There is extreme variability in olive production from one year to the other and there are indeed many different threats to olive growing. But the biggest threat is being underestimated: climate change and global warming.
Alarmism … not always sustained by evidence
From year to year, the dangers for olive growing are multiplying. The alarmisms on the production of extra virgin olive oil are more than founded, however they are not always so on the spread of diseases and parasites. Undoubtedly there are still considerable dangers that threaten the health of olive trees: among these is Bactrocera oleae, more commonly known as olive fly,
which thrives in wet environments. This causes browning and sudden changes in color of the olive surface, usually localized. This rot, although localized, affects the quality of the olive and the oil derived from it.
The latest alarm comes from northern Italy and is generated by the appearance of the Asian bug. This insect causes some very similar damages to that of the olive fly. In this case, the browned part can be cut with a small knife to notice that it is completely rotten inside, even though it doesn’t show erosions or galleries. This polyphagous insect, coming from the far east, manages to reproduce copiously not being opposed by antagonist insects. Although negotiations have begun to bring its natural antagonist to Italy, the samurai wasp, the process seems to be still long. The damage of the bug could be amplified in the case of trees already destabilized.
The real danger: climate change
More than founded, it should be alarmism on climate change. In fact, the biggest problem is not the effect of individual diseases and pests, but a set of factors that contribute to weaken the plant’s immune system. The causes of this progressive weakening of the ability of plants to react is also due to climate change.
Climate change produces significant damage, especially in neglected or abandoned olive groves, where the lack of care causes a greater probability of proliferation of pathogens. The olive tree, in itself, does not need excessive care. That is why so many olive growers continue to pursue a very mild type of cultivation, many almost tended to dispose of their olive groves. These cultivation techniques are no longer sustainable. Olive trees need more care to cope with unusual temperatures. The olive groves, labeled “L’Olio dei Sassi”, receive constant care throughout the year to cope with hot summers, harsh winters and mid-seasons with turbulent storms.
The professor. Marracchi, an internationally renowned climatologist, repeatedly highlighted the importance of the effects of climate change. According to his studies, a progressive tropicalization of the Mediterranean climate is taking place. The regions of southern Europe, and even more so the regions of southern Italy, are the most interested ones. More tropical climates are due to the displacement of the hadley cell (climate zone traditionally located in the tropics) towards the north. This leads to a remarkable mutability of climatic phenomena: elevated temperatures, flared seasons, extreme climatic conditions.
The olive tree is a plant that adapts well to different temperatures, nevertheless it still needs adequate availability of water, light and heat. These are, in fact, three very important components for maintaining a good health of the plant and, subsequently, for a satisfactory production: too much or too little rain can have harmful effects. Excesses or limitations involve a greater sensitivity to diseases (peacock’s eye, leprosy, etc.), a considerable reduction in the weight of the drupes and changes in the sensory composition.
The risk of prompt temperature changes represents another source of uncertainty for olive growers.
An excess of heat leads to lack of water in the plant. For these reasons, the olive behaves similarly to howt we would if we were in the desert for a long time: it reduces its physiological activities waiting for better times. However, a prolonged reduction in physiological activity weakens the plant, which is thus more susceptible to attacks by pests and diseases. On the contrary, too low temperatures could cause damage in the early period (late autumn for plants not yet acclimatized), in full winter in case of too rigid temperatures and high percentage of humidity, and in early spring for early plants.
The effects of thermal rise
A Spanish study has tested the behavior of olive trees in conditions of temperatures raised by 4 ° C. By creating “Open Top Chambers”, Spanish researchers have been able to observe the effects of thermal rise. The greatest effects have been observed on flowering and fruit set (phase of transformation of flowers into fruits). In particular, an extension of the flowering phase has occurred: this is a potentially risky phenomenon as it exposes the plants to cold returns that could damage, if not even, burn the flowers with negative consequences on the percentage of fruit setting and on the next production. High temperatures have established a deficit water status in the plant that has reduced the percentage of setting, the number of drupes (fruits). Moreover, in the three years of observation, an advance of the veraison between 17 and 30 days was noticed accompanied, however, by a phase of maturation- in which there is the accumulation of oil in the drupe- slower with a reduction in the percentage of oil of about 30%.
In addition to this, there was also a significant reduction in oil yield, about 60 / 70%, due to the abortion of fruit trees during the setting phase.
However, it is interesting to note that raised temperatures have led to greater vegetative growth of the branches and the diameter of the trunk.
As we have seen, scenarios of generally higher temperatures, even of a few degrees, bring with them important consequences for Italian and international olive groves. Rising temperatures would affect the plant’s need to “vernalize” (feel cold during the winter). Even excessive moisture creates an extremely favorable environment for the attack of pests, as it is to create a sort of wet layer on the olives which benefits insects and fungal diseases (peacock eye, cercospora, etc.).
Even though we keep underestimating the destructive risks of continuous thermal rise, many scholars and expert agronomists continue to fear scenarios of complete redefinition of the Mediterranean olive growing landscape. According to some of these, it will even be possible to see a shift towards the north of the olive production line by 2050.