Potatoes at morning.

Potatoes at noon.

And if I were to rise at midnight potatoes I’d get. —19th-century children’s chant

In 1845, a disaster struck Ireland. A mysterious blight attacked the potato crops, destroying the only real food of Ireland’s rural population. Over the next five years, the blight attacked again and again. These years are known today as the Great Irish Famine.  

Most famine victims were Irish Catholics, who comprised 80% of Ireland’s population. Most lived in great poverty and spoke only Irish.  

Late blight epidemics also occurred in Belgium, Holland, Germany, Switzerland, France, Italy, England and Scotland. For the people in Ireland, who subsisted on the potato as a main food source, the late blight epidemics were devastating.   

In a five-year period, the population decreased dramatically as over 1.5 million people died from starvation and disease and an equal number emigrated from Ireland to the United States, Canada or Britain.

In 1845, most of Ireland’s rural population of around eight million depended on potatoes as their staple food. (Ireland was one of the most densely populated countries in Europe.)  Ireland also had plenty of poor people: about three million farm laborers lived in great poverty. Travelers were appalled at the laborers’ wretched housing, the poorly clad men and women, and the huge numbers of barefoot, nearly naked children.

From August until May, millions of  poor  men, women, and children ate potatoes for breakfast, lunch, and supper, an average of 7 to 15 pounds per person each day.  They ate potatoes boiled, roasted and mashed with buttermilk and onions. They ate potato cakes, potato bread and potato soup. Even the pigs, cows and chickens ate potatoes.


While it would appear impossible for the Irish to rely on potatoes as the sole source of food,  that may not be the case. Potatoes with the skin, are actually most nutritious.  One medium baked Russet potato with the skin has 129 calories, 4.6 grams of protein, no fat and 37 grams of carbohydrate with about 4 grams as fiber.  

The vegetable  is also loaded with nutrients, including over 30% of the daily value for immune-supporting Vitamin C. Plus, it has nearly a third of the daily target for potassium, a mineral that supports nerve, muscle, and heart function, as well as healthy blood pressure. Potatoes also provide B vitamins, vitamin K, iron, magnesium, zinc, copper and manganese. Spuds are also rich in antioxidants, including  phenols, carotenoids, flavonoids and anthocyanin compounds, which are found in both the skin and flesh of the potato.

Late Blight

Epidemics of potato late blight occurred before the germ theory had been clearly elucidated. Some believed weather was responsible. The weather in Ireland  has always been fickle, but the weather during the summer of 1845 was worse than the oldest people could remember.

First the July days burned hot, much hotter than usual. After several days, the hot spell ended and the weather turned gloomy, cold and damp. For three weeks in August, heavy rains fell every day.   

Others blamed the devil or bad soil. The painstaking work of J. Teschemacher in the United States, M.J.Berkeley in Great Britain, Montagne in France and later DeBary in Germany, clearly found that a fungus like organism was responsible for the disease. Late blight epidemics appeared in Europe before Louis Pasteur’s pioneering work on the germ theory of disease. These early researchers laid the groundwork for the discipline of plant pathology.

The Organism

The famine was caused by a plant pathogen, Phytophthora infectans, and the disease late blight is considered a reemerging problem and still causes major epidemics on both potato and tomato plants world wide.  

This is the same organism  that has most greatly impacted humanity to date.  It is best known for its causal involvement in the Irish potato famine after introduction of the HERB-1 strain to Ireland from the Americas in the 19th century.

P. infectans causes a destructive foliar (pertaining to leaves)  blight and also infects potato tubers under cool, moist conditions and can be transported long distances in infected plant materials.  To this day, potato late blight remains a major threat to food security and carries a global cost conservatively estimated at more than $6 billion per year.


Phytophthora infestans is an oomycete or water mold, a fungus-like microorganism that causes the serious potato and tomato disease known as late blight or potato blight.  

Scientific name: Phytophthora infestans

Order: Peronosporales

Family: Peronosporaceae

Phylum: Oomycota    

 Final Thoughts

P. infestans continues to cause disease on modern potato and tomato plants worldwide. More about the infestation and its affect on Ireland can be obtained in Susan Campbell Bartoletti’s fascinating book “Black Potatoes: The Story of the Great Irish Famine 1845-1850.”

Max Sherman is a medical writer and pharmacist retired from the medical device industry.  His new book “Science Snippets” is available from Amazon and other book sellers. It contains a number of previously published columns.  He can be reached by email at  maxsherman339@gmail.com.