While the improvement in rainfall last winter and this spring brought us some relief from drought it also brings an increased risk of Sudden Oak Death disease spreading from infected California bay laurel trees into susceptible oaks.

In a recent announcement, Matteo Garbelotto, director of the UC Berkeley Forest Pathology and Mycology Laboratory said “The rainfall levels officially make 2016 a year in which Sudden Oak Death (SOD) may spread dramatically. This comes after four years of very limited spread of the disease, due to drought conditions. Despite the drought, we did observe some new outbreaks in 2015, suggesting that in 2016 we will witness many more. SOD is present on more than 500 miles of coastal forests, hence the help of volunteers to survey such a large region is absolutely necessary.”

Volunteers at 20 locations from Mendocino to San Luis Obispo are working again this spring to locate and map the disease. This is the 10th year of the ongoing effort and the sixth year in which Napa will participate. The Napa Blitz on June 4 is the final one this year in the statewide effort.

Results of the surveys have shown the disease has its ups and downs. “Downs” correlate with drier years and “Ups” with rainy years. But a new study (reported in this newspaper on May 6: “Tree Disease Might Be Unstoppable) by the National Academy of Sciences claims that we missed the opportunity, back around 2002 to eradicate the disease early on when “statewide elimination may have been possible.”

The genie is out of the lamp. Now we need to manage it the best we can, and we have 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.

In areas that are conducive to infection, like wetter portions of northwestern California, we may not be able save the oak woodlands in their current form but we can save some of the trees.

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 a one-hour training session by the UC lab director or research PhD, 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 a big help 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.

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Samples are returned 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. November is considered the best month to apply a special systemic fungicide to oak trees selected for protection.

Once the degree of disease risk is determined, property owners can make informed decisions for prevention and management.

There is only one preventative chemical treatment registered in California, produced by two different companies: Agri-Fos (Monterey; AGRICHEM MANUFACTURING INDUSTRIES) and Reliant (Quest Products Corp.) Both contain the same 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 active ingredient soak into the vascular tissue.

Dr. Garbelotto says, “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.”

The Napa SOD Blitz is on June 4, 10 a.m., at the Napa Resource Conservation District conference room 1303 Jefferson St., Suite 500B. There is no pre-registration. Just show up and take the opportunity to learn and make a positive contribution by giving a little of your time.

Bill Pramuk is a registered consulting arborist. Visit his website, www.billpramuk.com, email questions to info@billpramuk.com or call him at 707-226-2884.