Olive peacock spot, bird’s eye spot or olive leaf spot (Cycloconium oleaginum (Castagne 1845)) is probably the most serious disease that affects the olive grove. Although there are effective treatments and some olive varieties have certain resistance, its incidence has an important impact on the productivity of the olive tree.
In Italy the disease is known as Occhio di Pavone, which can be translated as”peacock eye“. It receives this name for the comparison between the bird’s eye spot produces on the leaf and the appearance of the peacock’s feathers.
There are two main fungi that cause peacock spot on olive trees, the most common (with scientific name, Cycloconium oleaginum it is also known as Spilocaega oleagina and Fusicladium oleagineum) and the leaden (Pseudocercospora cladosporioides).
In this publication we will describe the characteristics of olive leaf spot with the most common presence in the Spanish olive grove.
Olive leaf spot is one of the most important diseases or pests of the olive grove together with the olive fly and the Prays. The ecological treatments allow an effective control of peacock spot on olive trees.
What is the olive peacock spot? Microscopic Description
Olive peacock spot is a Hypomycete fungus that is multiplied by conidia (asexual and immobile spore) in a piriform shape (similar to that of a pear) and color Brown. The spore is formed at maturity by two dissimilar and unitabicated cells (joined together through a”septum”layer). Conidia are formed alone in conidiophores (microscopic spore-producing structure) globose and with collarettes.
Symptoms of the presence of Cycloconium oleaginum
The mushroom of olive leaf spot mainly attacks the leaves, although it can also be found in the fruit and peduncle.
Sheet: brown spots of varying size and quantity appear on the surface or beam of the sheet. The spots are due to the fungus spores and may have ring or full circle shape.
During the spring the spots on the leaves are usually accompanied by a yellow halo, unlikely in autumn-winter. As the spots age, they change color giving rise to green, brown or yellow rings, similar.
When the heat of spring stops the development of the fungus, silvery spots may appear during the summer. On the other hand, with mild temperatures, small and irregular brown spots with reduced presence of spores are produced. These small spots are similar to those that can be observed in resistant varieties.
In the underside of the leaf dark spots may appear on the central nerve.
Fruit: the presence of Cycloconium oleaginum directly on the olive is less common. In such a case, small brown-black spots of variable size and circular-asymmetric shape could be observed .
During the maturation, the area infected by the fungus remains green while the rest of the surface of the olive changes color.
Peduncle: When the peduncle is affected the olives fall to the ground and the harvest is especially reduced.
Detection of olive leaf spot infection
Although the infection by bird’s eye spot apparently does not show symptoms on the leaf, its detection is possible thanks to the soda method. The olive leaves are immersed in a 5% sodium hydroxide solution for 15-20 minutes. After this time it will be possible to detect the presence of spots on the leaves affected by latent or incubated olive leaf spot.
Phases of disease development
Bird’s eye spot spreads due to the presence of infected leaves in the tree, the leaves present in the ground seem to have no influence.
After the periods of rain and high humidity the fungus fructifies, forming viable spores that can remain in the conidiophores for months. Once the spores are expelled from the conidiophores, their germination capacity lasts less than a week.
There is spore availability in the conidiophores throughout the year, however, it is in spring and autumn when their presence is maximum.
The spores of the bird’s eye spot are dispersed mainly by the rain, because of this the lower parts of the tree are more affected. Its dispersal capacity is low, although some insects can help its diffusion (Ectopsocus briggsi).
The spores germinate when there is presence of water or the humidity is higher than 98%, the optimum temperature is 15ºC although they admit a range between 0 and 27ºC. For the infection to be effective, the humidity conditions must be maintained for at least 1 or 2 days.
After infection, the fungus feeds and develops under the protection of the subcuticular layer.
The incubation (period without symptoms) lasts from 4 to 15 weeks. To detect the infection during this period, the soda method will be applied.
Damages produced
The fungus causes major damage, especially during the rainy years. Especially affecting super high density olive groves (with reduced planting frames), poorly ventilated (insufficient pruning) and which are located in humid areas (near rivers, streams, swamps…).
Like other fungi, Cycloconium oleaginum proliferates better in the humid climate zones. Therefore, within the olive tree itself, the incidence is higher in the northern area and the lower branches of the olive tree. In addition, olive leaf spot seems to affect more plantations with excess nitrogen compared to others with good potassium nutrition.
The final result of the fungus infection is that falls to the ground a significant amount of olive leaves. Usually olive leaves turn yellowbefore falling.
This fall of olive leaves causes the weakening of the tree, reducing its productive capacity.
Control techniques and treatments against peacock spot treatment
We can reduce the incidence of olive peacock spot, by using cultural techniques and the application of treatments with phytosanitary products.
Cultural control measures
Facilitate aeration of trees. This is improved by expanding planting frames and performing proper pruning .
Select favorable locations for the new olive groves.
If this is not possible, plant resistant varieties to the disease.
Balanced nutrition: avoid the excesses of nitrogen and ensure that the olive tree has potassium available.
Olive tree peacock spot treatment
Olive tree peacock is one of the most harmful olive diseases. Because of this, professional farmers carry out control treatments with different phytosanitary products.
By general rule two two annual treatments are carried out against the olive leaf spot. During these treatments it is advisable to use to apply foliar fertilizers with the most deficient nutrients.
When is the olive tree bird’s eye spot treated?
Depending on the time, when dealing with peacock spot on olive trees, it will be better to use a fungicide or another.
First treatment: it is done at the end of summer, if there is a presence of visible olive leaf spot or the incubation exceeds 1%, this treatment must be done before it rains. In case of low level of infection or resistant varieties, it can be expected to rain.
The advantage of waiting for the rains is that the foliar application to the olive treeis better assimilated. Obviously this advantage is lost if the infection by olive tree peacock is not controlled in time.
The most common during this treatment is the use of cupric fungicides.
Second treatment: It is performed in January-February when temperatures rise and conditions are favorable for fungus proliferation. The use of copper-based products is the most common treatment.
Third treatment: when the spring is rainy, a third application of products may be required to protect the olive tree from Cycloconium oleaginum. This treatment is especially necessary in disease-sensitive olive varieties.
In some situations, the third treatment with curative products may be applied to replace the second preventive treatment. If the fungus has been able to infect an important number of olive leaves, the treatment with copper will produce a significant defoliation, and its application may be counterproductive.
Products for the treatment of Cycloconium oleaginum
If we want to prevent the olive leaves from turning yellow and many leaves fall to the ground, we need to apply fungicidal treatments. So we can fight the fungus and deal with the disease that causes the olive leaves to fall.
Within the range of existing products for the fight against olive tree, we can distinguish between curative and preventive treatments.
Curatives can be applied with good results after infection of the fungus (provided that this infection is in the early stages of incubation).
The preventive have to be applied before the fungus infects the olive leaves. If your application is carried out after infection, we will cause the infected olive leaves to fall.
This fall occurs due to the phytotoxicity that induces the fungus on the leaf and also weakens the olive tree.
Within the preventive products they are usually applied: Copper sulfate (popularly known as Bordeaux broth ), Copper oxychloride, Copper hydroxide, Captam, Copper oxychloride + Mancozeb, Cuprous oxide (known for copper red ).
Several treatments with copper salts are authorized to be used in organic farming.
As healing products we have the Tebuconazole.
The best fungicide against olive leaf spot will depend on the time of application, being usual to apply preventive treatments at the end of the summer and curative treatments during the spring.
Before performing the treatment, we must ensure that the product used is authorized by the ministry for that purpose.
Level of resistance to the peacock spot of olive varieties
We can scale the resistance to the ring in a simplified way on three levels: resistant, moderately resistant and sensitive.
Bird’s eye spot resistant olive trees
We consider resistant to those olive varieties that hardly show symptoms of the disease.
Picual, Arróniz, Koroneiki, Arbosana, Frantoio, Piricuddara, Fraga, Dolce Agogia, Cellina di Nardo, Maurino, Frangivento, Ascolana Tenera, Leccino.
Moderately resistant olive varieties
Those varieties that are still affected by olive leaf spot do not do so virulently.
Arbequina, Picudo, Pico Limón, Alfafara, Chamomile Cacereña, Castellana, Negral de Sabiñan, Picholine du Languedoc, Cobrançosa, Nocellara Messinese, Tonda Iblea, Peranzana, Itrana, Shikitita.
Sensitive olive plants
In these varieties, the olive tree hardly show resistance to fungal infection. Therefore, control treatments must be applied precisely to maintain healthy olive trees.
Cornicabra, Blanqueta, Verdial de Badajoz, Gordal Sevillana, Lechin de Granada, Empeltre, Hojiblanca, Morisca, Villalonga, Nocellera del Belize, Rosciola, Manzanilla Sevillana, Giarraffa, Carolea, Changlot Real, Coratina, Santa Caterina, Casaliva, Moraiolo, Royal de Calatayud, Pendolino, Oliva di Cerignola, Callosina, Ocal, Ergot of Monterrubio, Picholine Marocaine.
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