There is a word that, in Puglia, has almost become an emotional switch: xylella. You say it and the conversation changes tone. For years the dominant story has been simple, perhaps too simple: desiccation equals bacterium, bacterium equals killing, killing equals “there is no alternative”. Except that science rarely delivers linear fairy tales.
A study published in 2026 in the scientific journal Agriculture reopens a question that in Puglia is anything but theoretical: does it make sense to continue cutting down even healthy trees just because they are within fifty meters of a positive plant, when the numbers tell a much more nuanced reality?
A much lower presence of xylella than is believed
The work starts from the data collected in the areas subjected to phytosanitary monitoring, those where controls are systematic and on a large scale. Not sporadic observations, but campaigns that involve tens of thousands of olive trees every year. And it is precisely here that the first element of discontinuity emerges.
Between 2020 and 2022, the overall percentage of trees testing positive for Xylella in containment areas and buffer zones was less than 1%, with values as low as 0.06% in some cases. Striking numbers, especially when compared with the quantity of plants which, despite showing symptoms of desiccation, do not test positive for the bacterium.
In epidemiology, such a low correlation forces us to stop. Not to deny the existence of the problem, but to avoid attributing to a single factor a phenomenon which, in reality, appears more complex. If most of the olive trees that dry out do not harbor the bacterium, then the question becomes inevitable: what else is contributing to the collapse of the trees?
Desiccation is not a unique disease but a complex syndrome
The study insists on a point often forgotten in the public debate: we are talking about rapid olive tree desiccation syndrome, not a disease with a single cause. And a syndrome, by definition, arises from the interaction of multiple factors.
Alongside xylella, aggressive phytopathogenic fungi have frequently been isolated in the affected areas, capable of producing very similar symptoms and, in some cases, leading to the collapse of the tree much more quickly. Added to this are environmental elements that are anything but marginal: prolonged drought, high summer temperatures, sudden rains, discontinuous agronomic management and decades of intensive use of herbicides that have impoverished the soil.
The result is a fragile system, where the tree comes into stress and becomes more vulnerable to everything. In this context, reducing the entire crisis to a single pathogen risks being not only scientifically incorrect, but also ineffective on a practical level.
The 50 meter rule is the most critical point
The most delicate heart of the study concerns the so-called 50 meter rule, which requires the felling of all host plants around a positive olive tree, regardless of whether they are healthy. A measure designed to block the spread, but which, in light of the most recent data, is being questioned.
According to the epidemiological analysis cited in the work, asymptomatic trees have a very low, if not negligible, capacity to spread the bacterium. In buffer zones, trees around a positive plant often show no symptoms and, after testing, test negative. Yet they are eliminated anyway.
The proposal put forward is simple, at least on paper: test first and cut down only the actually positive plants, leaving the healthy ones standing, even if they are within a fifty meter radius. A choice that does not eliminate the risk, but avoids needlessly destroying trees that do not represent a real threat.
The study also recalls a detail that weighs more than many theories: some olive trees that tested positive years ago, but were not cut down due to legal disputes, are still alive and without symptoms, as are the surrounding trees. A fact that, at least, deserves to be observed without prejudice.
Check the carrier and reduce the bacterial load
If the bacterium moves thanks to an insect vector, the most effective strategy is not to chase healthy trees, but to reduce the presence of the vector itself. The study highlights how the control of the initial phases of the insect cycle, eggs and juvenile forms, is much more effective than late interventions on adults.
At the same time, evidence is reported on treatments capable of reducing the bacterial load in the foliage, allowing the trees to continue producing. We are not talking about a “miracle cure”, but about agronomic and phytosanitary management aimed at containing the problem, not erasing it with a chainsaw.
Destroying healthy trees is not a strategy
Perhaps the most honest point of the study is also the most difficult to accept: reducing the risk to zero is not realistic. The vector can also move long distances and the bacterium can find host in plants other than the olive tree. This means that isolated outbreaks will probably continue to appear, even outside the already demarcated areas.
In this scenario, continuing with automatic and indiscriminate killing risks turning into a permanent strategy of destruction, without a real increase in safety. The study does not propose shortcuts, but invites us to change our approach, based on the most up-to-date data and more targeted management.
Looking at the numbers, in this case, does not mean minimizing the problem. It means avoiding that, in the attempt to control it, we continue to lose healthy trees, landscape and scientific credibility.
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