The olive tree can survive in a dry climate, nevertheless, an adequate water supply is essential at certain times of its vegetative cycle. During Summer the fruit is in its early stages of growth development, the pits harden, the fruit grows until the moment when the green color of the skin fades and reddish spots appear. During these stages a lack of water causes the fruit to be smaller, its oil content lower, and it may fall from the tree.
In this period olives are exposed to all the damages caused by harsh weather, by disease or parasites. A very good harvest might be seriously jeopardized by these factors.
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Control of the Olive Fly
The Olive Fly (Dacus olei) is the most feared enemy: in certain years this insect can destroy the entire crop. It is present in every area of the planet where wild and cultivated plants of the "Olea" genus are found: in the Mediterranean, in southern and eastern Africa and in Asia (as far as India).
In a single year seven or more generations can develop; larvae emerge from the eggs laid in the olives, they feed on the pulp, pierce it and fly away. In the years when cold winters, hot summers or predators fail to limit the number of flies, each harvested olive may be marred by holes and grooves, making it useless for both table and oil use.
The war against flies is fought with antiparasitics, poisoned bait and, recently, biological methods, which consist in spreading a few species of parasites of the olive fly that attack its larvae during summer.
 The enemies of the olive tree - Color table, France, second half of the 19th century
The wood, leaves and fruit of the olive tree are subject to attack by many parasites that have been the object of study by agronomists and botanists since the Roman period.
Irrigation
This practice is usually limited to recent olive groves. Most of them get through the Summer months without irrigation, thus they face the consequences of drought: fruit falls, ripening is slowed, the fully productive years are rarer.
Regularly irrigated plants can double the volume of fruit. The most common irrigation systems change by areas, and therefore in relation to the volume of water available, the flow rate, water supply costs, the orography of the area, the size of the area to be irrigated. The traditional systems (basin irrigation, furrow irrigation, flow irrigation) exploit the gradients of the ground, by using ditches and furrows carefully arranged and rigorously controlled.
More modern methods allow the irrigation of narrow spaces near the plant through a drip system.
Plastic pipes with nozzles at varying distances supply measured amounts of water (from 2 to 10 liters ( 2.1 to 10,6 quarts) per hour), thus meeting the needs of the plant with a saving of 10% to 30% compared to traditional methods.
Drip irrigation plant - Tuscany
This system is used principally in new olive groves, that are supplied with adequate plastic pipes and irrigation equipment.
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