The Irish Potato Famine killed at least a million people and drove a million more out to other lands like America. For a humanitarian disaster of such massive scale, its root was in the tiny details of agricultural know-how.

The dangers of monocultures in farming are a lesson still yet to be learned in some parts of the world, explains Jean E. McLain in an editorial published by the Soil Science Society of America.

“In the 150 years since the Irish Potato Famine, hunger has continued to wreak havoc in the world… Ten million people are reported to die each year from hunger-related causes,” writes the research scientist and biologist. “Threats arise from multiple causes, including climate change and poor seed stock, but are exacerbated by monoculture.”

By the 19th century, the poor farmers of the Emerald Isle had come to rely heavily on a single variety of potato called the Irish Lumper, that was fully nutritious. According to McLain, a single acre of potatoes planted in the cool and moist Irish soil could produce 12 tons of the tubers each year. That harvest could feed a family of six comfortably, and without significant malnutrition.

Furthermore, by storing a single seed, and tending to a single crop, it got rid of the agricultural guesswork. One potato – a monoculture – meant more efficient farming, and greater yields.

But the monoculture’s success bred a problem. By creating the monoculture of the single potato among thousands of acres, it made all the fields susceptible to blight.

The blight came in the fall of 1845. The fungus was identified as Phytophthora infesans, and specifically the HERB-1 strain, McLain said. Leaves on the plants first blackened and curled – and then the potatoes that were dug out of the ground shriveled and rotted quickly, making them inedible.

Since all the potatoes were the same variety, the fungus spread quickly. A single plant had the capacity to infect thousands of other plants in a matter of several days.

“Large homogenous crops enable bacteria, viruses, fungi, and insects to specialize on one specific host,” writes McLaint. “This kills the entire crop and increases the chance that these microbes could mutate into an even more harmful variety.”

Eventually, after the disaster had abated in Ireland, science cultivated potatoes that were resistant to HERB-1 strain of the fungus, which is now believed to be extinct, McLain said.

Monoculture continues to hold sway in some parts of the poorest parts of the developing world. And crops continue to be wiped out, causing damage to people and economies. One of the most recent examples is the ongoing destruction of the Cavendish banana by a virulent fungal strain known as TR4. A Dutch team has said they have genetically engineered certain strains with resistance to the fungus – but the fruit has yet to be deployed widely across the globe.

McLain says in her editorial that increasing crop diversity, crop rotation, and intercropping – by planting rows of different crops between the main crop to hold off spread of disease – could be a way to prevent another disaster the scale of the 19th century Irish disaster.

“This argues for diversity in the world’s crops to reduce hunger and starvation, even if this entails lower yields,” she writes.

Irish peasants starving during the Potato Famine, 1846.