University of Georgia
They've changed how and where people live. They influence law and how people are governed. And as freer global trade forces the world into closer contact, plant diseases will continue to play a major role, says a University of Georgia expert.
By knowing a little history and how these diseases shape society now, we can prevent them from misshaping our future, says Ron Walcott, a plant pathologist with the UGA College of Agricultural and Environmental Sciences.
"Plant diseases in some way have affected virtually everyone in the world," said Walcott, who teaches a UGA course in Athens, Ga., on the relationship between plant diseases and society.
Sparks lawFor example, he said, a nasty, unnoticed Asian pathogen caused a disease that virtually wiped out the American chestnut tree around the turn of the 20th century. The pathogen found its way into the country through normal trade.
Until then, American chestnut trees were common nut-bearing trees all over the United States. They haven't recovered. "Chestnut blight is still here," Walcott said.
As a result of the disease, though, the Plant Protection and Quarantine Act of 1912 was enacted.
Sparks migrationsPlant diseases have contributed to massive human migrations. And some say they've played a major role in regulating human populations, Walcott said.
The most classic case of these mass migrations, he said, can be attributed to a potato disease that ravaged Ireland in 1845. At that time, the potato was the dominant food source for an Irish population that was growing out of control.
Because so much could be grown on few acres, the average Irish man ate about 12 pounds of potatoes each day. "They also produced corn, pigs and other agriculture products," he said. "But these products were used to pay the rent on the land and exported. Potato was by far the major food source."
A growing population that depends on one type of food spells trouble. Ideal weather conditions allowed a fungus to wipe out the Irish potato crop, causing an immediate famine and exodus. (Many of those Irish immigrants landed in Georgia.)
But it wasn't just the famine that caused the great Irish exodus. Due to superstition and an ignorance of plant diseases at the time, Walcott said, many thought they could do nothing else but leave.
A plant disease caused a less known, but some say much worse, famine and exodus in India during World War II, he said.
India wanted independence from Britain at the time. Tensions were high. Then Japan, Britain's war enemy, began to advance on the region.
The main food source for the Bengal region of India was rice. But a rice disease wiped out the crop. Coupled with war tensions, the disease contributed to the death or exodus of 2 million to 4 million Indians, he said.
Sparks debate over rightsPlant diseases still affect us. One disease has sparked a debate over basic citizens' rights in Florida.
Citrus canker has badgered the Florida citrus industry since 1910. There is no cure. It was thought to be eradicated several times, only to come back stronger, most recently in 1995.
To combat the spread, the state government, by law, can remove and destroy suspect trees from private property. This has upset many, particularly around the Miami citrus-growing area.
"This disease has really brought to the fore, constitutionally, what right the government has to take over personal property for the greater good of the society," he said.
Walcott's research focuses mainly on the understanding, causes and prevention of seed-borne diseases. He centers on a watermelon disease that has upset relations and caused lawsuits between seed companies and growers in South Carolina, Florida and Georgia.
The most efficient way diseases can travel is through seed. Georgia farmers get much of their seed for crops from out-of- state.