Disease severity may quickly reach epidemic proportions in oil olives because the late-season harvest, typically mechanical, proceeds after the onset of fall rains when fruit are physiologically mature and oil content has increased.
Figure 1. Disease Cycle of Olive Knot. Illustration by Heather Hartzog
Galls are generally produced at wounds and natural openings (ie. leaf scars, pruning wounds, hail/frost damage) where the bacterium gains passive entry after dissemination during rain events. Consequently, conditions promoting disease severity include: rainfall, mechanized cultural practices (particularly when rain is likely), and freeze damage.
In seasons where olive harvest proceeds into the rainy season, the probability of heightened disease severity relates both to the availability of fresh infection courts (peduncle scars), as well as a delay in post-harvest copper application.