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 law

For 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 migrations

Plant 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 rights

Plant 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.