I found this interesting article I found on Farmer almanac...
Outbreak of Fungus Threatens Tomato Crop
Published: July 17, 2009
A highly contagious fungus that destroys tomato plants has quickly spread to nearly every state in the Northeast and the mid-Atlantic, and the weather over the next week may determine whether the outbreak abates or whether tomato crops are ruined, according to federal and state agriculture officials.
Green tomatoes affected by the spores of highly contagious fungus, called late blight.
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The spores of the fungus, called late blight, are often present in the soil, and small outbreaks are not uncommon in August and September. But the cool, wet weather in June and the aggressively infectious nature of the pathogen have combined to produce what Martin A. Draper, a senior plant pathologist at the United States Department of Agriculture, described as an “explosive” rate of infection.
William Fry, a professor of plant pathology at Cornell, said, “I’ve never seen this on such a wide scale.”
A strain of the fungus was responsible for the Irish potato famine of the mid-19th century. The current outbreak is believed to have spread from plants in garden stores to backyard gardens and commercial fields. If it continues, there could be widespread destruction of tomato crops, especially organic ones, and higher prices at the market.
“Locally grown tomatoes normally get $15 to $20 a box” at wholesale, said John Mishanec, a pest management specialist at Cornell who has been visiting farms and organizing emergency growers’ meetings across upstate New York. “Some growers are talking about $40 boxes already.” Tomatoes on almost every farm in New York’s fertile “Black Dirt” region in the lower Hudson Valley, he said, have been affected.
Professor Fry, who is genetically tracking the blight, said the outbreak spread in part from the hundreds of thousands of tomato plants bought by home gardeners at Wal-Mart, Lowe’s, Home Depot and Kmart stores starting in April. The wholesale gardening company Bonnie Plants, based in Alabama, had supplied most of the seedlings and recalled all remaining plants starting on June 26. Dennis Thomas, Bonnie Plants’ general manager, said five of the recalled plants showed signs of late blight.
“This pathogen did not come from our plants,” Mr. Thomas said on Wednesday. “This is something that has been around forever.”
Mr. Draper said the diseased seedlings, found in stores as far west as Ohio, were at least one source of the illness, but, he added, “It’s possible that we are looking at multiple epidemics.”
Mr. Mishanec said agricultural pathogens can easily spread when plants are distributed regionally and sold by big-box retailers.
“Farms are inspected, greenhouses are inspected,” he said, “but garden centers aren’t, and the people who work there aren’t trained to spot disease.”
Authorities recommend that home gardeners inspect their tomato plants for late blight signs, which include white, powdery spores; large olive green or brown spots on leaves; and brown or open lesions on the stems. Gardeners who find an affected plant should pull it, seal it in a plastic bag and throw it away, not compost it. Unaffected plants in home gardens and commercial fields should be sprayed with fungicide to prevent the spread of the disease. (More information can be found at a Cornell Web site, http://vegetablemdonline.ppath.cornell.edu
In Rhode Island, some farmers have plowed tomato fields under at the first sign of blight, said Kristen Castrataro, an extension agent with the University of Rhode Island.
At the Stone Barns Center for Food and Agriculture in Pocantico Hills, N.Y., half the year’s tomato crop was infected and has been lost, said Dan Barber, the center’s chef and creative director.
Tim Stark, a Pennsylvania farmer who specializes in tomatoes, said he spotted three affected plants — he has more than 25,000 in the ground — last week and was worried enough to spray them with synthetic fungicide for the first time in 14 years of farming. For good measure, he pulled all of his potatoes out of the field.
There are two strains of late blight — tomato and potato — but the illness can jump from one species to the other. It is highly contagious: A single open lesion on a plant can produce hundreds of thousands of infectious spores.
Fungicides can protect unaffected plants from disease, but there is no cure for late blight. Organic farmers, who are not permitted to use powerful synthetic fungicides like chlorothalonil, have very few weapons against this aggressive pathogen.
On Thursday morning, Chris Walbrecht, co-owner of the organic farm Garden of Eve in Riverhead, N.Y., on Long Island, found the first signs of late blight on a row of 800 Early Girl tomato plants; he said he might have to destroy them all, a major blow to the farm’s finances.
An acre of tomato plants can produce 30,000 to 40,000 pounds of tomatoes. “At $7 a pound, tomatoes are one of our most profitable crops,” he said.
Hot, sunny weather, which can kill late blight, could dramatically slow or eliminate the fungus’s spread over the next week, experts said.
“I see a day like today that’s overcast and windy, those spores are flying around everywhere, and rain tonight will bring it all down to the ground,” Meg McGrath, a vegetable pathologist on the faculty of the Cornell horticulture research center in Riverhead, said on Thursday. “The disease loves these conditions.”
This article has been revised to reflect the following correction:
Correction: July 22, 2009