This is the main fungal disease in olive groves. The annual costs for controlling it are quite high, at least in areas of medium to high relative humidity.
The repilo disease is a fungus that develops on the upper side of the olive leaf, feeding off its living tissues. Infected leaves are dropped by the tree, causing serious defoliation that directly affects both the photosynthetic capacity and the exportation of minerals and photoassymilates, which negatively affects production.
Therefore, repilo infections will occur in microclimate conditions with high ambient humidity and mild temperatures. These conditions occur mostly in spring and fall, in valleys with abundant fog, wetlands with high relative humidity.
Although it might seem contradictory, rain is not what causes the infections; rain drops can drag away the spores before they culminate in infection.
There are passive means of control, for example, pruning, that reduces density and thickness of the crown, thus promoting greater ventilation and reducing the relative humidity in the leaves.
The classic method of prevention is treatment formulated with copper.
Copper treatments are usually applied when the climatic conditions start to become favorable for the infections. Each farm is different, but in general it is typically around the start of fall in October, and at the beginning of spring in the month of April.
During summer, there is little ambient humidity and high temperatures, so it is impossible for the spores to infect the leaves. During winter, while there may be a certain favorable relative humidity, the low temperatures slow the spore metabolism way down and it cannot finalize the infection.
In areas where repilo is not often present, fungicidal treatments can be reduced to one or zero times per year, while in areas more prone to repilo it may be necessary to apply treatments 2 or more treatments over the year, for example, at the beginning of the year and /or at the beginning summer.
Nowadays translaminar systemic fungicides are combined with the classic preventive copper to complete the erradicating effect that copper fungicides lack.
For the application of foliar fertilizers on the olive tree, they are often applied at the same time as the fungicide.