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There are always new things to see in the field. Some things show up on occasion, but reliably, like citrus leafminer starts damaging new leaves in the fall. You start to see the leaf spots from Persea mite in the fall, even though they started their nesting/feeding activities in the late spring. Then some things show up irregularly. There's a fungus that hits citrus and other plant species – oleander, bottlebrush, holly, Natal plum, Brazilian pepper, eucalyptus – but mostly landscape species.
Sphaeropsis tumefaciens pops up here and there, this year and then not for several years. I've only seen it in Ojai, but Craig Kallsen in Kern Co. says that it's not uncommon in Bakersfield backyard citrus. It creates knobby growths, galls or tumors along branches. I've seen it on mandarin (‘Pixie'), lemon, Valencia and ‘Late Navel'. Whenever I see it, I immediately think of glyphosate damage.
A lot of times, you can see twisted leaf growth coming out of the galls. Classic herbicide phytotoxicity symptoms. But symptoms are just that, they don't tell you what caused that symptom to happen. In the several cases I've, seen only one out five has been an orchard that used herbicides. So it wasn't a reaction to glyphosate that caused the unusual growths.
These woody growths take several years to form. They don't show up just after an herbicide spray. It probably take a few years for them to show up. It's not until someone is pruning that they probably notice the galls.
In fact, it might be the pruning that is spreading the spores that causes the infection. Moisture helps spread the fungus. Another reason not to prune citrus during the rainy season.
While looking through the literature, I came across a reference to galls forming in avocado caused by Sphaeropsis – this in Mexico, http://www.avocadosource.com/WAC2/WAC2_p129.pdf. I have seen symptoms like that here
Also causing a whole fruit to form a gall. Truly a bizarre sight
But of course, this is my speculation, since these symptoms have not been tested foe their cause, as far as I know.
What causes the symptoms in Mexico might be different in California.
How to treat these galls in citrus? Cut them out if you can, but in many cases they are right in the middle of a structural branch. It is desirable to get it out of the orchard to prevent its spread. With the limited experience we have with this disease, it doesn't seem to impair yield at the levels of infection i have seen.
