First reliable maps track spread from US of potato blight that caused Irish famine in mid-19th century

Study by scientists at North Carolina State University predicted to help track spread of modern pandemics

The first accurate maps detailing how an outbreak of potato blight hit North America before crossing the Atlantic and causing the Irish famine between 1845 and 1852 have been compiled by scientists in the US.

What was then a mystery disease arose in the US between 1843 and 1845 before spreading to Europe. In 1845, first reports of the disease arose in Ireland and Scotland. It caused mass starvation and the deaths of about 1 million Irish people. The famine also prompted emigration in the opposite direction, with more than 1.5 million people leaving Ireland for the US during the period from 1845 to 1855.

“Since the fungus-like plant pathogen was unknown to science at the time, the cause and source of the disease as well as remedies for control were widely discussed in agricultural reports, newspapers, and government pamphlets,” researchers at North Carolina State University note in a study published in Scientific Reports on Thursday.

“We have created the first accurate maps of the 1843–1845 outbreaks of potato late blight in the US. Our text analytics has also revealed information on theories of the cause and methods of control.”


The findings track the flight of the disease caused by a fungus-like pathogen known as Phytophthora infestans. The researchers believe they could also help to improve tracking of modern day pandemics.

A team led by Prof Jean Ristaino concluded that the disease was first reported in 1843 at five locations in the states of New York, Pennsylvania, New Jersey, Delaware and Connecticut. By end of 1844 it had spread to a further six states (Ohio, Massachusetts, Rhode Island, Vermont, New Hampshire and Maine) and the Canadian province of Nova Scotia. In 1845 it spread to Michigan, Illinois, Indiana, Maryland and the Canadian province of New Brunswick.

Reports from the time suggest it led to crop losses of between 33 and 50 per cent.

The authors compiled historical theories on the source of potato blight and suggested remedies for treating it. Proposed causes included insects, weather conditions, poor quality potato varieties and a fungus. They focused on widely described debates about whether the fungus caused or was a consequence of the disease.

Suggested treatments included calcium oxide (lime), sulphur, copper sulphate (bluestone copper) and salt. Infected imported potato seed tubers from Nova Scotia, France and Bogotá in Colombia were suspected as sources of the disease.

The scientists used text analytics on historic and modern writing to reveal more information about the effects and spread of the plant pathogen that continues to vex growers of potatoes and tomatoes. They examined keyword terms such as “potato rot” and “potato disease” after digitising historic farm reports, news accounts and US Patent Office agricultural records to reveal how the pathogen spread.

They also used text analysis tools to track social media feeds for the modern-day spread of late blight. “This analysis holds promise as a useful tool to help researchers track and visualise both historic and current plant diseases,” Prof Ristaino said.

“We searched those descriptions by keywords, and by doing that we were able to recreate the original outbreak maps using location co-ordinates mentioned in the documents. We were also trying to learn what people were thinking about the disease at the time and where it came from,” she said.

In addition, they examined tweets from 2012 to 2022 to learn more about modern spread of the disease, mining tweets for both common and scientific names of the pathogen – and geolocated sources.

“The social media mining was interesting because we found that most people talking about this disease are scientists in developed countries promoting their own work on Twitter (now X),” Prof Ristaino said. “It was also interesting to note that states where the disease appeared all those many years ago still have the disease now.”

These tools, she said, “will help researchers explore and map unstructured text to track and visualise pandemics”.

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Kevin O'Sullivan

Kevin O'Sullivan

Kevin O'Sullivan is Environment and Science Editor and former editor of The Irish Times