The olive peacock eye, or cycloconium, is perhaps the most widespread fungal disease in olive groves. It is present throughout Italy, and its severity varies depending on various environmental factors. For example, there are olive varieties that are more or less susceptible to the olive peacock eye, and there are also pedoclimatic conditions that are more favorable to the onset of the infection. The management of the olive grove is also crucial in preventing this disease, with particular attention to the planting distance and the correct and periodic pruning operations.
Let’s get to know this disease better, see how to prevent it with good agronomic practices, and how to combat it with biological treatments performed at the right times.
What is the olive peacock eye?
The olive peacock eye is a cryptogamic disease of the olive tree caused by the fungus Spilocea oleagina. This fungus is a mitosporic belonging to the order Hyphales, family Dematiaceae.
The typical symptoms mostly appear on the green parts of the tree (leaves and petioles, small branches, fruits, and their peduncles), but the most evident damage occurs on the leafy part. Here, the olive peacock eye penetrates beneath the cuticle, colonizing it. In the outermost layer of the leaf epidermis, the fungus can remain latent for long periods. Subsequently, with favorable weather conditions, it infects the affected organs by breaking through the epidermis and sporulating on the upper leaf surface, mainly through hydrophilic means, meaning through water.
The symptoms on the leaves are distinctive: abnormal gray, round spots surrounded by a brown band appear. Around this spot (which can reach a diameter of 10-12 mm), in the warmer months, yellow, red, or brown-greenish halos appear.
The alternation of growth and stasis periods of the spots gives them a characteristic concentric zoning. At this point, the spot and the surrounding halo resemble the eyes on a peacock’s tail, hence the common name.
Even herbaceous branches can be attacked by the olive peacock eye, with symptoms similar to those on the leaves.
Fruits, on the other hand, are rarely affected. In these cases, small black or brown spots appear on the drupes nearing maturity. The fungus also causes slight depression.
Peduncles are often infected by the fungus as well. The noticeable symptoms involve rather elongated brown spots.
Main damage caused by the olive peacock eye to cultivation
The damage caused by the olive peacock eye to an olive cultivation is particularly concentrated in the lower part of the tree canopy. Leaves affected by the fungus fall, affecting the vegetative and productive activity of the olive tree. Both the production of the year and the reproductive and vegetative activity in the following years can be seriously compromised. The absence of leaves hinders the induction of bud flowering, which typically occurs in winter. This can significantly reduce olive production. The tree as a whole shows strong vegetative decline, with widespread dry parts in the canopy.
Leaf infection can occur at various times of the year, with spring being the most common period.
In severe infections, up to 80% of normal production can be lost.
Damage to the fruit peduncles also causes significant harm. Small elongated spots with a diameter of about 2-4 mm form on them. This type of olive peacock eye blocks the passage of sap and, subsequently, causes the fruits to fall. Infection in this case occurs at the beginning of fruit formation or in the early stages of ripening.
Seasons most at risk of infection
The olive peacock eye is active at different times of the year. Since high temperatures in summer and cold winter weather halt the development of the fungus, spring and autumn are the seasons when the disease is most prevalent.
The conditions that favor the development of the pathogen occur when there are 24-48 continuous hours of rain. A temperature between 5 and 25 °C is also required, with the ideal inoculation temperature being 20 °C.
When these favorable climatic conditions occur, the fungus conidia actively penetrate under the leaf cuticle. They settle there and form colonies. At this point, new conidia are produced on the surface of the infected parts. These are spread by rain or wind and infect healthy parts or other trees.
Usually, it takes a couple of weeks for symptoms to appear after infection, but in some cases, it can take several months.
How to prevent the olive peacock eye
Preventing the olive peacock eye primarily involves adopting good agronomic practices, both at the time of planting and afterwards.
First and foremost, when establishing a new olive grove, it is essential to use wide planting distances. It has been observed that in dense plantings, shading phenomena lead to reduced aeration of vegetation. This, in turn, creates more favorable conditions for disease attack.
Recommended planting distances vary from 5×6 to 7×8 meters if the planting arrangement is rectangular. If the planting arrangement is square, distances range from 6×6 to 7×7 meters. The larger values are suitable for vigorous cultivars with an expansive canopy development and open training forms. It is also known that groves in lowland, more humid areas are at greater risk compared to hilly environments.
Proper and regular tree pruning is also crucial. This helps to aerate the canopy and maintain vegetative balance.
We recommend reading our article on olive pruning for further insights into these topics.
Olive tree cultivars most resistant to the olive peacock eye
An important decision when establishing a new olive grove is the choice of varieties that are more resistant to the olive peacock eye. Below are some varieties listed with their sensitivity levels to this fungus:
- Cellina di Nardò, low sensitivity
- Cima di Mola, low
- Cipressino, low
- Coratina, medium
- Nociara, low
- Ogliarola barese, medium
- Ogliarola garganica, medium
- Ogliarola salentina, low
- Peranzana, medium
- Rotondella, medium
- Cima di Melfi, medium
- Frantoio, medium
- Leccino, low
- Moraiolo, high
- Pendolino, low
- Carolea, high
- Maiatica, low
- Picholine, medium
Biological defense against the olive peacock eye using copper-based products
In both organic and conventional agriculture, the most common method to prevent the olive peacock eye is the use of copper compounds. In organic farming, the use of this product is subject to regulation CE 889/2008 (1/1/2009). These methods have already been observed in combating peach leaf curl.
Biological treatments are carried out at two distinct times:
- Fall, immediately after olive harvesting
- Late winter-early spring, after pruning
Among the various copper-based formulations available to organic farmers, we recommend oxychlorides (which you can find here).
This biological treatment is highly effective in preventing the olive peacock eye. The copper product serves a dual function: it protects non-infected leaves and exerts a defoliating action on vegetation already affected by the disease.
Of the two copper treatments, the late winter-early spring one is more important. Copper has a phytotoxic action on already infected leaves, causing them to fall. This allows new leaves to grow on vegetation without sources of fungal inoculum. Copper acts on diseased leaves by penetrating the leaf mesophyll, thanks to the fact that the cuticular layer is damaged or lesioned by the fungus itself.
It is unlikely that fallen leaves will be able to infect the plant again, thus the existing healthy leaves are protected.
Remember to perform treatments on dry days and in the absence of wind. It is advisable to use personal protective equipment, such as gloves and masks with appropriate filters (which you can find here).
Kaolin as an alternative defense method
Recent field trials have shown that, in addition to copper-based products, kaolin can also be used in preventing the olive peacock eye. For further insights, please refer to our article on the use of kaolin in organic olive farming.