Outbreaks of potato blight in the 1840s caused a famine in Ireland that cost the lives of over one million people and caused another million to migrate. But the disease has not gone away.
Now scientists say they have worked out the genetic sequence of the microbe that causes blight - and are closer to knowing how to fight it. Their work is published in the Journal Nature.
The BBC reports water mould Phytophthora infestans still destroys crops worldwide worth $US6 billion each year. In 2003 it wiped out the entire crop of Papua New Guinea.
Scientists hope the genome will help in developing new defences to the blight.
The mould thrives in cool, wet weather and can infect potatoes and tomatoes, causing a "late blight" that can destroy entire fields in just a few days.
However, the BBC reports the problem appears to be getting worse as the organism continues to evolve.
Potato farmers have to spray chemicals each week to keep the mould at bay, but even then it can come back.
In recent years, growers in Britain have been forced to increase chemical spraying by up to 30%.
In Ireland, farmers have described this season as the worst in living memory.