Tag Archives: plant diseases

Tree diseases harm people too

surano

An olive grove in Surano, Italy, following infection by Xylella fastidiosa. Wikimedia Commons CC BY-SA 4.0 Sjor

In the midst of a global pandemic, expressing concern about trees can feel like an indulgence. That’s not to say that COVID-19 is foremost on everyone’s minds. For farmers in East Africa about to face another devastating plague of locusts, or those in Vanuatu whose homes were destroyed by Cyclone Harold, there are more pressing concerns. On our own doorstep there are many people going without food in the UK, one of the world’s richest countries. Even climate change is having to take a back seat for the time being.

And so you might find it hard to spare any thought for a disease which is quickly sweeping through Mediterranean olive trees. For those of us living in northern Europe the direct impact is likely to be felt as increased prices for olives and olive oil, and perhaps even some scarcity in the next few years. I’m sure your heart bleeds for the middle classes.

Many people don’t have the luxury of shrugging this calamity off though. And it truly is a calamity for producers in some of the poorest regions of Europe, particularly in rural parts of Italy, Greece and Spain where olives and other orchard crops have been the mainstay of livelihoods for generations. They are about to face not only a pandemic, but the prolonged recession that will be its aftermath, in which their whole way of life will simultaneously be disappearing. A new paper estimates that the total economic impact of this disease could exceed €5B*. It isn’t just about the trees.

This was a disaster that could so easily have been avoided. The pathogen Xylella fastidiosa was first recorded in olive trees in southern Italy back in 2013. It likely arrived from Central America where similar pests are endemic, probably via the horticultural trade. National and international agencies rapidly responded, and a containment plan was put in place, agreed with both the Italian government and European Commission. This was beset with protests and legal challenges which delayed any action. Amazingly, several scientists and public officials were accused of deliberately spreading the disease and subjected to a police investigation**. All this wasted valuable time.

By 2016 the disease had already reached Spain and southern France. Now it’s also been detected in Portugal and Israel. Unfortunately it appears that trees can be asymptomatic for some time, which has made tracking and modelling its spread more problematic. It can also infect a range of other trees, including common orchard species like cherries, almonds and plums. These are often asymptomatic hosts though, which means that the disease can spread across landscapes undetected, carried by common xylem-sucking insects. Now that the disease is at large across Europe, local containment might be possible in some regions, but a full outbreak is almost inevitable.

The new paper by Schneider et al. suggests that constant vigilance, which means routine testing and reporting of cases, should be combined with measures to reduce the rate of spread, such as felling of trees in buffer zones and vector control. This may buy enough time for resistant trees to be developed and planted, or for a transition to substitute crops. To do so requires trust and co-operation between government agencies and individual landowners, something that has thus far been in short supply. It also inevitably means that some farmers will have to sacrifice healthy orchards for the good of others.

Whatever the outcome, the landscape of large parts of the Mediterranean looks set to change dramatically in the coming years. And all because we failed to act even when the evidence was in place. Will we learn the lessons for next time?

 


 

* Roughly equivalent to $5.5B or £4.5B at time of writing, but have you seen how crazy FOREX markets are at the moment? Oddly some of the media coverage has talked about a figure of €20B, which wasn’t the headline figure of the original paper, but appears to be based on adding up all the largest estimates and assuming a worst-imaginable scenario.

** Italy has previous form when it comes to prosecuting scientists and officials whose advice is not approved of.