Potato Blight Has Come Back With a Vengeance

Nearly 150 years after a potato fungus brought famine to Ireland, scientists and growers are running up against potent new forms of the disease.

The potato late blight was once easily controlled. The fungicide metalaxyl made fast work of Phytophthora infestans whenever it struck.

But more aggressive and resistant forms of the blight began showing up in the United States and Canada in 1990, after plaguing European farmers in the 1980s.

From Maine down to Florida and across to Washington, growers have had to revert to old pesticides that must be sprayed earlier and more often to keep the blight spores off plants in the first place.

Cool, wet weather that favors blight let a resistant form take hold in Maine last year, causing as much as $25 million in damage. Washington state and Florida also have reported serious crop damage since 1990 from the new strains.

Resistant types have been identified in at least nine states and may be present in at least four others. New types have been found in Canada, Egypt, Israel, Japan, Korea, Russia and South America.

Scientists predict a long, expensive struggle.

“The disease is going to be more difficult to control than it used to be,” said William E. Fry, plant pathologist at Cornell University. “How much more, we’re going to have to wait and see.”

The new types are emerging just as governments want to wean agriculture from its environmentally damaging chemical dependency. Farmers don’t like the extra cost either.

Galen Flewelling, a grower in Easton, Me., expects he’ll be spending $30 an acre more to treat each of his 450 acres this season.

“We’ll be spraying as soon as the plants come through the ground, rather than waiting until they are six or seven inches high,” he said.

But there’s little choice. The fungus can burn out a field over a weekend. “It’s like somebody took a flamethrower to it,” Fry said.

One blighted potato, brownish purple with a dark, corky rot, can ruin all the others stored with it.

In poorer parts of the world, the costs could hinder efforts to grow more potatoes, an increasingly important staple in countries like Bangladesh, India and China.

Scientists say the best hope is to develop new, resistant potatoes. Such work is under way in Peru--which has been unaffected--the United States and elsewhere.

The same fungus wiped out the Irish potato crop starting in 1845, causing 750,000 people to die from illness and starvation and leading to massive emigration to the United States.

The fungus never vanished. But only one of two “mating types,” A1, was involved, and scientists controlled it.

But around the 1970s, another variant known as A2 made its way to Europe from Mexico, where the blight started.

The A2s turned up in 1990 near Vancouver in British Columbia and in Athens, Pa., 10 miles from the New York border. No one knows for sure how they got there.

In addition to Maine, Florida and Pennsylvania, A2 fungi have appeared in California, Michigan, New York, North Carolina, Tennessee and Texas; and the Agriculture Department says Minnesota, Oregon, Washington and Wisconsin “very likely” have the A2 fungus as well.

Spores of the fungi have to be attached to the potato to survive, which is one reason Maine is getting nearly $3 million in federal money to dispose of discarded potatoes and inspect seed potatoes that could spread the fungus.

When A1s and A2s mate in infected plant tissue, they produce a hardy “oospore” that can survive in the soil, crop debris or even crates from one year to the next.

The breeding leaves open the possibility of new, more virulent types developing. It’s possible some mating has occurred in the Pacific Northwest and in Manatee County, Fla., said Fry.

“We will see the result of that in the next several years,” he said.