Fusarium oxysporum. I know, you didn’t think I’d hit you with Latin right out of the gate. No, that isn’t a spell from Harry Potter (though it should be). It’s a fungus species. More precisely, according to Wikipedia at least, it’s a genetically heterogeneous polytypic morphospecies. But since I don’t know what that means and don’t really want to find out, we will just go with a fungus species. Strains of this fungus are found in soils all over the world. They are often endophytes, meaning that they grow and live within plants. Typically, these fungi will latch onto the root structures of a plant. Sometimes that’s a helpful thing, as they have been found to offer disease protection to their plant hosts. For some strains though, these fungi are a little less helpful. Take, for instance, fusarium oxysporum f.sp. cubense.
The Cautionary Tale of Banana Farming, Panama Disease, and the Inherent Risks of Monocultures
By: John A. Lanier
For decades, banana farmers have tried to stay one step ahead of a fungus that is deadly to their crops. As that task becomes more difficult, farms will face the growing risk of the complete loss of their trees. This risk is one of the reasons that monoculture farming may not be the best way to go.
This is the fungus responsible for Panama disease. Some of you may be familiar with this, but I’m guessing that this will be news for a lot of you. Panama disease is a threat to the continued viability of one of the most popular agricultural products around the world - the humble banana.
Most every banana that you find in an American or European grocery store is a Cavendish. It’s a cultivar of banana, similar to how you can have Honeycrisp or Pink Lady apples. According to the United Nations’ Food and Agriculture Organization, about 50 billion tons of Cavendish bananas are produced every year, accounting for 47% of global banana production. For decades now, it’s been the incumbent banana crop in the Western Hemisphere.
That wasn’t always the case, however. Its predecessor was the Gros Michel cultivar, which was commonly farmed throughout Central America. In the 1950s, banana farmers noticed that the leaves of some trees would wilt by turning yellow, then brown, and then falling off. Within a few years, these trees would die. Scientists determined that it was this fungus that was invading the root structures of the trees, and the fungus was spreading like wildfire. There was no effective treatment for the disease. The best a farmer could do was to dig up and dispose of the infected trees, and then hope the fungus didn’t spread any further. All it would take, however, is a bit of dirt stuck to a boot or an animal’s paw to move the disease to other susceptible trees.
Fortunately, Cavendish bananas were naturally resistant to the fungus. In the late 1950s and 1960s, banana farmers switched to these cultivars, since they produced fruit with similar flavor and characteristics to the Gros Michel. This cultivar saved the day - saved the industry, really - and all seemed to be well. But then, in the 1990s, scientists detected a new strain of fusarium oxysporum f.sp. cubense in Taiwan. This strain had evolved around the Cavendish’s natural resistance, presenting a new threat to banana farmers. Once again, all they could do was hope that the fungus wouldn’t find its way to their doorstep. For a couple of decades, the disease stayed away from Central and South American banana farms. Then, in the summer of 2019, disaster struck. The fungus was found on several banana farms near Bogotá, Colombia. In the spring of 2021, it was then found in Peru. Countries throughout the Americas are on high alert, especially Ecuador, which exports about one third of the global banana crop.
So far, the next domino has yet to fall. As a result, we can still find our favorite yellow fruits commonly available in our neighborhood grocery stores. That said, it’s likely a matter of when, not if, the disease spreads broadly throughout this hemisphere. When that happens, the prices of Cavendish bananas will rise, many farmers will lose their livelihoods, and food security will be threatened in many impoverished communities. At that point, I expect we will see different cultivars of bananas in stores, which will look and taste a bit different. If I had to bet, at some point in my lifetime I will no longer be able to enjoy the type of banana I’ve eaten for my entire life.
While scary and tragic, I haven’t really made an environmental point yet. Here it is - I think fusarium oxysporum f.sp. cubense is a cautionary tale for the monoculture form of agriculture that is so pervasive today. If you aren’t sure what a monoculture is, think of an Iowa farm with corn fields as far as the eye can see. Monocultures are when farmers plant one crop, and only one crop, in a field. The alternative is called polyculture farming, wherein several different crop species are planted in the same field.
There are plenty of reasons why monoculture farming is so common. In general though, it all boils down to monocultures being easier and more profitable than polycultures. When you only have one crop to worry about, you are able to treat every square inch of a field exactly the same, and you can plant the crops that are most valuable for that particular climate and soil type. That results in generally higher efficiency, higher yields, and higher profits.
The problem is that these benefits come with multiple costs. On monoculture farms, pests that would feed on the crop can have a field day (pun intended). That forces farmers to use many more chemical pesticides. Further, monocultures tend to degrade soil health over time. Whereas polycultures can cycle nutrients effectively, with some species restoring to the soil the nutrients that other species need, monocultures break this cycle. That forces farmers to apply lots of fertilizers and use more water, since the lack of topsoil means less water can be retained.
Then there is the economic risk that comes with monoculture farming, which brings us back to that pesky fungus I’ve been talking about. If a banana farm succumbs to the Panama disease, it can be wiped out entirely. This is true of any monoculture farm that faces a pest or disease for which there is no effective defense. Monoculture farms are the epitome of putting all of your eggs in one basket. And even if there is an effective defense, the very existence of monoculture farming can cause that defense to weaken over time. For instance, when farms broadly apply pesticides and herbicides, they are creating an evolutionary pressure on the targeted pests and weeds to evolve defenses to those chemicals. Much like the overprescription of antibiotics can result in bacteria that are resistant to medication, so too can monocultures breed more dangerous pests and weeds.
I’ll conclude with what Will Harris of White Oak Pastures likes to say about the issue. “Nature abhors a monoculture.” They simply don’t exist in the natural world, and for good reason. If we want a more resilient, adaptable global food system, then I’d say polyculture farming is the better way to go.