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Passerine olives, causes and remedies


After telling you about theolive fly, we continue to deal witholive tree diseasesand we do it by talking about the so-called "passerine olives", of thevery small oliveswhich do not correspond to a variety but are the synthesis of a pollination defect.

When it comes topasserine olives, reference is made to the defect ofblanching of the oliveswhich causes a significant loss of production. Thepasserine olivesare better definedpsudodrupe, small rounded olives, grouped in clusters which, although provided with a stone, do not have seeds. In theolive, the phenomenon ofpseudodrupe(passerine olivesor blanching of the olives), is attributable to a difficulty in fertilization by pollen. This difficulty can be caused by several factors, among them there is a lack of boron.

Passerine olives, causes

How are passerine olives formed?
The formation ofpasserine olivesit is determined by a defect in pollination. Specifically, the pollen tube enters the stigma but without reaching the egg; its presence does not cause pollination but stimulates an enlargement of the ovary with effects comparable to those induced by parthenocarpy (fruit production without fertilization). The result is the formation ofpseudodrupe, more commonly calledpasserine olives.

The causes that lead to this pollination error are many. The flowering of the olive tree is a long process in which climatic events can occur which, through various mechanisms, can reduce production or damage the crop. We have already seen how temperatures and humidity can affect the olive harvest through the development of the Bactrocera oleae fly; now we will see other consequences of climatic conditions during flowering:

  • Late colds can damage the tissues of growing flowers and cause the formation ofpseudodrupe. This is because, if temperatures drop below freezing during the spring, the flower organs can be seriously damaged.
  • Dry winds (whether hot or cold), can reduce the receptivity of the stigma by drying it up (when the flowers are open), just as high temperatures can cause it to dry out quickly. As is clear, the lack of humidity can lead to a slowdown in the growth of the pollen tube with consequent formation ofpasserine olives.
  • An excess of humidity in the air can also trigger the formation process ofpasserine olives.This is because high humidity levels hinder the spread of pollen.

Deficiencies of boron in the soil can also lead to the formation ofpseudodrupe.

How to prevent the formation of passerine olives
To avoid the formation of those very small olivesdifferent strategies can be implemented.

Foliar treatments based on boron
First of all, you should do a soil analysis: if there are boron deficiencies, it will be possible to carry out boron-based foliar treatments that will be performed between late winter and early spring.

Other precautions
Carefully observe the beginning and duration of flowering, paying maximum attention to the period in which the flowers are fully open, at this point you must check two things: compatibility of pollination between varieties and duration of pollination.

If the period when the flowers are fully open is too short (2-3 days), fertilization may not have occurred naturally. In this case, the only possible intervention is rather mild and consists in wetting the hair with water during the evening hours, thus attempting to prolong the vitality of the gametes.

Make sure you have compatible varieties for cross-pollination: in the case of non-overlapping of the blooms (one variety blooms when the flowers of the other are already closed), it is possible to try the grafting of some other variety.



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