Olive tree tuberculosis or knot, is one of the diseases of the olive tree. Warts that appear in olive trees are caused by the infection of the bacteria Pseudomonas savastanoi (Janse, 1982) or pv. savastanoi.
The applications of certain treatments and olive care can help disease control. However, current products only help eliminate olive knot disease partially.
Curiosities: The bacterium that causes olive tree tuberculosis Pseudomonas savastanoi pv. Savastanoi is a subspecies that does not infect oleander. In contrast, the bacterium Pseudomonas savastanoi affects oleander and can also form warts or tumors in the olive tree.
Symptoms of Pseudomonas savastanoi
The bacteria that causes the olive tree root can affect any part of the olive tree (olives, leaves, branches, trunk, roots…).
The infection occurs through the wounds present in the olive tree. These injuries may be due to the activity of insects, incidence of hail, frost, pruning, damage during la collection, etc…
During the initial phase small bulges of greenish and smooth surface are formed.
As the development of the bacteria progresses, the bulges grow to a size normally of 2-3 cm. During this phase the warts crush and change color taking brown tones.
In the final phase the tumors crack and darken.
On some occasions, fruits with depressed, small and brown spots may appear.
Development of the olive grove
Olive tree tuberculosis causing bacteria are found mainly within of the tumors. The rain distributes the bacteria across the surface of the olive tree taking advantage of the wounds to enter and infect. Depending on the size or length of the wound, the tumors may be isolated or joined together forming chains.
Once the infection is provoked, the bacteria alter the hormonal levels of its area of influence. This induces the olive tree to a process of hyperplasia (disorganized cell multiplication) that ends up developing the tumors or warts of the olive tree’s rust.
The optimal conditions for the bacteria are temperature between 21 and 24 ºC together with conditions of very high humidity.
Infections that occur during fall-winter are not visible until spring. In contrast, spring infections can develop tumors only after two weeks.
Major infections cause a general weakening of the olive tree, severe defoliation and dry branches. As a consequence, the production of olives is reduced and the quality of the oil is worsened.
Olive knot disease treatment and control
Thanks to the knowledge of Pseudomonas savastanoi, it is possible to apply cultural measures that prevent its spread. Also the application of certain treatments is useful for the chemical control of the disease.
Eliminate branches with presence of pseudomonas savastanoi. Tumors are the main point of spread of the bacteria that cause the disease.
As we well know, rain and wounds are two risk factors in the development of olive tree tuberculosis.
Therefore, avoid at all costs the collection of olives in wet olive trees or with an imminent probability of precipitation.
Mechanized collection using combs causes multiple injuries to the branches. At present, the widespread use of these vareadores is favoring Pseudomonas savastanoi infection.
In olive groves of sensitive varieties such as Cornicabra it is not advisable to collect with this type of machinery.
Plant resistant olive varieties to the rust.
Take advantage of dry weather to prune and disinfect pruning tools.
The ecological treatments with copper used against the olive peacock spot, help in the preventive control of olive knot disease. These treatments reduce bacterial populations, limiting their capacity for infection.
It will be necessary to perform additional cupric treatments when wounds are caused by frost or hail.
Olive resistance to olive knot
We will establish three levels of resistance to Pseudomonas savastanoi: resistant, moderately resistant and sensitive.
Knot disease resistant olive trees
We consider olive trees resistant to olive varieties that have few infections of the disease.
Alfafara, Leccino, Dolce Agogia, Callosina, Ascolana Tenera.
Moderately resistant olive varieties
They are those olive varieties that show intermediate behavior between resistant and sensitive.
Pico Limón, Cipressino, Hojiblanca, Picual, Peranzana, Negra de Sabiñan, Chamomile Cacereña, Picholine Marocaine, Lechin de Granada.
Olive tree tuberculosis sensitive olive plants
These varieties have a high susceptibility to be infected by the bacteria that cause rust.
Arbequina, Arroniz, Cornicabra, Morisca, Frantoio, Picudo, Blanqueta, Arbosana, Koroneiki, Taggiasca, Cerasuola, Rosciola, Pendolino, Preserves from Elvas, Biancolilla, Moraiolo, Manzanilla Sevillana, Ocal, Castellana, Gordal Sevillana, Verdial de Badajoz, Birdhouse.
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