Fruit trees are generally exposed to many pests, that endanger their existence. The olive tree is very robust by nature. The body, the leaves and the fruit are very bitter. Because of its bitterness it is less exposed to insects and animals, especially when it is planned on hills and mountain sides.
One of the most dangerous enemies of the olive tree is the black scale. It is an insect that loves olive trees and orange trees. These insects stick themselves to the olive branches, leaving behind them a black trail of dust, formed by the fluid they extract from the tree and their droppings. The wind spreads the dust all over and covers the branch.
Riondet tells us that during the winter, when the young insects are still under their mother’s body, getting protected from the weather and their mother is already dead; they can get crushed by robbing the branches with a brush dipped into vinegar.
Lardier and Reynaud both recommend to sprinkle the tree with lime water.
Du Breuil also confirms that rubbing and spraying will destroy the insects and their black trails.
Olive growers are aware of the danger of these insects and are acting accordingly. Ignorance and neglect can bring a small olive oil production and tiny and underdeveloped fruit. Also can kill production and tree completely.
There are other insects that are not so important, that attack the olive tree. When the olive grower keeps his eyes open and takes action to face the enemy when it makes its appearance, there is nothing to be feared.
Many times Mother Nature comes to the rescue of human errors and carelessness. If an insect scientifically known as Hylesinus oleae, causes the branches to break when heavy winds occur and if a fly called dacus oleae, deposits its eggs on the fruit of the olive and afterwards feeds on the olive, the aunt and other carnivorous insects come and feed on them.
Pruning is the best preventive, so light and air can get in all parts of the tree and spray the whole tree with lime water. A very small portion will survive and that is going to be destroyed with the help of a greater force, the Mother Nature.
The olive fruit fly and the Mediterranean fly are the two other dangerous insects that attack the olive fruit and can cause serious damage. Both are considered very damaging pests for the olives, in Southern Europe, Middle East and North Africa. Most of the damage appears in the fall, between September and October.
The olive flies lay their eggs under the skin of the olive fruit and the caterpillar that comes from the eggs, feeds from the olive fruit flesh, leaving behind a track of brown tunnels. The effected olives appear to have brown spots, but when they are cut open, you can see brown tunnels and also maggots. The olive oil that comes from these effected olives, is high in acidity and the flavors are unpleasant and extra virgin olive oil is out of the question.
A certain type of caterpillar, called lepidopterous caterpillar, feeds on the leaves and flowers. Another serious enemy of the olive tree is the rabbit. It eats the bark of the olive tree and the result is that the tree is most likely to die.
Du Breuil tells us that another dangerous enemy of the olive tree is the excessive cold of some winters in Europe, when the thermometer reaches -12 degrees C. From the mid 1700 until the end of 1800 the olive trees have been frozen on an average of ten years.
California is a place where the thermometer doesn’t fall below -2 degrees C or 28 Fahrenheit, where the olive tree will stand without danger. This is a good reason why the cultivation of the olive tree should be adopted fearlessly and extensively. The climate in California is ideal for olives and olive oil production. Californian olive oils are of great quality and equal to European ones.