I have an oak tree (Quercus kelloggii) on a vineyard property that recently keeled over after that last strong storm.
I see on the Garbelotto web site that oaks have to be tested by bark, not leaves, and that there is some special skill involved so I need to contact someone who knows what they’re doing. Is that something you can help me with?
I received that email a few days before the Sudden Oak Death Blitz was to be held here in Napa on May 6. The “Garbelotto lab” runs it: UC Berkeley Forest Pathology and Mycology Lab.
I looked at the photographs attached to the email and saw the remaining, fallen trunk of a huge black oak. It is one of the oak species known to be susceptible.
Here is my response:
From the photo it is clear your black oak had extreme decay in the trunk.
It is out in the open, apparently well away from plants and trees, especially California bay laurels that spread the disease.
I feel there is little point in pursuing testing even though that area probably has pockets of infected bay laurels.
Have you noticed standing dead coast live oaks nearby? The ones in the background of your photo look OK.
Isolating Phytophthora ramorum (the organism that causes SOD) from an infected oak is a tricky and technical.
Early on, the California State Lab in Sacramento would send out testing kits only for trained collectors.
They have not offered that service for many years, as far as I know.
The sampling method is something like this:
The lab sends you a kit containing a “PARP” plate, a Petri dish with Agar jelly that feeds the disease organism.
You excise bark until you find the irregular dark line in the cambial zone marking the location of the active disease organism.
Various organisms can cause such a margin.
You shave out a section containing the dark margin, use a flame to sterilize tweezers, let them cool, and get a small piece of the margin.
You place the sample on the PARP Plate, put on the cover, label it, put it with a cool pack in the shipping package and send it on overnight shipping to the lab.
I got one positive, one time many years ago.
I doubt the Berkeley Lab would do sampling of a fallen dead tree out in an open area, far from bay laurels.
The lab’s current technology employs multiple steps to isolate the disease.
Here is some information from the lab’s website:
— Agar jelly plate. (described above)
— Immunoassay: The EIA method uses antibodies to identify the presence of proteins or carbohydrates unique to Phytophthora. The EIA method can serve as a low-cost alternate pre-screen before PCR analysis.
— PCR Analysis: The polymerase chain reaction method. The plant material is extensively processed to extract, isolate, and purify the target DNA unique to P. ramorum.
— There is a “Do -it-yourself’ test, like a pregnancy test, made by Agdia. It uses bay laurel leaf samples, not the oak itself. Here is a link to the manufacturers information page.
The do-it-yourself test is best used as a pre-screening test for the presence of Phytophthora but not definitive for P. ramorum. There are various species of Phytophthora that infect oaks but only one causes SOD.
For your own use, I recommend you attend the SOD Blitz and get the smart phone app: SOD Map Mobile.
It is a free download that includes a Risk button that tells you where the disease has been found in relation to where you are standing at the time.
The Risk is based on sampling of California bay laurels, done by volunteers in the annual SOD Blitzes.
The point is: First assess the risk. Be familiar with the foliar symptoms in California bay laurel trees, the main carrier of the disease. Learn the management guidelines and then take appropriate action.
The May 6 SOD Blitz results will be published in October.
Our next Napa SOD event is a training session for the general public. It is scheduled for Oct. 28 at 10:30 a.m.at the Napa County Library.
It is free, open to the public, and there is no pre-registration.
Put it on your calendar.