🎓 On Agricultural Causes of Societal Catastrophes

A look at maize mosaic disease, wheat rust, the chestnut blight, brown spot disease, and the boll weevil.

After my article about potatoes in the context of colonizing Mars, a reader reached out remarking on the potato blight, which sent his ancestors (and some of mine!) fleeing Ireland to make their fortunes. He wondered how common it was for plant diseases to cause that sort of societal collapse — as opposed to something like Panama Disease, which was a bummer, but the loss of “the delicious banana” certainly didn’t cause widespread famine or anything.

Maya

The best example I found of societal collapse caused by plant disease is how Mayan civilization (probably at least partially) collapsed because of maize mosaic disease¹, which thrives in the year-round maize cultivation possible in tropical environments like the Yucatan rainforests. It’s spread by planthoppers (like grasshoppers but significantly weirder looking, and stunts plant growth.

There’s Paleoclimatic data indicating that severe droughts also contributed to the famine and societal breakdown. Of course there’s also “war,” which tends to be one of those things where you don’t know if the increased rate of war caused or was caused by problems getting enough food. But as with Ireland’s potato famine, I would bet that maize mosaic disease is a plausible contender for “really made things a lot worse” and “blights are really bad.” It’s hard to be precisely sure, though, because the thing about a nasty civilizational collapse is that the records tend to be pretty spotty.

Rome

Rome at least had the grace to exist contemporaneously with other nearby civilizations that didn’t collapse, and to live in an environment that lends itself pretty well to leaving archaeological evidence. The rainforest is not so great for preserving codices, if any existed.

I don’t think Roman collapse had much to do with monoculture, though they certainly relied on grain. Wheat rust was such a big deal in Ancient Rome that there was entire god(dess?) devoted to it. Robigus was admittedly a relatively minor and obscure god in Ancient Rome, but even so there was a festival (April 25!) — one of the darker (and more desperate) of the Roman harvest festivals. Apparently², they sacrificed a dog to try to keep the wheat crop healthy.

The wheat crop was critically important to Rome, and wheat rust was a perennial threat. It wasn’t until the 20th century that K. C. Mehta figured out wheat rust’s lifecycle. In antiquity, they just knew the devastation was cyclical and awful. It’s one of the reasons Roman authorities invested in grain imports (e.g., from Egypt and North Africa) — it was a way to hedge against local crop failures. This diversification was a proto-strategy against monoculture risk.

Based on what I know about bananas and potatoes, we are… less good about hedging these days — although we do at least have genetic engineering going for us, and most places aren’t reliant on one crop. Plus, we have fungicides. The Romans prayed, U.S. Farmers spray is a great line from the Crop Protection Research Institute. There’s also the whole “grain subsidies” debate, which I am not going to get into here.

India

A less loaded (for me, at least, not being Indian) example of modern-day hedging against crop failure is the result of the Bengal Famine of 1943, which was, yes, exacerbated by wartime hoarding and colonial mismanagement (they literally destroyed rice stockpiles for fear the Japanese might invade). But fundamentally, brown spot disease represents one of history’s deadliest plant disease disasters. The fungus infects rice leaves and grains, and thrives in precisely the kinds of unusually high temperatures and torrential rains caused by the 1942 monsoon season. It didn’t help that a nasty cyclone destroyed a ton of rice stocks and standing paddy crops, or that the cyclone’s floods also spread the fungal spores far and wide.

An absolutely massive amount of rice died.

The British Raj’s abject failure to import food in time fueled anti-colonial sentiments, strengthening India’s independence movement. I’m sure you can see the parallels to Ireland. Is it civilizational collapse to say it was a major reason the British Empire had to give up control of so many colonies? India got its independence in 1947, and honestly, by the standards of “Rome collapsed” and “the Maya collapsed” I think it is extremely fair to say “the British Empire began its collapse” here. It abandoned Palestine in 1948. Malaya went independent in 1957, and by 1967 20 British colonies were independent.

Sure, brown spot disease wasn’t the only cause — there’s never just one, and the British Empire didn’t “officially” end until the loss of Hong Kong in 1997 — but I do think it’s a big one.

One of the interesting bits is how plant pathologist S.Y. Padmanabhan proved (by meticulously compiling data) that a big reason for the famine really was nature, it wasn’t (just, appallingly) bad policy. His 1973 paper led to the development of better fungicide and more blight-resistant rice varieties. Post-independence governments prioritized food self-sufficiency (e.g., building grain stockpiles and research institutes) to avoid dependence on one crop variety.

America

You see that pretty often, actually. After the boll weevil hit the American cotton belt, crop rotation got a lot more popular. The South’s one-crop economy gradually diversified. Peanuts, livestock, and later soybeans joined cotton in rotation, which helped improve the soil too.

I’m not sure that you could say that the cotton crashed led to the collapse of the American South in the early 1920s, but it certainly caused a great deal of societal change when so many farmers migrated north.

By contrast, I’ve heard (and made) pretty solid arguments that the Chestnut blight is largely responsible for the collapse of the Appalachian economy and the decline of Appalachian culture.

Chestnut trees are a really great tree that produce excellent timber for housing and furniture. Their wood was prized for its strength and rot-resistance, much like cedar. One chestnut tree could produce over ten bushels of nuts during harvest season — a year’s supply for a family of four.

Chestnut forests are a great place to fatten up livestock like pigs and cattle, which by the way do just fine in forest environments. They’re also an important source of food for game animals like squirrels, turkey, and deer. Although deer are basically considered suburban rats where I live, they’re an indispensable source of food in rural areas.

The economic impact of chestnut blight on Appalachian families was massive. Since chestnut lumber is straight, easy to work and rot-resistant, it was used for everything from fence posts to building construction to instruments. Chestnuts themselves were a significant cash crop, not just because of the holiday season (they ripen during winter), but also for feeding livestock. Aside from that, chestnut tannins were used for the tanning industry; the southern Appalachians produced half the U.S. supply at the time.

The loss of the American chestnuts literally destroyed the self-sufficient Appalachian mountaineer way of life. Although others might argue that a specific region isn’t “society” and Appalachia is certainly still civilized by the standards of the ancient world… losing that led, in some important ways, to societal collapse.

Blights are bad, yo.

Further Reading

• Scholars have done the work of tracing the role of human civilization in the globalization of plant pathogens, so I won’t repeat the effort here, these sorts of devastating blights have happened before humans were even a consideration. Pollen analysis from the mid-Holocene suggests two massive, catastrophic declines occurred in Northern Hemisphere forests: a hemlock decline in North America and an elm decline in Europe. The article has some nice maps if you’re as into that sort of thing as I am. It also points out that although the Columbian Exchange vastly increased the spread of invasive species, plant disease outbreaks that trigged famines mass human migrations have been reported since the beginning of history.

• I’ve written about famines before; for more about how and why they happen (and to whom) check out my article about how agrarian societies experience famine.

• Jordan Yanowitz
  wrote an interesting article touching on how to define the global onset of the Anthropocene that didn’t end up being relevant to my points here. I still enjoyed reading it while putting together the research for this article, and you may too.

• I did a bunch of research into fungus back in 2021, click thru for a quick overview of what I learned about hallucinogenic urine drinkers & the fungi-cleaning duties of ancient priests.

• For more about antifungal rituals in the ancient world, check out my article about practical religion, which touches on how the ancients dealt with mold.

• To learn more about monsoons, like the one that caused the Bengali famine, check out my recent livestream review of my notes from Beyond the Blue Horizon by Brian Fagan. I try to do a 30 minute livestream notes review session every Thursday morning, to motivate myself to get on the treadmill. Join me next week — I hope to review my notes from Against the Grain by James C. Scott.

1. Scholars in the 70s speculated that maize disease caused Mayan society to collapse; from what I can tell, the current debate is a riff off of the whole “did Rome really fall?” thing. “There is now a consensus that Maya civilization as a whole did not collapse, although many zones did experience profound change.” It’s a dumb semantics argument, in my opinion. For the purposes of a discussion of “does widespread crop failure mean the civilization collapsed” my answer is “yes” for the reasons Bret Devereaux outlines here in regard to Roman decline.

2. Marcus Terentius Varro (Rome’s “third-greatest” scholar, ouch) wrote about rust prevention rituals and farm practices around the 1st century BCE. One of the interesting things about ancient scholars is that they tended to be very knowledgeable generalists; Varro had been a soldier in Pompey’s army, a successful farmer, and also an insightful author on a variety of topics including history and microbiology.