, sudden oak death is a disease that affects trees. It’s caused by a fungus-like plant that’s known by its Latin name, Phytophthora ramorum. It was first widely recognized as a tree disease in the middle of the 1990s. The disease primarily affects several specific species of oak, including coast live oak (Quercus agrifolia) and an oak relative, tanoak trees (Notholithocarpus densiflorus).
However, the fungus that causes sudden oak death doesn’t just limit itself to infecting oak trees. It can also infect other plants, including rhododendrons, camellias, and other common horticultural plants. The result is known by the name of ramorum blight. Keep on reading to learn more from the Edmonton arborists on our team at Trusty Tree Services.
A Brief History and Background of Sudden Oak Death
Sudden oak death has been recognized since the mid-1990s. It’s killed millions of tanoak and oak tree species. The susceptible plants include coast live oak, California black oak, Shreve oak, and canyon live oak. However, it’s also been linked to twig and foliar diseases in a multitude of other plant species, including Douglas fir and coast redwoods.
In North America, the first infestation of P. ramorum was discovered and identified in 2001, in a rhododendron nursery in Santa Cruz County in the United States. However, the North American nursery industry didn’t feel the full impact of the pathogen until 2004, when several large West Coast nurseries inadvertently shipped infected plants across the United States.
Despite being recognized in the mid-1990s, the origins of sudden oak death aren’t currently known.
The P. Ramorum Pathogen
Phytophthora species are well-known plant pathogens. They’re water molds that do exceptionally well in moist, humid conditions. Although the majority of hosts don’t die from the disease caused by the pathogen, they do play a key role in spreading P. ramorum. That is, they’re used as breeding grounds for what’s known as inoculum (which is the source material that’s used to start a new host of the pathogen). That inoculum is spread through a variety of ways, including water or human activity.
However, oak species affected by P. ramorum are terminal hosts. That means that the pathogen doesn’t spread from their intact trunks. They’re usually infected by exposure to spores that are produced on the leaves of other infected plants nearby that harbor P. ramorum.
Properly Diagnosing P. Ramorum
When it comes to detecting P. ramorum, it can be difficult. That’s because the symptoms caused by the P. ramorum pathogen are very similar to those that are caused by other fungi, insects, or even the environment. There’s only one way to properly detect P. ramorum: taking a sample and performing an analysis for detection of the pathogen.
If you’re worried about the possibility of sudden oak death, then you need to consult one of the two published guides on detecting P. ramorum. These are the Wildland Diagnostic Guide and Nursery Diagnostic Guide, which will help you decide whether it’s worthwhile to send in a sample for laboratory analysis for detection.
Symptoms of P. Ramorum
There are two types of symptoms caused by P. ramorum. These depend on the foliar host. Trunk or branch cankers often form on tanoak trees and certain species of oak. However, most shrubs and plants will show leaf spots that are often seen in combination with branch dieback. However, for oak species, trunk and branch cankers are the most damaging, often resulting in death.
Once the trees have been weakened by Phytophthora ramorum, the infected trees are then often targeted by bark beetles and that hastens their death. Once parts of the tree have died off, fungi that’s been dormant within the tree might then begin to grow, which can include Annulohypoxylon thourasianum.
Now, foliar leaf spot and branch symptoms are usually only lethal when plants are young. But even those infected or susceptible plants play a role in spreading the pathogen. That’s because these plants are used by the pathogen as it reproduces and will sporulate on many of these species as a source of inoculum.
Symptoms of P. Ramorum in Oak Trees
For oak trees, the P. ramorum pathogen gained the name “sudden oak death” because of how quickly trees infected with it decline. Leaves rapidly darken throughout the canopy, and there’s no period of prolonged decline. Rather, it takes between two and four weeks for the tree to die following the presentation of visible symptoms.
However, thanks to intense study, death of the tree itself due to P. Ramorum is typically caused by a long period of infection, which can be more than two years. During that period of incubation, the only external symptoms that might present include insignificant oozing that’s difficult for most to detect.
The danger isn’t just caused by Phytophthora ramorum, either. The infection of sudden oak death is typically accompanied by other infections, such as ambrosia beetles (i.e., M. Dentiger), bark beetles, and the fungus Annulohypoxylon thouarsianum, which is a decay fungus. Now, these might be secondary to the P. ramorum infection, but they do further weaken the affected tree, which can hasten its death.
Need Help Diagnosing and Managing Sudden Oak Death? Contact Trusty Tree Services Today
Although there’s no known cure for P. ramorum infections, you can take preventative measures to lessen the ecological impact of the pathogen. If you’re looking for help managing P. ramorum or other diseases that affect your trees, you need to make the call to Trusty Tree Services today! We can help with everything from tree assessments and diagnosis to tree removal.
If you’re noticing suspicious leaf spots or other signs of P. ramorum, then it’s time to call Trusty Trees for comprehensive tree services here in Edmonton. Give us a call at 780-860-5500 or contact us online today to get started!