There Cercosporiosis of the olive tree (or plumbing of the olive tree) is a serious fungal disease that affects olive groves. It is a disease known since the end of the nineteenth century and which has always affected the different areas where these trees are present in leopard spots. In recent years there has been a greater presence of cercosporiosis, with new areas affected by the disease and a worrying increase in damage.
In this article we understand the biology of the fungus, the damage it causes and how to carry out the biological defense.
The damage caused by cercosporiosis
Cercosporiosis of the olive tree is caused by the fungus Pseudocercospora cladosporioides.
It is a disease that mainly affects women olive leavesalthough with increasing pressure of the pathogen more and more damage to the drupes is recorded.
On the foliar apparatus we have several symptoms, different between the lower and the upper page.
- On the lower page you can see irregular spots, from where a thin layer of conidiophores caused by the pathogen comes out. The color becomes gray, hence the vulgar name for plumbing of the olive tree.
- On the upper page, in correspondence with the underlying spots, you will see first yellow spots (chlorosis) and then necrotic. As the disease progresses, in the spring period, the leaves fall off completely.
- On the young branches there may be the presence of irregularly shaped, grayish spots.
- Small lesions, up to 1 cm in diameter, can be seen on the fruit affected by cercosporiosis of the olive tree. These lesions appear as depressed or sunken areas, brown in color, with a yellowish halo. Depending on the cultivar, the lesions on the fruit have a variable intensity.
The damage to the olive production
If the degree ofinfestation of olive plumbing is high, the foliage of the trees can undergo strong defoliation. The loss of the leaves inevitably compromises the production, causing serious losses to the olive grower.
When the attack of the pathogen is on the fruits, there is an early drop, which generally occurs before the olive harvest. These, therefore, fall without giving the olive grower the opportunity to intervene.
In table olives the damage is serious because, even if they do not fall, they are no longer appreciable on a commercial level.
In olive oil olives that can be harvested, on the other hand, the cercosporiosis determines a higher level of oxidation of the oil, without however affecting the degree of total acidity.
How the pathogen of olive plumbing works
The pathogen of cercosporiosis, P. cladosporioides, develops on the leaves. Once developed, it can penetrate the cuticle through small lesions or through natural openings (stomata).
Following the penetration, the symptoms we have described above occur.
The fungus produces conidia that allow it to spread. It also produces sclerotia, that is, conservative structures that allow the pathogen to survive in unfavorable conditions.
Climatic conditions favorable to the spread of Cercosporiosi dell’olivo
The best climatic situations for the formation and diffusion of conidia are those with temperatures between 12 and 28 ° C and high air humidity. So typically in the spring and fall.
Harsh winters and hot and dry summers naturally limit the spread of cercosporiosis.
The spread in spring and autumn is carried by wind and precipitation, which carry the reproductive organs of the fungus from one plant to another.
As the infestation progresses on the crown of the tree, a loss of precious cellular material from the leaf tissue is determined, hence the appearance of the spots on the lower page and of chlorosis on the upper one.
How to prevent olive cercosporiosis
A correct cultivation of the olive tree is the basis of the agronomic prevention from cercosporiosis. The plumbing of the olive tree, in fact, can be limited using the following techniques:
Which varieties of olive trees resist the Cercosporiosis of the olive tree?
There are varieties of olive trees that have proven to be more resistant to cercosporiosis, others that are more susceptible.
This information is important, especially when we plant a new olive grove in areas where the disease is known to be present.
The most resistant varieties are:
- Tonda Iblea,
- Nocellara Etnea,
- Leccino (also resistant to xylella fastidiosa).
The more susceptible ones are:
- Crusher
- Moraiolo
- Nocellara from Puglia
- Rosciola
- Ogliarola
- Moorish
How to defend the olive trees from plumbing
The plumbing of the olive tree has symptoms and temporal analogies with another and better known disease of the olive groves, namely the peacock’s eye (or cycloconio).
For this reason it has always been considered that the treatments of the latter disease are also sufficient for cercosporiosis.
The copper salts
Under the biological regime, the prevention of the olive cercosporiosis it is carried out essentially with copper salts, in particular oxychlorides. It is about products allowed in organic farmingwithin certain limits of use.
Specifically i treatments with copper they are carried out in the autumn period, immediately after harvesting; or in early spring, immediately after the pruning operations.
These two treatments can go up to four in the case of severe infestations.
In summer it is not advisable to carry out treatments, as there is a risk that they cause burns and give rise to phytotoxicity phenomena.
Kaolin
A certain effectiveness against the plumbing of the olive tree is obtained by carrying out the summer treatment with kaolin. This is mainly used in the fight against oil flybut its action is also useful against fungal diseases.
For the application of kaolin the exact opposite of copper salts applies, as it protects against insolation; it is non-toxic and washes easily.
As we have seen, in pre-harvest the danger of the olive tree seeker is high. The use of kaolin therefore comes precisely at one of the moments of greatest risk of infection.
Here you find specific kaolin packages for organic farming.
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