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Pruning - Diseases and pests that affect the olive tree

Pruning is an important, even essential, operation in the cultivation of olive tree. The purpose of pruning is to shape the tree, to encourage fructification or to allow the resurrection of an olive tree that has been abandoned. During the first two years after planting, the olive tree should not be pruned, or very little, depending on the variety (light training pruning). After this period, annual or biennial pruning should be chosen.

Training size

The first pruning should be carried out when the tree has reached a height of about 1.50 m, to give it a balanced shape that makes it easier to work. Every year it is necessary to select the future pruners and to plan them at different levels, maintaining a reasonable height, because it's necessary to think about the annual treatments and about harvesting. The aim of formation pruning is to create a single trunk. This involves eliminating branches in order to strengthen the central trunk. In order to do this, the low branches have to be cut off so that a trunk of about 1 m in height is obtained. It is necessary to prune in such a way that the foliage is evenly distributed throughout the crown, so that it is well ventilated and receives as much light as possible. The olive tree does not produce new leaves every year, so it should not be deprived of more than 30% of its foliage.

Fruiting pruning

The purpose of this pruning is to select the twigs to be removed, which has the effect of aerating those that will ensure fruiting. This operation improves the lighting and promotes photosynthesis. In practice are to be removed:

- Dead, dry or diseased wood

- branches that have borne fruit and therefore will not produce any more.

- All twigs which are redundant: parallel or overlapping starts - The greedy ones which have generally grown the previous year but which do not bear fruit

Pruning should be carried out dynamically without dwelling on any particular point but, on the contrary, by turning around the tree and removing the selected twigs as you go along.

Pruning

A pruning, practiced every five or ten years, must be carried out to limit the growth in height of the tree. In general, it is not allowed to exceed 5 m in height.

Regrowth size

This is a severe pruning to be carried out when the tree is sick or too old. It is carried out on the branches or directly on the trunk. A tree can be rejuvenated in several ways: 
- by progressive rejuvenation, by cutting a limb every year or two.
 - by crowning, by pruning the trunk at the level of the lowest branches
 - by reception, by pruning the olive tree at ground level, then selecting one of the shoots that the tree will have sent out from the roots and removing the others. The following year, the root that produced the offspring is cut off to make the new individual autonomous.

Ornament size

The pruning is similar to the training pruning, it simply aims to give the tree a harmonious shape.
Diseases and pests of the olive tree:
- Plant parasites or fungi
- The fumagine or "black of the olive tree".
Occurs as a fungus spread by scale insects or the psylla. The twigs and the leaves of the foliage are gradually affected and become covered with black dust, preventing the tree from breathing. Preventive treatment in March with copper-based products or sulphates such as Bordeaux mixture.

Cycloconium or "peacock's eye".

This is the most damaging disease because it affects not only the leaves but also the fruit. It appears as brown or yellow circular spots. This disease occurs mainly in spring but sometimes in autumn. It can be controlled prophylactically by spraying with copper oxychloride or copper sulphate based products or by a fumagine-like treatment.

Verticillosis (Verticillum dahliae)

Verticillium is a microscopic fungus that lives in the soil and invades the tree when the sap rises. This happens when the roots are injured or after pruning. Symptoms include wilting of branches and twigs, and leaves curling up in a groove underneath. The disease is spread by infected tools. There is no treatment for this non-fatal disease of the olive tree.

Canker (or plum) 

This takes the form of wood growths that look like warts. They often appear after a frost or hailstorm. They are caused by a bacillus. Once an olive tree is affected, it is almost impossible to get rid of them. When pruning, try to remove the affected branches and always disinfect tools after use to avoid contaminating healthy trees. There is no treatment for this non-lethal disease of the olive tree.

Insect pests

The black olive scale

It is a hemipteran insect, oval, spherical, dark brown to black in shape and a few millimetres in diameter, which attaches itself to leaves in the larval stage and to twigs in the adult female stage. Its excrement, called honeydew, is an excellent support for the development of fumagin, also called olive black. The laying female dies and gives birth to larvae which, after three stages of development, give birth to a young female which quickly becomes a laying female.

The olive moth

The moth is a lepidoptera whose larva is a caterpillar 6 mm long and the adult is a silver-winged butterfly about 15 mm long. The moth attacks leaves, flowers and fruits in a cycle of 3 generations.
Phylophagous stage: in winter the caterpillar makes tunnels in the leaf.
Anthophagous stage: in spring the butterfly lays its eggs on the flower buds, which are attacked by the caterpillars, causing the flowers to abort and the berries to fall.
Carpophagous phase: in summer the butterfly lays its eggs on the olives, which give birth to the third generation of the year.

The olive fly

It is one of the most dangerous and damaging pests for the olive grove, its attacks cause a significant fall of the olives and a deterioration of the quality of the oil. The olive fly or Dacus Olea develops when the temperature becomes milder and lives exclusively at the expense of the olive. This pest causes very important damages. It lays its eggs in the olive contrary to the Moth which lays on the flower or on the olive. The preventive treatment to fight this parasite will be done in the month of July after petal fall by spraying an attractive mixture and insecticide, it is necessary to proceed by trapping to detect the appearance of the fly.

The Neiroun

The neirun or olive tree scolyte (small 2mm beetle) grows on trees weakened by frost and drought. It provokes along the branches and under the bark, holes and galleries surmounted by small balls of sawdust.

Hylesin

Hylesin (Hylesinus oleiperda) is a small bark beetle that attacks, contrary to neirun, vigorous trees, the affected parts take a purplish red color (to be eliminated and burned).

The Otiorrhynchus

This beetle of 7 to 8 mm feeds on leaves, the Preventive Treatment is done in May by spraying an insecticide. The Jasmine Moth It is a caterpillar that feeds on young leaves and causes the disappearance of the tips of young twigs. Attacks on adult trees do not pose a problem, however, on young trees, attacks can be damaging as they can compromise the growth of the tree and its future formation.

Thrips 

Family of mites, causes the deformation of leaves and twig ends, the leaves atrophy and take the shape of a crescent. It is difficult to get rid of this parasite, which develops especially when it is very hot.

The Olive Tree Psylla or Cotton

The psylla has sweet exudates that can induce fumagine. This insect is close to the aphid, attacks the flower. Its light green larvae live in colonies on young shoots and flower stems where they consume the sap by secreting a spectacular white flaky material but without danger for the olive tree.