P. infestans news bulletins

Infection Threatens Idaho Spuds

APO 08/15/97 03:23

Copyright 1997 The Associated Press

POCATELLO, Idaho (AP) -- Farm experts say the light blight infection threatening southern Idaho potatoes will not destroy crops if the disease if handled properly.

But treating the infection will cost growers $100 to $160 an acre, which could wipe out profits for years.

Treatment would raise the cost of growing an acre of potatoes by up to 12 percent, said Gary Bingham, manufacturing representative for ISK Biosciences, co-sponsor of a seminar for growers. The bad news comes as growers are still reeling from last year's rock-bottom potato prices.

The fungus that caused the Irish potato famine in the 1840s swept into southeastern Idaho for the first time this July because of unseasonably cool, wet weather. It has bedeviled farmers across the world for years.

"We're going to have to manage our crops in Eastern Idaho as though we had blight in every field," said Phillip Nolte, University of Idaho seed potato specialist.

"The first year is the worst," Nolte said. "Everybody's going to be a lot more educated when it rolls into next season."

Late blight, marked by reddish-brown lesions on leaves and stems, has been confirmed in about 40 percent of fields on the Snake River plain from American Falls to Ashton.

About 5 percent of fields have been destroyed.

More storms could aggravate the problem because airborne fungus spores need moisture to thrive and spread.

"Two to three weeks of dry weather and you people will come smelling like a rose," said Neil Gudmestead, a plant pathologist at North Dakota State University.

Some farmers are still playing catch-up, he said, but a strict regimen of chemical treatments and careful storage practices can limit the damage caused by the disease.

That is cold comfort for farmers such as Dennis Aye. In two weeks, he has spent $35,000 spraying his 750 acres of crops on the Tyhee Flats.

"All the cotton-picking money we're spending is worrying," he said. "But I'm pretty sure we got it under control." Jonelle Buchta, wife of farmer Chuck Buchta, who owns 4,000 acres in American Falls and Aberdeen, said she was concerned about harvesting.

"If it gets into our cellar, that's going to turn into mush."

New Potato Blight Strikes U.S. Crops

Descendant of Irish Farmer Could be Ruined by Outbreak

The Baltimore Sun
Sunday, July 30, 1995
The New York Times News Service

"We've had freezes; we've had too much rain; we've had drought. Nothing has scared us like this." --Murray Mahany, potato grower

ARKPORT,N.Y.--A perverse sort of historical symmetry is at work in Murray Mahany's potato fields. Almost 150 years after the potato blight drove his great-great-grandfather out of Ireland, a virulent new cousin of the same disease is threatening to drive him out of the only business he has ever known.

Mr. Mahany found the potent fast-moving fungus known as late blight in one corner of his 600 acres of potatoes this summer and immediately plowed it under.

But he has no way of knowing whether he has controlled it and no way of knowing whether he will earn a dime from his $5 million investment until he harvests his crop in September.

In what scientists are calling the worst threat to America's potato crop in decades, an aggressive new strain of the blight that devastated Ireland in the 19th century is sweeping across the nation, showing remarkable resistance to all chemical fungicides.

First reported in the United States in the late 1980s it has spread up the east coast from Florida to Maine.

Last year it reached New York State where the crop was down 3 percent. This year it has reached the potato-belt states of Idaho and Oregon where heavy rains have fueled its growth.

Federal agricultural officials said they would not know until year's end how many acres have been destroyed by the disease, which cost Maine farmers more than $25 million last year and put several major growers out of the potato business.

If it wreaks similar damage on the Western states crops it could drive up the price of potato products by the fall, federal officials said.

"This is the worst crisis to have hit the United States potato industry in history," said Dr. Kenneth Deahl, a research microbiologist with the U.S. Department of Agriculture in Maryland, "and the worst internationally since the Irish blight of the 1840s." [Dr. Deahl is an African-American whose slave great-great-grandfather was forced from Ireland due to the famine-causing blight. Dr. Deahl went into the study of the fungus as a result of his interest in his slave-ancestor's tales.]

The new fungus has also been reported in major potato-growing areas across the world, and some scientists predict that it could cause famine in South America if it is not brought under control soon.

Its march across the world's potato fields has inspired the creation of a special mailbox on the Internet where scientists and growers share tips on how to fight the blight.

In New York, potatoes are the state's third largest cash crop after corn and hay, generating about $50 million a year. The fungus has been found this year in the Finger Lakes region and the southern tier counties, where Mr. Mahany lives, near Pennsylvania. Sparse rain has helped curb the spread of the fungus but high humidity is encouraging its growth.

On a recent afternoon, Mr. Mahany watched stoically as his son Gary snapped open his Swiss army knife and cut a potato plant. Its green leaves and delicate white flowers seemed perfect to the untrained eye, but nestled along the stem was the telltale fuzzy gray of the late blight fungus whose scientific name is Phytophthora infestans.

"This could take out this whole field in five days," said Mr. Mahany, the fifth generation in his family to farm potatoes in America. "My return, the boys' livelihood, everything we've made in this life could be wiped out."

Scientists believe that the new strain of blight originated in Mexico, the birthplace of the blight that ravaged Ireland, starving 1 million people and forcing 2 million others to emigrate to America.

The new strain is especially virulent because it can reproduce sexually, with cells from different plants combining to form new organisms. By allowing greater genetic variation, sexual reproduction has produced strains that spread faster, survive harsher environments, and resist more chemicals.

"When it gets going, it's like a train," said Paul Toolley, a research plant pathologist with the U.S. Department of Agriculture. "It cannot be stopped."

Scientists say the only sure way to defeat the new strains is by breeding potatoes that can resist the disease, but such breeds may not be available for several years.

That may not be soon enough to keep Mr. Mahany and others like him in the potato business. "We've had freezes, we've had too much rain, we've had drought," he said. "Nothing has scared us like this".

This is why the international Commemoration of the Potato Famine--the International Potato Abstention--is so important. The commemoration hopes to bring an awareness of the work of scientists who are trying to outrun this fungus and save farmers.

Additionally, although the article above did not mention it, the potato crop in Ireland has been badly hit now for the third year running. Dr. Deahl will be making a trip to attend a high level meeting in Ireland in September 1995 to work with others on the crisis.

Massive Migration of Potato Late Blight Fungus Poses Threat

CU Press Release (02/10/93)
Feb. 10, 1993
Contact: William Holder
Office: (607) 255-3290
Home: (607) 272-1498

ITHACA, N.Y. - Variants of the fungus that caused the Irish potato blight of the 1840s are spreading throughout the world with potentially serious repercussions for home gardeners and commercial growers.

Now well-established in Europe and Mexico, the variants have gained a foothold in the United States during the past three years. Last summer, infestations were reported at numerous new locations, ranging from New York to Washington State, according to Cornell University plant pathologists.

The ongoing migrations may be the first worldwide spread of potato late blight since the devastating migration that produced famine in Ireland, although that assertion has yet to be proved, said William Fry, Cornell professor of plant pathology.

While no one expects famine from the blight, which infects potatoes and tomatoes, scientists are concerned that the new fungus will significantly complicate efforts to control infestations, and that uncontrolled infections could diminish yields and profits for farmers. They could not estimate the potential damage from this outbreak. Some of the variants are resistant to metalaxyl, the fungicide most commonly used for control.

"This disease is remarkably explosive," Fry said. "An affected field looks like it has been burned."

The new migration contains forms known as the A2 mating type of P. infestans, which can sexually reproduce with the already well-established A1 mating type (cause of the Irish potato famine). This worries scientists, because sexual reproduction produces spores that can survive possibly for months in the soil. Such spores have been observed in Europe and Mexico, but not so far in the United States.

Steven Slack, Cornell professor of plant pathology, cited his concern that spores in the soil would lead to more blight outbreaks. Without spores, the disease must overwinter in tubers or plant material to survive.

Compounding the problem for New York growers is that the wet weather of 1992 caused some potato and tomato fields to be abandoned, and these have become ideal repositories of disease.

Representatives of Cornell Cooperative Extension and industry have formed a blight working group in New York to facilitate adoption of disease management strategies. A forthcoming publication, written by Rosemary Loria, associate professor of plant pathology, warns that the abundance of blight sources resistant to metalaxyl "does set the stage for major disease management problems." Control of the disease in Washington state over the last several years has proved to be much more difficult than growers expected.

The disease poses special risks to home gardeners and organic farmers, who typically do not adopt the chemical control measures used by commercial farmers. The Cornell researchers urged both groups to destroy any infected plants and, in areas where blight is present, to keep potato or tomato plant material out of composts, where the disease may survive through the winter.

The first signs of blight are brown flecks on leaves and stems, but the disease is most easily characterized a few days after onset by white, velvety growth at the edge of brown-black lesions.

"Commercial growers and producers of seed potatoes will have to be very careful," Slack said. Because it's impossible for farmers to keep out the disease, they will have to adopt strategies to minimize a recurrence. These include eliminating sources of disease, adopting resistant cultivars and using protective fungicides - once infected, a plant cannot be saved.

Growers are advised to inquire about the presence of late blight in potato seed fields, tomato transplant fields and even in greenhouse-grown tomato transplants. Late blight was not found in New York seed fields entered for certification in 1992.

The A2 mating type poses yet another peril. Sexual reproduction produces the most genetic diversity, and combinations of A1 and A2 could yield new and more virulent strains of the disease, according to Fry.

DNA fingerprinting

Evidence suggests that, so far, the fungus has propagated asexually. Use of DNA fingerprinting and other techniques (carried out by Stephen Goodwin, a research associate at Cornell) strongly indicates that prior to 1980, isolates of fungus from several continents (excluding North America) were all derived from a single clonal line. To what extent the variants will cross-breed is unknown, Fry said.

The central highlands of Mexico appear to be the home of the potato blight fungus. Historically, it is the only area where both mating types occur in equal frequency (the A2 type has been known since the 1950s). This also is the only location containing all the known DNA fingerprints, Fry said. The fungus is believed to migrate primarily on seed tubers (potatoes to be planted for the next year's crop). Europe is a particularly rich source of such spread, since the cool climate and low incidence of aphids make the region ideal for growing seed potatoes.

The second known migration, including the A2 mating type, probably occurred out of Mexico in the late 1970s, Fry said. The A2 mating type has been reported in all continents except Antarctica and Australia. In Europe, new populations containing the A2 type displaced the existing A1 population in only a few years. This suggests, Fry said, that the new population is more fit and perhaps more aggressive, thus explaining the heightened visibility of blight in Europe and the Middle East during the 1980s.

New Strain Of Irish Potato Famine Fungus Threatens U.S. Growers


HASTINGS---New strains of the fungus that wiped out crops 150 years ago in the Irish Potato Famine are being detected in the United States and could cause devastating losses to potato growers, a University of Florida researcher says.

Until 1990, only one strain of "late blight" was detected in North America, but in 1992, a second strain was discovered. Now researchers fear that the sexual reproduction of these two strains could produce newer, aggressive strains that may wreak havoc for potato growers across the nation, said D.P. Weingartner, with UF's Institute of Food and Agricultural Sciences.

September 1995 marks the anniversary of the Irish Potato Famine, which over a two-year period wiped out Ireland's main cash and food crop and forced thousands, including John F. Kennedy's ancestors, to emigrate to America.

"It's an ironic coincidence that the 150th anniversary of late blight in Ireland coincides with changes in the fungus, which may be second in importance only to the initial introduction of late blight into North America and Europe in the 1840s," Weingartner said.

Resistance to fungicide used to combat late blight prompted detailed studies, which led to the discovery of this new strain that spreads faster, is more difficult to control and reproduces differently, Weingartner said. Both strains of late blight have been found in Florida, destroying entire crops.

Florida growers cultivate 42,000 acres of potatoes, with more than 27,000 acres in production in the northeastern counties of Putnam, St. Johns and Flagler, Weingartner said.

To grow potatoes, growers plant "seed tubers," or potatoes cut into two-inch pieces that contain an "eye" or sprout, he said.

Presumably, seed tubers transmitted late blight, which originated in the highlands of Mexico and then made its way to Europe and finally across the Atlantic Ocean to North America.

To combat late blight, Florida growers import seed tubers from states that have inspections and are assured for the lowest levels of late blight.

"The relative impact of late blight during a given season will be dependent on weather conditions, blight severity in potato seed-producing states, mix of genotypes introduced in seed tubers and diligence of commercial growers in practicing good management practices," Weingartner said.

The coupling of the two strains of late blight will produce a resistant spore that can survive in the ground all year, Weingartner said.

Late blight, which causes visible brown lesions on potatoes, is currently controlled using a fungicide. Extensive use of fungicide coupled with generally unfavorable weather conditions for late blight development in most North American potato- producing regions reduced its spread in the late 1980s and 1990s, Weingartner said.

"Even when late blight occurred in Florida potatoes during this period, timely application of fungicide quickly eliminated the problem," Weingartner said.

New potato variety

In separate potato studies, a new variety of potato developed by Cornell researchers resists a major insect pest as well as do potatoes treated with a potent chemical insecticide, the researchers report.

Ten years in the making, the potato controls the Colorado potato beetle just as well as do potatoes treated with aldicarb, a highly effective pesticide that was withdrawn from the market, according to Robert Plaisted, a professor of plant breeding and biometry. He estimated that this new cultivar could reduce farmers' production costs by $200 an acre.

Aldicarb was withdrawn by its manufacturer two years ago because it had the potential for significant ground water pollution. Farmers have had no substitute that is as effective at controlling this pest, Plaisted said. It is a serious problem anywhere potatoes are grown, although the worst infestations have occurred in Long Island and New Jersey.

The Cornell potato has not yet been marketed, but Plaisted said he is confident that one derived from it will be available soon to growers. The variety being tested is currently available as a source of germplasm, or seed material.

News Service science writer William Holder contributed to this report.

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