When trying to determine if an oak may have SOD (caused by the plant pathogen Phytophthora ramorum), the first step is to determine if the tree lies within 1 km of a known outbreak. This can be done by accessing SODMAP at www.sodmap.org or by uploading the free “SODMAP Mobile” app to your smartphone. Stand next to the tree in question and tap the risk button. A response of moderate or high risk would suggest Phytophthora ramorum may be present. The next step is to confirm it is indeed P. ramorum. Make sure the oozing is not wetwood, or bacterial flux, which typically is associated with much more oozing and often has an unpleasant odor. Bacterial flux usually has a watery secretion running down the trunk that originates from a wound or branch crotch. If all symptoms align with SOD, the next step is to test for P. ramorum. If a symptomatic California bay laurel tree is within 10 m of the oak, collect symptomatic bay leaves for testing. This is not a definite diagnosis for the oak, but it may be an acceptable one that does not involve wounding the oak tree for sampling. Bay-based diagnosis for an oak may be less accurate after multiple years of drought, as bays may actually turn from SOD positive to SOD negative during extended dry conditions. One can get bay leaves tested by participating in one of the annual SOD blitzes (www.sodblitz.org) or by submitting samples to the California Department of Food and Agriculture. Testing the oak requires debarking a portion of the tree until the margins of the putative SOD lesion under the bark are visible and then plating the margins of the lesion on Phytophthora-selective medium for laboratory analysis.
I have an oak in the Bay Area that is oozing liquid from the trunk base. Should I test it for SOD? If so, how?