Earlier this spring, oil olives with severe defoliation in San Joaquin county were sent in for diagnosis by UC Plant Pathologist Florent Trouillas. He has isolated a putative pathogen, Neofabraea species. In addition to defoliation, leaf lesions and elongate twig lesions were also associated with this fungus (see photos).

Defoliation associated with the new olive disease on Arbosana olives. Photo credit: F. Trouillas.

Leaf spotting associated with Neofabraea on Arbosana olives. Photo credit: F. Trouillas.

Elongate twig lesions associated with Neofabraea on Arbosana olives. Photo credit: F. Trouillas.

Here is what we know so far about this disease:

• Symptoms include defoliation, leaf lesions, twig lesions, and fruit spotting (but maybe not all of these together).
• So far, the pathogen has been detected from Arbequina, Arbosana, Coratina, Picholine, and Frantoio.
• This, or a closely related pathogen, has also been associated with olive diseases in Italy, Spain and Portugal.
• In California, the disease has been positively confirmed in Sonoma, Glenn, and San Joaquin counties.

Unfortunately, the list of what we don’t know is significant:

• The species of pathogen(s) involved in the disease.
• Anything about the biology or epidemiology in California.
• Methods for controlling the disease.
• What conditions this growing season caused symptoms to be so prevalent.

If you see some of these symptoms in your orchard, please contact your local farm advisor to sample and confirm presence of this disease.