Fresh Ideas: Deadly bacteria killing Italy’s olive trees

The bacterium xylella fastidiosa was first detected in the olive trees of southern Italy in mid-October of 2013, although U.S. scientists at the University of California Berkeley together with an entomologist from the U.S. Department of Agriculture speculate given the size of the area infected, the introduction of the bacteria occurred as many as 10 or more years ago.

By the beginning of 2015, one million olive trees were diseased in the Italian region of Puglia (Apulia in English), the heel of Italy’s boot. Since Puglia alone accounts for 40 percent of Italy’s olive oil production, the infestation is serious. Because the bacterium is insidious and deadly it does not bode well for the remaining 59 million olive trees in Italy.

You may have heard about this bacterium causing Pierce’s disease in Napa or Sonoma vineyards, afflicting fruit or nut trees in the southern U.S. and elms, oaks, and sycamores as well. Often referred to as BLS (bacterial leaf spread), it’s generally speaking an infectious, chronic disease transmitted by insects which colonize and “clog” a tree’s water conducting tissues, disrupting water transport in roots, branches, and leaves. It has a wide “host plant range” (meaning more than 200 plant species are susceptible to the disease). There’s no cure, therapy, or prevention.

For years the bacterium xf (abbreviation for xylella fastidiosa) was confined to the Americas. In 1994, it was noticed in Asia and in the 2000s there were reports of Pierce’s disease in Taiwanese vineyards. But it had never been detected in Europe. Today, it’s not only found in Italy, but on the island of Corsica and in southern France.

The discovery of xf in Italy’s olive groves is especially alarming because the host tree experiences “quick decline symptoms.” Consequently, last year three thousand infected olive trees were cut down in order to create a sanitary buffer between the infected and still healthy trees. And this is only the beginning. In the meantime, the price of olive oil has already risen 20 percent.

For those who wonder how xf made its way to Europe, the scientists at UC Berkeley point out the particular strain of bacterium in Italy’s olive trees matches a strain found previously in Costa Rica and scientific tracking of genetic data indicate it found its way via infected ornamental coffee plants.

What troubles me most is the larger picture: it’s the creeping realization the immune system itself of trees is weakening, as it is of bees, of wolves, of fish, and … the list goes on. Scientists consistently point out that temperature directly affects everything on Earth. Insects, for instance, that transmit bacteria and infection, are finding Earth’s temperature rising. Warmer weather, warmer winters, just those two variables alone encourage insect migration into geographic regions that used to be too cold for them to endure. Warmer weather affects insect developmental rates, their reproduction, and mortality. They proliferate.

In the United States alone, farmers spend more than $11 billion a year fighting weeds and pests. Yet these weeds and pests are ever expanding into areas where they haven’t been before because the Earth’s temperature is working against us. Everything is connected. Every tree, bee, wolf, or fish that dies should call out to us the words of the poet Rainer Maria Rilke: “You must change your life.”

Ursula Carlson, Ph.D., is professor emerita at Western Nevada College.