Like what happens with all crops, decades of specialisation and growing monocrops have made olive tree pests proliferate and are making them increasingly more resilient. This can put the entire plantation at risk.
How do I know if an olive tree has a pest?
In general, you’ve got to be highly alert to any changes that take place on the trunk, leaves or fruits to detect the presence of diseases on the olive tree. Pests tend to attack the roots, leaves, flowers and/or fruits. If you notice changes in these areas, in all likelihood the tree has a pest, although you also need to consider the general overall condition of the tree.
In these cases, the first step is to act quickly and determine the source of the problem. After you’ve decided on the type of pest, you should assess the risk to the tree and to the rest of the crop. In general, when a good harvest is expected, the use of insecticides is not recommended, although this depends on many factors, such as the state and age of the olive trees and the type of disease.
Below, we give you a guide to the most common olive tree diseases and how to recognise and handle them.
Most common olive tree pests
Olive fruit fly (Bactrocera oleae)
This infestation of insects is the most common that can affect olive trees. Fruit flies feed on the olives before they are completely ripe. They lay eggs on the fruits, where mild temperatures and abundant rainfall favour their proliferation. Conversely, an increase in temperatures affects the flies and retards the proper development of the larvae.
As they are flies, there are a wide range of treatments: chemical products, diverse traps (pheromone, coloured or chemotrophic) or, even, homemade traps like those traditionally used to combat other types of flies.
Olive moth (Prays oleae)
This disease is a perfect example of how the pest has gradually adapted to the crop to become increasingly more resistant. There are normally three generations a year of the moths:
- Phyllophagous: the first generation affects the leaves and buds
- Anthophagous: the second generation attacks the flowers
- Carpophagous: the third generation focuses on the fruits
This pest can therefore be highly damaging to farmers, especially the third generation. However, we must remember that in specific years this pest can become an ally. Olive trees, like so many other fruit trees, produce more flowers and fruits than they can subsequently develop. In other words, if the moths did not eat them, they would still be eliminated before the olive develops.
If there is a very high presence or the crop is at risk, there are several chemical treatments to control or eradicate the infestation. High summer temperatures also help to combat the presence of the olive moth.
Olive weevil
This infestation of beetles, while having little impact on traditional olive groves, can entail a true problem during the development phases at new plantations due to the products that are generally used and the more intensive processes. They tend to appear in the autumn, feeding from the tree leaves, laying their eggs and disappearing in the winter. With the generalised increase in temperatures, these cycles have modified and now the adult specimens spend more time feeding before laying eggs.
Poisons and insecticide products have increasingly less effect on this pest. The best solution is a traditional barrier method: roll adhesive strips or synthetic fibre – like the filling of a cushion – around the trunk so that the weevil cannot reach the leaves.
Olive soft scale or black scale (Saissetia oleae)
This pest can be extremely serious, not so much due to the effect it can have on the tree, but because it is usually accompanied by other pests and diseases. Scales feed on the olive tree sap and secrete a sticky substance onto the leaves like a treacle.
In turn, this substance attracts the grey knight or dirty tricholoma, a mushroom that is one of the most common olive tree diseases, and ants, which feed on this secretion. In fact, the ants have often been seen protecting and helping the olive soft-scale pests. In this sense, a very high presence of ants on the crop may be an indicator of the pest.
Olive psyllid
This pest is easily recognisable because an endless number of tiny whitish insects appear on the leaves and branches. Despite how eye-catching they may be, they fortunately do not usually cause severe damage, and no treatment needs to be followed.
Olive bark beetle (Phloeotribus Scarabaeoides)
In principle, this insect does not represent a significant risk to the tree either, although it is advisable to control it because if the population increases excessively, it can cause serious damage. This pest digs galleries into the olive tree bark, cutting off the flow of sap and drying out the branches.
To eliminate this pest, traditional mechanisms usually work very well, such as pruning the infected branches and then burning them to break the cycle.
Moles, rabbits and other rodents
In addition to insects, small mammals that make their dens among the tree roots can also become a pest for olive groves, and can even dry out entire trees, with no cure. The best way to prevent the damage from becoming irreversible is to plough the field to put an end to their underground galleries.