The good news in last year’s Sudden Oak Death Blitz was a very low rate of infection in the 116 samples collected by the volunteers in Napa. The bad news was higher rates of infection in other counties.
To date, the disease has killed more than 5 million oaks and tanoaks in California since its discovery in the mid 1990s, says a press release from Matteo Garbelotto, director of the UC Berkeley Forest Pathology and Mycology Lab.
Heavy and lingering rainfall in spring 2017 created increased infection rates but that did not seem to be the case here in Napa County.
Why? It could be that conditions in much of Napa County are less favorable to the disease than they are just across the Napa-Sonoma County line and along coastal California.
The disease is caused by Phytophthora ramorum, a water-dependent fungus-like organism. It spreads primarily in rainwater dripping from infected bay laurel leaves onto coast live oaks and a few other susceptible tree species. Research has shown that the majority of infections occur when conditions are right: Mild to warm and rainy.
Garbelotto has said the drought curtailed the infection rate somewhat but increased rainfall in 2017 gave it more opportunities to spread. These April rains we have just had support increased infection rates.
Sudden Oak Death (SOD) is present in more than 500 miles of coastal forests; hence the help of volunteers to survey such a large region is absolutely necessary. The annual SOD Blitz gives volunteers the opportunity to help.
Volunteers at 23 locations from Mendocino to San Luis Obispo are working again this spring to locate and map the disease. This is the 11th year of the ongoing effort and the eighth year in which Napa will participate.
The disease apparently arrived in California from Europe in infected nursery stock and quickly escaped into oak woodlands. There is no way to eradicate it. The best we can do is to manage it.
Here are several ways to do that:
— Assess the risk of infection in a given location.
— Select high-priority oaks for protection.
— Employ disease prevention and management practices that are known to be effective.
A primary function of the SOD Blitz is to assess disease risk at a given location. It can be a pleasant half-day outing for Blitz volunteers, especially working in pairs.
After the required one-hour training session, volunteers receive a packet of small envelopes with forms for recording tree locations and a few other data points for each California bay laurel sampled. Then they head off to locations of their own choosing to collect samples of bay leaves showing the typical infection symptoms.
The free smartphone app, SOD Map Mobile is essential in disease risk assessment and in filling out the sample collection forms. When opened at the location where the user is standing, the app provides the disease risk based on previous surveys and the GPS coordinates that can be written on the collection form.
Volunteers return the samples to a local drop-off location within 24 hours, where they are picked up and taken to the UC Berkeley Lab for analysis. Results are released in October, just before the treatment season begins. Halloween to Christmas is the best time frame to apply the systemic fungicide to oak trees selected for protection.
Once property owners determine the degree of risk they can make informed decisions for prevention and management.
There is only one preventive chemical treatment registered in California, produced by two different companies: Agri-Fos (Monterey; AGRICHEM MANUFACTURING INDUSTRIES) and Reliant (Quest Products Corp.) Both contain phosphonate, the active ingredient.
The material can be injected directly into tree trunks or applied by the “basal bark” spray method when combined with Pentrabark (Quest Products. Corp.), a surfactant that helps the phosphonate and water solution soak into the vascular tissue.
Updated recommendations now include management of bay laurels, soil incorporation of granular gypsum at a particular rate and radius around the base of the tree. It has been shown to enhance effectiveness of the phosphonate.
“While a few hundred people participate in the SOD Blitzes, the data they generate is used by hundreds of thousands, making it one of the most useful and consequential citizen-science programs in the country,” Garbelotto said.
The Napa SOD Blitz is on May 19 at 10 a.m. at the Napa UCCE Classroom, 1710 Soscol Ave. There is no pre-registration or fee.
First, download SODMap Mobile to your smartphone, then just show up at the Blitz.
Take the opportunity to learn and make a positive contribution. A wealth of information on SOD is available at this link: