Listen to this article
Here are the main common pests that can affect olive trees and our recommendations to treat them.
Olive tree mite
We are going to see some of the organisms of animal origin that cause damage to the olive tree with some frequency. There are countless agents that are occasionally capable of constituting a plague in our olive groves, although most of the time they do not, but they constitute the food source of innumerable auxiliary insects that are our allies in the fight against pests.
They are tiny mites that are not visible to the naked eye.
They feed on the tender growing tissues damaging the buds, leaves, flowers and fruits. Symptoms are visualized when these organs are already of considerable development and size.
Olive tree mite (Aceria oleae)
This arthropod can cause damage to young leaves and fruits, but generally of little importance. In young olive groves, it can slow down growth quite a bit.
Attacks tend to occur in olive trees with excess nitrogen fertilization, irrigation and too many insecticide treatments that destroy the population of natural predators.
- Carry out phytosanitary treatments in a timely manner.
- Eliminate buds "suckers".
- Eliminate pruning debris.
- Control nitrogen fertilization. Watch out for excess nitrogen.
- Early checks, spring and summer are important, mainly from sprouting to after fruit set. Being more effective and reduce the chances of damage.
It is a moth that feeds exclusively on the olive tree, being present during all the seasons of the year, in one way or another.
The first generation (phylophagous) feeds on the leaves and shoots, acting mainly as a miner. The damages of this generation are only worrisome in young olive groves, since they damage the main shoots, slowing down growth.
The second generation feeds on the flowers, so it can influence the final number of fruit set. However, the olive tree produces many more flowers than it can turn into mature fruits, so the real damages of the antóphaga generation are very relative and are rarely of economic importance.
The carpophagous generation feeds on the olive seed. The moth lays the egg in the calyx of the fruit when it is freshly set, and when the larva is born, it penetrates into the bone. It spends all summer feeding on the almond, to emerge after metamorphosis as an adult in September, knocking down the olive when it comes out.
These damages are also of relative importance. Rarely does fruit drop per prays affect a high percentage of the harvest.
It must be taken into account that each time a fruit is removed from the olive tree, those that remain in the same fruitful shoot benefit and grow more.
When it comes to table olive groves, the fall occurs around harvest dates, and the fruits that remain on the tree do not have enough time to grow fat and compensate for the fall.
When the production of the farm is destined for the mill, and the harvest is carried out quite late, even more so with the olive tree with a high harvest, the fall of some fruits in September is offset by the fattening of the other fruits that remain on the shoot. , and there is hardly any economic impact.
Control of the pest is usually chemical, although when there are good populations of natural predators in the olive grove, the damage is considerably reduced. This situation occurs in the face of low insecticide pressure.
In the same way, olive groves that suffer in summer from high temperatures and water stress, have hardly any fall in September prays, since the larvae simply die dehydrated inside the fruit, and never emerge as moths or knock down the fruits.
In spring and summer there is an increase in the number of individuals due to the existence of high temperatures and the large amount of tender vegetative growth, susceptible to being attacked. During the day the butterflies are hidden on the underside of the leaves, perching with outstretched wings. They are active during twilight and night, being easy to capture with light traps.
The caterpillar feeds on the tender shoots of the olive tree, irreparably damaging the main bud.
It is a common pest in new plantations, where locally it can have some economic repercussion, by slowing down the development of young trees, since they have to sprout again through an auxiliary bud and continue with the growth of the sprout.
In adult olive groves, damage also occurs, but it is usually of little economic importance.
This pest mainly attacks olive trees with excess vigor due to excessive nitrogen and water inputs, so with balanced nutrition and irrigation, respecting the auxiliary fauna by not using insecticides, its incidence is greatly minimized.
Chemical treatment is carried out only if necessary and when enough damaged shoots begin to be visible, both in spring and early summer, and in autumn, when the maximum vegetative growth rates occur.
Olive weevil beetle
This beetle lives by day in burrows under the olive tree canopy. At night, it climbs the canopy and feeds on the leaves, leaving very characteristic marks.
Olive weevil beetle
These damages can be very serious in young seedlings, because they stop growth by drastically reducing the leaf / wood ratio and the leaf / root ratio. In adult olive groves, the damages usually go unnoticed.
The chemical treatment is complicated, because even when trying at night, the beetles fall to the ground when they perceive vibrations or light, not being sprayed with the insecticide.
It usually gives good results, applying powdered or granulated insecticide around the trunk, or covering the trunks with cloth bands, leaving the individuals trapped by their legs and dying during the day simply from dehydration and starvation.
Olive tree borer
It is a beetle that in its adulthood, throughout the summer, makes nutritional galleries in the armpits of small shoots, leaves and olives to feed itself. These galleries weaken and even dry the branches, leaves and olives. When it is windy or the olive tree vibrates, the branches at the base of which there is a nourishing gallery tend to break, causing the loss of many shoots and with them of production, both in the current year and in the following years.
Olive tree borer
The adults make their spawns during the spring, in olive wood whose sap transit is stopped, such as a young tree damaged by ice or a branch broken by the wind, but above all, the branches cut in the pruning. Larvae develop in these woods, emerging in early summer as adults, causing the aforementioned damage.
Adults are bad fliers, therefore the damage is very restricted to areas close to where there are pruning remains. The damage usually occurs near homes and urban centers where olive wood is stored.
The main control measure consists of eliminating the pruning remains as soon as possible in spring, or keeping them airtight, so that the adults cannot access the firewood to make their laying, from which the adults would later come out that would damage the nearby olive trees.
When you are in an area where damage is common, chemical control will be carried out, treating when the olives are freshly set, a moment that coincides with the peak of adults leaving the wood.
It is the olive grove pest that causes the most economic damage. Although it does not damage the olive tree at all, it does cause considerable damage to the fruits, reducing both the quantity and quality of the harvest.
The larvae consume a significant percentage of the olive pulp, which means a considerable reduction in the weight of the fruits and therefore of the harvest. However, the greatest damage that the olive fly larvae does, is not this.
When the larva finishes its development, it emerges either to pupate in the ground, or as an adult, to the outside through a hole. Through this hole, fungal spores and moisture will enter the interior of the fruit. The more time passes from the appearance of the exit hole in the olive, the more the fruit will deteriorate inside, and the worse the chemical and organoleptic characteristics will have the oil. In the case of table olives, it makes them totally useless.
At the end of autumn, in the olive grove we find both adults from previous generations, as well as larvae in the fruits. These latter larvae usually overwinter as pupae in the ground. In areas with very cold winters, winter mortality of both adults and pupae is high, but with mild winters, such as on the coast, many live individuals arrive the following spring.
In spring, the new generation of olive fly resumes activity. They will feed during the spring and summer on sugary substances, such as flower nectar or fruit juices. Therefore, environments with a lot of vegetation and fruit trees are favorable for the presence of the olive fly.
Temperature and humidity in summer are the main limiting factor for the olive fly. From 35ºC, the activity and survival of adults plummets. Therefore, the interannual incidence of the fly in each plot is well explained by the microclimate and habitat close to the olive grove.
Areas in which in summer there are few shades, little water, little fruit and very high temperatures, such as most of the productive areas of southern Spain, are not prone to the life of the olive fly.
On the other hand, in coastal or mountain areas, with numerous watercourses, orchards, fruit trees, and especially shadows, flies survive the summer well and therefore the incidence will be high.
The reproductive activity of the olive fly occurs between hardening of the bone and veraison. When temperatures are below 35ºC, the female fly is capable of laying fertile eggs. Above this temperature, there are no viable clutches. The female fly makes its lay in the following way: it feels the fruits with its oviscapto, to lay an egg in the fruits that it likes, which will be those that are not suffering from water stress and have a good growth and maturation rate.
These bites are the best way to monitor fly activity on our farm.
However, the fact that there are bites, does not mean that the fly is laying eggs in the fruits. The bites do not leave eggs if the temperatures are too high or if the fruit is not to the liking of the fly, because it is too green or too dehydrated. The number of bites only indicates the number of active female flies there are. To find out if the bites are fertile, we simply cut a piece of flesh from the fruit around the bite, and thus we can see if larval development has begun by viewing the nutritional gallery.
As the summer progresses, the daily thermal integral decreases. In parallel, the olives are gaining thickness. The percentage of bite with fertile egg, will be increasing.
From the first bites, after a few weeks, the first generation of flies of the campaign emerge. From this moment on, the bite rate increases exponentially, as generations of adult flies overlap. If the olives in summer suffer from water stress, they are not attacked by the fly. If the olive tree has a high harvest, the olives are hard and green, and they are less attacked.
Normally, the table varieties, or the thicker ones, with sweeter and less bitter fruits, are preferred by the fly. Therefore, in olive trees with medium or low harvests, of thick-fruited varieties, with mild summers, it is where we must pay more attention to the fly.
As winter approaches, activity decreases, decreasing in cold areas and not disappearing in warm coastal areas.
There are various control measures, but almost always with limited effectiveness.
The first thing would be to ensure that the fruits are the least palatable for the fly. This is achieved by restricting irrigation in summer, or treating our olive trees with kaolin or diatomaceous earth.
The chemical control strategies would be, on the one hand, patching or treatment in bands, and within the total treatments, adulticides and larvicides.
The patching consists of applying small spots of a mixture of attractant with insecticide in specific points of the crown of some olive trees on the farm. The flies will go to feed on these spots, and they will die shortly after, thus reducing the adult population and therefore the bite.
This system is inexpensive and respects the auxiliary fauna, so it is a good control strategy if it is applied as soon as activity is detected in early or mid-summer. There are even insecticides for use in organic farming, which are also being used in conventional agriculture.
Another modality of patching would be the treatment in bands with light aircraft, which is carried out in large areas by farmers' associations, and has very good efficacy. Today in many areas this treatment is carried out in bands with insecticides authorized in organic farming.
Traps with attractants can also be used, which work in a similar way to patching, and are the most used control method in organic farming.
When you choose to treat the entire olive tree canopy, it can be treated with an adulticidal or larvicidal approach. Adulticidal treatments reduce, similar to patching, the adult population, and thus bites. Insecticides with low environmental impact and short-term safety are often used, such as pyrethroids. However, if bites have already occurred, this treatment is not effective because the larvae continue to develop and will therefore deteriorate the fruits.
When there is already a large percentage of chopped olives with larvae, the total larvicidal treatment is the best option. The insecticides used for this purpose are systemic and have a high impact on auxiliary fauna, so this option is convenient to use only as a last resort.
The different control modalities can also be combined in the same campaign and farm, depending on the situation.
A passive measure to reduce fly damage would be early harvesting. The deterioration of the chopped fruit is progressive throughout the autumn and winter, so if early harvests are made, the quality of the oil obtained is hardly affected.
Therefore, in areas with a high incidence of flies, early harvesting makes it possible to continue obtaining good quality oils, bearing in mind that the other control measures will be 100% successful, and there will always be chopped fruits.