Blue mold forecasting model has use in war against bioterrorism

Sitting on the banks of the Chowan River in northeastern North Carolina waiting on the fish to bite, Charles Main is wishing he could predict the movements of underwater activities as well as he does blue mold that travels through the air.

The 69-year-old, white haired and retired North Carolina State University scientist helped develop a plant disease tracking system that's getting a lot of play these days, both with farmers battling blue mold and with the war on terrorism.

The North American Plant Disease Forecasting Center (NAPDFC), which operates out of the North Carolina State University plant pathology department, tracks the movement of blue mold and other plant diseases throughout the world. It relies on reports from scientists in all the U.S. tobacco-producing states, as well as correspondents in Mexico and Canada.

On the heels of a blue mold epidemic last season in flue-cured country, Main and meteorologist Thomas Keever had already issued a blue mold warning in early March for the U.S., based on blue mold spottings in Cuba, Mexico and Texas. Last season, blue mold showed up in a greenhouse in Wake County, N.C., in mid-March.

“I would say that based on what we've seen since 1997, we'll likely have blue mold in North Carolina this year,” Main says. “How serious it will be depends on how soon it arrives and the weather.”

Sitting at high-tech weather monitoring systems in Raleigh, Main and his colleagues keep an eye on blue mold movements, with the goal of “staying at least 48 hours ahead of the spores.” They'll issue 500 to 600 forecasts each growing season from March through August. At the head of the operation, Main will move back and forth between his retired status after 35 years of teaching and research as a botanical epidemiologist and that of continuing to provide a valuable service to producers.

By the early 1990s, researchers knew where blue mold came from and how it operated. In 1996, a blue mold epidemic from Cuba to Canada had the tobacco industry in a panic. Following years of progressively worse blue mold outbreaks, the disease blossomed in 1996 on the strength of cool, cloudy and rainy weather. “Suddenly scientists were asking, “Can we predict the movement of blue mold,'” Main says. The answer was, yes.

In its seventh year of operation, the North American Plant Disease Forecasting System issues bulletins on Monday, Wednesday and Friday during the growing season.

Researchers in Raleigh rely on reports from around the U.S. tobacco-growing states as well as Mexico, Cuba and Canada. NAPDF researchers are in the process of expanding the reporting area to include other Latin American countries and the Dominican Republic.

Disease spotters report blue mold occurrences as they happen. “From that information, we look at the weather conditions at their site, which way the wind is blowing and can pretty much tell if the blue mold spores are going to spread to the U.S.,” Main says.

Using National Oceanic and Atmospheric Administration computers, meteorologist Thomas Keever calculates the trajectory of where the spores are likely to be transported. He also evaluates the strength of the spores at the source, the weather at the source, the winds coming from the source, and the weather at the likely destination of the spores. “We look for when the winds will be bringing the spores to the U.S.,” Main says.

Already this season, an “event” in mid-February could have brought spores into Florida and Georgia. Blue mold spores travel in a cloud and the forecasters model the quick movement of the cloud on the winds. Based on what they see, they'll issue a forecast ranging from a high, medium or low risk of a blue mold outbreak, Main says.

J. Michael Moore, University of Georgia tobacco specialist, reported blue mold in a plant bed on March 22. Two acres of plant beds were destroyed. “We think the spores came out of Cuba the third week in February,” Main says. “We had been watching the winds and notified everyone in our system that they should look out for a “moderately severe blue mold dispersal from Cuba.”

“The whole idea is to stay at least 48 hours ahead of the spores,” Main says. “If you can see that blue mold is going to be in your area in 48 hours, you want to spray.”

The same technology used to track blue mold also has applications in determining the sources of potential bioterrorism attacks.

Main often speaks to medical researchers and also presented a paper at a bio-terrorism conference in Washington. Main is a member of a Department of Defense study group on the subject.

In the similar way that researchers track the sources and likely destination of blue spores, they can also help predict bioterrorism events. Researchers can also back track in time to trace the spread of disease spores, which might harm crops, to their source.

Main says the NAPDFC is able to provide the government with maps and evaluate the risk of bio-terrorism. “Just as in the case of blue mold, we can get out in front of the problem.”

While blue mold may not represent a life-threatening scenario for tobacco producers, it is life threatening to their crop and livelihood. That's why knowing when it could be a problem is so important to producers.

“Generally speaking, blue mold is more of a serious problem in the mountains where there are cooler temperatures and fog and rain,” Main says. “But last year, it was a very serious problem in flue-cured country.”

Blue mold is a fungus that will only attack tobacco. Microscopic spores land on the leaf and germinate like seeds. The spores grow inside the leaf for seven days, and then appear in lesions on the underside of the tobacco leaf about the size of a dime or a quarter. One spore can produce a lesion. In the span of a week, millions of spores are produced. “In the terminology of epidemics, when favorable conditions exist, it can double every four days,” Main says.

“A farmer doesn't have much chance to catch it once it gets started,” Main says. “If blue mold gets in a greenhouse, it's probably infected the whole greenhouse and the ones next to it.”

Tobacco experts recommend preventative fungicide treatments.

“Prevention during plant production is very important,” says Paul Shoemaker, North Carolina State University Extension plant pathologist. In the greenhouse, producers can use Dithane at one teaspoon per gallon or one half pound per hundred gallons of spray. Treatment is recommended at least every five days, Shoemaker says.

In the field, the best strategy is to start spraying as soon as a blue mold advisory is issued, Shoemaker says. “Some farmers hear the forecasts and don't take them to heart,” Shoemaker says. “Producers should begin spraying immediately if blue mold is reported to likely be headed to their county.”

Preventative treatments include Acrobat MZ at 2.5 pounds per hundred gallons of spray. “When the plants are small, it takes 20 gallons of spray per acre,” Shoemaker says. As the plants get bigger, spray volume can be increased up to 100 gallons per acre.

Actigard, which received registration last season, is a material that activates the plant's resistance to blue mold. It's recommended for two applications, 10 days apart when the tobacco plants are 18 inches tall. In burley, research has shown that when it's used before the plants are 18 inches tall, stunting and yield loss may occur, Shoemaker says.

If blue mold is forecast before the plants are 18 inches tall, another product will need to be applied.

Ridomil is no longer recommended for blue mold since the disease has become resistant to the product, Shoemaker says.

The blue mold forecast is on the Internet at

The forecast is also available toll-free in North Carolina at 800-662-7031. Outside of North Carolina, the number is 888-835-2583.

“The forecast is updated every day,” Main says. “When blue mold gets serious and advancing rapidly, we even look at it on Saturday and Sunday.” Last year, the Website had more than 400,000 hits to this decision support system for the control of blue mold.

“Based on the blue mold forecasting center, farmers have a better idea of when they should spray and when they don't need to spray,” Main says.

Between the hectic schedule of monitoring the blue mold situation in the U.S., Main finds time to catch up on his fishing. After all, he is retired.

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