Anthracnose (Colletotrichum sp) is a olive disease of increasing importance in the Spanish olive grove.
It is produced by fungi Colletotrichum acutatum and Colletotrichum gloeosporioides.
Initially it only affected olives, but currently fungi produce a toxin that weakens the olive trees by drying the affected branches.
It is in the rainy autumn when the fungus has a greater development and produces significant damage, especially in the olive varieties more sensitive to the disease.
The olive anthracnose occurs in the branches with a significant amount of infected fruits and produces the dry of branches up to 5 centimeters in diameter.
It is easy to distinguish Colletotrichum of Verticillium. The anthracnose produces a total defoliation of the affected areas (the green leaves come off very easily). However, the Verticillium keeps the branch with dry leaves that are rolled up for a long time.
Distribution: The fungi that cause “Colletotrichum sp in olives” are distributed throughout the world. Only in very cold or desert areas they have not been able to be colonized.
Symptoms of Anthracnose olive infection
In the First stage of development, symptoms are only detected in olives. The first symptoms are round and necrotic spots with brown color, ocher or brown. Initially the fruits have one or more round and growing spots. In the final phase, these spots grow and come together, completely infecting the olive.
When the humidity is high, on the spots s it forms a jelly-like and orange substance with a lot of spores . The fungus receives the common name of Colletotrichum sp in olives due to this reason.
As the infestation progresses, the olives fall to the ground or remain dry and mummified in the tree.
Olives infected by the fungus emit a toxin that produces an effect similar to that of leaf chlorosis. These chlorotic spots expand covering almost the entire leaf. Finally, the leaves dry and fall to the ground, causing significant defoliation.
Growths up to 3 years and 5 centimeters in diameter can also be affected.
Colletotrichum cycles
Colletotrichum sp has a very fast cycle (in favorable conditions one week)
1st Generation: The spores of the fungus remain dormant in the mummified olives of the previous year. The rains of autumn disperse the spores or conidia of the fungus that require the presence of water on the olives to germinate.
Although the fungus can also attack healthy fruits, it expands more quickly in olives with wounds. Being the especially virulent Anthracnose of olive tree with the olives that have been affected by the olive fly.
Secondary generations: the fungus manages to reach maturity just a week after infection, producing new spores with the capacity to contaminate more olives.
Anthracnose develops well with conditions of temperature of 10-30 ° C and high relative humidity, more than 93%.
Under these conditions the fungus can perform a large number of infection cycles, causing serious productive damage if appropriate measures are not taken.
Damages caused by the anthracnose of the olive tree
1.- Harvest loss: In many places, olives that fall to the ground cannot be harvested due to lack of profitability.
2.- Oil devaluation: Increase the degree of acidity, the oil color takes an unpleasant orange hue and loses much of its organoleptic characteristics. This also means a loss of value of olive oil.
3.- Olive tree weakening: An important anthracnose attack leaves the olive trees very weak for several campaigns.
4.- Wilt of inflorescences: the fungus can also affect the flowers of the olive tree producing wilting.
Treatments against Colletotrichum sp
There are several cultural practices that allow disease control. However, in humid areas with varieties that are not very resistant to the Colletotrichum sp, the treatment is essential.
Control / support methods or techniques against olive anthracnose
1.- Clarification: a good ventilation of the trees, reduces the humidity on the branches and limits the time of action of the fungi. This technique is also useful in the control of the black scale olive tree.
2.- Early harvest: pick up the olive before the disease reaches a worrying level of development, will allow us to keep the olive groves healthy.
3.- Olive fly control: The olive fly makes wounds in the olive that facilitate the entry and development of the fungus. Therefore, effective control of the olive fly is essential against the disease.
Phytosanitary treatments against anthracnose olives
If our olives varieties are sensitive to anthracnose and we are in a risk zone (high humidity during the fall). We are”obliged”to perform preventive phytosanitary treatments against the disease.
These treatments are compatible with those performed usually against olive peacock (cupric compounds) during spring and autumn. Voliam Targo and Syllit Flow are the commercial names of the authorized phytosanitary products today (2017).
Anthracnose resistance of olive varieties
The incidence of Anthracnose in the olive tree is affected by several factors. Typically, varieties of olives that are more prone to fly attacks are more susceptible to anthracnose.
They have good resistance to olive anthracnose: Picual, Manzanilla Cacereña olive tree
Neutral behavior against the fungus: Arbequina
They are sensitive to anthracnose of olive tree: Verdial from Badajoz, Manzanilla Sevillana, Hojiblanca, Picudo, Nevadillo Blanco de Lucena, Gordal Sevillana
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We have translated the information on our website from Spanish to English. Note that some words may have seen their meaning altered during their translation.