Above potato image from a photo by:
Rebecca Nelson, International Potato Center

Pity the poor tubers! These potatoes infected with late blight display white, slimy lesions on their skins.
Copyright and Courtesy Ohioline

The British government responded fairly well to the starvation at first, but ultimately failed to prevent the deaths of at least 1 million Irish during a famine that lasted until about 1850.

Salvaging tubers left behind by pickers, gleaners are generally the poorest of the poor. Illustrated London News

Farmers were evicted in large numbers, the farming system broke apart and emigration became a way of life, helping the Irish become a key ethnic group in the United States. Late blight and the famine also left a residue of bitterness that persists today.

Now, with the globe much more crowded, potato experts report that the same disease, properly called Phytophthora infestans, has returned with a vengeance. (Taxonomic trivia: Although the pathogen is often called a fungus, it's more closely related to kelp and other brown algae).

Late blight, by any name, is a contender.

Unhealthy triangle
In the West, those of us who don't farm tend to ignore little pests, especially hard-to-pronounce plant diseases, assuming that somebody will always find a spray or another way to control them. Fungicides, unfortunately, are of little help against the modern strains of late blight, which few potatoes resist.

In other words, this is one of those times when even untutored acolytes of French fries must get close and personal with plant doctors. Properly called plant pathologists, these folks see crop diseases as a kind of triangulation among plants, pathogens and people.

By the mid 1840s, the Irish were growing huge amounts of potatoes. Laboring men, says historian James Donnelly, Jr., typically ate 12 (twelve!) pounds per day. He adds that according to one calculation, "out of a population of 8.5 million on the eve of the famine, about 3.3 million would have been entirely dependent on potatoes for food, and 4.7 million at least heavily dependent."

Potatoes were the most productive staple starch for Ireland's cool, damp climate, but the island also grew barley, oats and wheat. In fact, Donnelly notes, before the famine, these cereals provided a large proportion of Great Britain's grain supply -- and their export during early stages of the famine enraged the starving Irish. Although many potato varieties were grown in Ireland -- as a kind of insurance against crop diseases -- virtually all were susceptible to Phytophthora infestans, a virulent pathogen whose Greek name means "plant destroyer" and which turns plants into a black, dead mush.

As is even more true today, transportation played a key role in the crop disease. William Fry, a plant pathologist at Cornell University, says Phytophthora infestans originated and remained in Mexico's central highlands until the mid-19th century. Through an unknown mechanism, it probably reached United States in the early 1840s.

The blight presumably jumped the Atlantic aboard ship in 1845, and rapidly infested European fields. In damp conditions, Fry says, a single infected potato would be enough to spread the deadly disease. In 1845, late blight obliterated one-quarter to one-third of the Irish potato crop.

That was the prologue. In 1846, "It's not too much to say the crop was a total disaster," says Donnelly, a professor of history at the University of Wisconsin-Madison.

The introduction to Ireland of potatoes, which originated in the Andes, allowed the population to soar. Between 1750 and 1845, the Irish population "mushroomed from about 2.6 million to 8.5 million, or by some 325 percent," writes Donnelly in a new book on the famine (see "The Great..." in the bibliography).

Donnelly admits the diet may have been "stodgy and monotonous," but says buttermilk and fish filled out the protein. British Army records show that Irish men were relatively healthy, indicating that the boring diet was also fairly nutritious.

Socially speaking
Like all diseases, the social and political context contributed to the blight. The deaths were not due just to disease, but also to overpopulation, extreme fragmentation of holdings, enormous income inequalities between rich and poor, and British hostility to Ireland. The initial response of the British government -- removing a ban on grain imports and creating make-work jobs for destitute farmers and laborers -- was helpful, but London soon washed its hands of its Irish woes, with deadly effect. "If from the fall of 1847 the government had taken a more interventionist role with respect to distributing food among the classes that were in misery," Donnelly says, "it had the capacity to save several hundred thousand lives."

Between 1848 and 1850, he adds, when the Irish "were still dying in large numbers, the problem was not the absence of food, but the fact that it wasn't being distributed to those in greatest need." In a pattern that persists today, the problem was not simply a plant disease, Donnelly insists. "Ultimately, people died because they were so impoverished and because of appalling government failures."

What is late blight, and why is it back in the news?