For the past decade, the phenomenon of anomalous green fall of olives. This manifestation of abscission, which began to manifest itself for the first time in the northernmost areas, became pathological and gradually affected other Italian olive-growing areas, with not always equal levels of severity, not occurring in all years.
This 2023 is showing a worrying drop in some companies, with olive losses that reach and exceed 60%.
Usually the fall begins shortly after fruit set and continues until the core hardens, then stops.
The symptoms already appear with olives slightly larger than a peppercorn: a light first begins in the basal part color loss, which gradually darkens, some are created wrinkled depressions in the pulp, which reach the middle of the drupe, leaving the upper part green and turgid.
At the same time, the petiole, just under his attack with the branch, lose color: it turns from green to yellowish, narrows in the centre, losing volume. and a section of it is carried out, browning in the lymphatic vessels is highlighted. The pulp tissue below the petiole, in the calyx area, although green, it assumes spongy texture, forming a sinking of the tissues.
The olive can become all black or keep the top turgid and green; it can fall, perhaps favored by rain or wind, or remain on the tree, or detach just before the hardening time of the stone. Studies and research have been carried out over the years, which have led to evaluate multiple causes, such as the presence of fungal pathogens or the harmful action of the Asian bed bug. The University of Padua has identified the fungal species as the parasitic cause Botryosphaeria dothiodea, possibly joined and aggravated by another fungal parasite, the Diplodia olivarum, belonging to Botryosphaeriaceae. Other research institutes have also identified other fungal pathogens, such as Nothophoma quercina and Colletotrichum gloeosporioides, better known as olive leprosy.
These pathogenic fungi are considered opportunists, because they attack plants already subjected to stress and with little defense capacity. They are also known to cause deterioration of the woody organs, with the appearance of branch cankers, as well as to cause the premature fall of the olives.
As for the harmful action of the Asian bed bug it seems to be connected to its feeding activity, which is carried out with a biting and sucking mouthparts and equipped with a long rostrum, which the insect would insert into the olive, deepen it into the pulp, until it reached the still tender integuments of the stone . This trophic activity would cause tissue alterations, in fact, when cutting the olive, part of the pulp tissue shows blackening lumps.
However, the causes of the green drop of olives are not yet well clarified, they are probably connected to several factors, such as the action of fungal pathogens, with the contribution of insects such as Asian bed bug and do not exclude others, such as the Cecidomy. The biting and sucking action of these insects could well be a predisposing factor to fungal infections. There Asian bed bug, as well as other insects, could also be an inoculum vector of fungal pathogens, considering the possibility that it gets soiled with fungal inocula, which it would then transfer to the olive. In this, even if it has no scientific value, it has been observed that there was a concurrence of time between the establishment of the Asian bed bug and the appearance of the anomalous green olive drop.
defense strategies
To limit the damage caused by the anomalous drop, it is necessary to intervene in time, with a phytosanitary intervention plani, so as to gradually but significantly reduce the potential inoculum of pathogenic fungi.
The University of Padua has recommended this calendar of treatments:
1. at the vegetative restart, implement an intervention with Dodina-based products, at the doses indicated on the label, against peacock eye and olive leprosy;
2. in pre-flowering another intervention with Tebuconazole + Trifloxystrobin, always at the doses indicated on the label against peacock spot and olive leprosy;
3. once fruit set, carry out an intervention with Difenoconazole;
4. at the first enlargement of the olives repeat the intervention always with Difenoconazole, as indicated on the label against the Peacock's eye.
The possibility that the fungus or pathogenic fungi involved remain on the olive trees or on the infected drupes that have fallen to the ground, as they can be preserved until the following season, must be evaluated. It should also be considered that the increase in temperatures that have occurred in recent years could have made these mushrooms, which until a few years ago were little considered, as emerging and more insidious. As regards the containment of the Asian bug, if necessary, products based on Acetamiprid should be used.
AIPO Director
Interregional Association
Olive producers
