PlatanoColombia/WikimediaCommons
No, not that banana disease.

Environment Issues

You may have heard that virtually all bananas we eat are from the genetically identical Cavendish cultivar. You’ve also likely heard about a big, scary disease called Fusarium Wilt (also known as Panama Disease) that evolved to threaten the previously resistant Cavendish. (Panama Disease basically knocked out the last great banana cultivar, the Gros Michel—French for “Big Mike!”)

But there’s another, less dramatic disease that actually causes larger global yield losses than Fusarium Wilt. It’s called Black Sigatoka or Black Leaf Streak disease, and climate change has increased its risk by 44 percent since the 1970s, according to a new study by researchers at the University of Exeter.

Unlike Fusarium Wilt, Black Sigatoka does not kill off entire banana farms. Rather, it affects the plant’s leaves, which can in turn interrupt the fruit ripening process and depress yield by up to 80 percent, according to the study.

Unlike Fusarium Wilt, Black Sigatoka does not kill off entire banana farms. Rather, it affects the plant’s leaves, which can in turn interrupt the fruit ripening process and depress yield by up to 80 percent, according to the study.Scot Nelson

Photo of a tree in Hawaii affected by Black Sigatoka

The fungus that causes Black Sigatoka thrives on wet leaves and in temperatures that hover around 80 degrees Fahrenheit. The researchers found that climate change has bred precisely these conditions in many banana-growing regions in Latin America. They came to these conclusions by cross-referencing experimental data on Black Sigatoka infections with 60 years of climate data. “I was surprised by the strong climate change signal in the data, for Latin America,” researcher Dan Bebber wrote in an email. “Conditions have definitely improved for the fungus across large areas.”

“Black Sigatoka is definitely a forgotten disease, but it costs banana growers hundreds of millions of dollars to control.”

Black Sigatoka can be controlled by fungicides, but Bebber says it develops resistance very quickly. Farmers have to spray many times over the course of a growing season, switching chemical formulations often. It’s expensive and increasingly environmentally unsound. “For sci-fi fans, it’s like fighting the Borg,” he adds. (I had to look it up—it’s a group of cyborgs in Star Trek that adapts to changing conditions with great agility. Checks out.)

Since it was first identified in Honduras, Black Sigatoka has spread to Latin America, the Caribbean, and even parts of Florida. And while the study acknowledges that humans certainly had a hand in spreading the fungus via trade routes, climate change has clearly aided in its spread and survival. Though the study does not make any predictions about the future of the fungus, it stands to reason that rapidly-evolving fungicide resistance coupled with a changing climate may mean it won’t go away on its own.

“Black Sigatoka is definitely a forgotten disease [but] it costs banana growers hundreds of millions of dollars to control … we urgently need more research to develop sustainable, affordable solutions,” Bebber says.

H. Claire Brown

Claire Brown is a staff writer for The New Food Economy focusing on food policy and the environment. Her reporting has won awards from the Newswomen’s Club of New York and the New York Press Club. She is based in Brooklyn. She can be reached via email at [email protected] or on Twitter at @hclaire_brown.

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