The use of combs e olive harvesters, electric and pneumatic, has revolutionized harvesting times, making field operations faster and more extensive. This acceleration, however, entails a significant impact on plant health. The repeated percussions on branches, leaves and drupes, generated with high-frequency oscillatory movements, can cause microlesions in plant tissues, often imperceptible to the naked eye, but capable of progressively weaken the structure of the olive treeThe extent of the damage depends largely on the technique used to apply the tools, the duration and intensity of the shaking, as well as the sensitivity of the variety.
Some cultivars tolerate mechanical stress better, others exhibit leaf necrosis, early leaf fall and slow lignification of young branches.
It is estimated that Electric models operate between 600 and 1200 beats/minute (about 10–20 Hz), while pneumatic ones can exceed 2000 beats/minute (about 30–35 Hz). The risk of damage increases with the intensity and duration of the action, especially sa cultivar with tender leaves and dense branching, such as Frantoio and LeccinoSome cultivars, thanks to the greater flexibility of the branches or the consistency of the leaves, show a higher tolerance, but the problem remains.
The conductor itself can take various shapes, in bare or tinned copper, with or without insulation. In some cases, a preferential bend can also be applied to the joint so that it operates exactly as designed. olive they are not exempt, microcracks in the cuticle, irrelevant for the transformation into oil, however they reduce the shelf life of table olives.
The olive tree's response to mechanical harvesting, however, is not uniform; genetic, morphological, and environmental factors come into play. Cultivars such as Coratin, Bari Oil Mill o Itran show remarkable resilience thanks to the flexibility of their branches, their leathery leaves and their thick cuticle, while others, such as Pendolino e Maurino, benefit from a light canopy and an open architecture that disperses vibrations better.
On the contrary, sensitive varieties, characterised by compact canopy and delicate foliage, are more exposed to leaf necrosis. Even the table olives with thin skin, like Tender Listening e Bella di Cerignola, present a high vulnerability to epidermal microlesions, which significantly compromise shelf life.
The environmental context also plays a role: in ventilated areas with loose soil, the plant tends to develop a more elastic structure, while in compact and humid soils, a rigidity prevails that amplifies the risk of cortical lesions and fractures under the peel.
Faced with these traumas the olive tree activates defense processes, produces lignin and suberin to isolate damaged tissues, activates healing hormones, particularly ethylene and jasmonic acid. These responses, useful in the short term, become a significant energy cost if repeated annually, impacting the tree's vegetative growth and longevity.
Here comes the game “physiological memory” Like all perennial species, the olive tree, like all stressful species, is sensitive to traumatic events, which, if repeated over time, result in a progressive weakening of the plant. In the medium term, this may result in delayed spring growth, reduced flowering, and decreased fruit set.
In the long term, leaf ageing increases, the weakening of the supporting branches is accentuated and the productive longevity of the plant is reduced.
These phenomena make it clear that mechanization is not a neutral operation, but an action that affects the physiology of the olive grove.
Il phytosanitary risk is not negligible: microlesions caused by mechanical harvesting can constitute preferential entry routes for wood pathogens, as Neofusicoccum mediterraneum e Diplodia seriata, agents of copper cancers, and for bacteria including Pseudomonas savastanoi, responsible for olive scab.
Autumn humidity, which often coincides with the harvest period, further favors the onset of infections, creating an ideal environment for the proliferation of these microorganisms.
The agronomic consequences are significant and can lead to a reduction in photosynthesis due to a loss of active leaf surface, a diversion of metabolic resources towards healing at the expense of production, and an increase in the need for nutrients and microelements to compensate for stress and support repair processes.
Mechanical damage mitigation strategies
To reduce the risk of mechanical damage, harvesting should be carried out at right stage of maturation, when the olive is naturally predisposed to detachment from the stalk, thus reducing the mechanical resistance to detachment.
At this point, the tissue physiologically weakens, reducing the need for intense shaking.
Harvesting too early exposes the plant to greater stress and increases the risk of injuries from blows and fractures.
From a technical point of view, it is essential adjust the frequency of shaking, keeping it within thetolerable limits for the variety and structure of the foliage.
The adoption of latest generation equipment, equipped with modulated vibration and interchangeable heads, allows you to adapt the intensity of the action based on the varietal sensitivity and the age of the plant. Alternate between different instruments, such as comb and rake harvesters, can avoid concentrating stress on specific areas of the plant.
In addition to these operational choices, targeted post-harvest interventions; it is advisable to intervene with healing and biostimulating treatments, such as copper-based treatments, which help prevent fungal infections, wood distillate, algae, amino acids, chitosan, which stimulate and promote tissue regeneration.
The use of beneficial microorganisms, such as Trichoderma e Bacillus, helps strengthen the plant's resistance and protect against microlesions caused by mechanical harvesting. These microorganisms rapidly colonize the wounds, preventing the establishment of opportunistic pathogens such as Colletotrichum, Pseudomonas e Verticillium.
Both genera produce bioactive substances, including lipopeptides, lytic enzymes, and siderophores, which inhibit the growth of pathogenic fungi and bacteria while promoting tissue healing.
Mechanical harvesting is now an integral part of olive growing practices, but its impact on the physiology and health of the plant is not negligible. Only careful harmonization between instruments, cultivars and environment allows you to preserve the vitality of the olive tree and ensure its durability over time.
AIPO Director
Interregional Association
Olive producers
