This story is another in a weekly series called "Planting the Seed: Science for the New Millennium." These stories feature ideas and advances in agricultural and environmental sciences with implications for the future.
In the agricultural researchers' battles against the tomato spotted wilt virus, carried by salt-and-pepper-sized insects called thrips, the war never ends. But scientists and farmers enter the new century well armed.
From its emergence in Georgia in 1986 until last year, spotted wilt was growing out of control. At its peak, it claimed $40 million of the state's peanut crop and millions more of tobacco, peppers and tomatoes.
A Glimmer of Hope
Scientists have no cure, but a glimmer of hope of control is reflected in recent results from work by University of Georgia scientists.
In 1998 Georgia farmers saw real progress against the virus. In Georgia's huge peanut crop, the virus's damage was about a fourth of its 1997 peak; 1999 losses were about the same as 1998.
"We have hypotheses," said Albert Culbreath, a UGA plant pathologist. "But we have no conclusive explanation as to why any of these things work.
"It's a much more complex system than most plant viruses, which are seed-borne or mechanically transmitted," he said.
|THRIPS carry the virus that causes Tomato Spotted Wilt Virus.|
"Tomato spotted wilt is vectored by thrips. It replicates in both the plants and the thrips."
Helping Farmers Minimize Risk
In Georgia and Florida, scientists work in a group called S.W.E.A.T. - Spotted Wilt Eradication Action Team. After nearly a decade of work, the UGA scientists from the College of Agricultural and Environmental Sciences found six things that affect the incidence and severity of spotted wilt in peanuts: variety, planting date, plant population, insecticides, row pattern and tillage.
S.W.E.A.T. recommendations go to farmers in a package that was the brainchild of extension entomologist Steve Brown. The UGA Tomato Spotted Wilt Risk Index for Peanuts assigns numbers to the recommendations and adds a correction factor based on previous spotted wilt losses.
The index gives farmers a choice of ways to lower the risk of the virus. The only certainty is that they can't choose just one.
"No one factor is sufficient on its own," said Jim Todd, an entomologist on the team. "It is clear that the combinations are the way to go. And the more of them you use, the better."
Exciting Developments in Fighting TSWV
An exciting development this year could move control in tobacco ahead in giant steps.
Extensive UGA tests show combining two agro-chemicals, imidacloprid and Actigard (R), provided near-complete control of spotted wilt. Imidacloprod is an insecticide primarily used for aphids and flea beetle control. Actigard is a a new plant defense activator.
"Unlike in peanuts, there are no spotted wilt-resistant varieties of tobacco," said Hanu Pappu, a plant virologist in Tifton. "Growers had little or no options to manage the disease until now."
New peanut varieties also show resistance. Georgia Green, a 1995 UGA release, consistently has 50 percent less spotted wilt than is found in susceptible varieties. In Georgia, Florida and much of Alabama, growers planted 95 percent Georgia Green in 1999.
A new cultivar C-99R, developed by the University of Florida, appears even more resistant than Georgia Green, especially when disease pressure is high.
"In situations where a grower is putting together many factors to manage spotted wilt, Georgia Green and C-99R generally perform similar," Culbreath said.
"In situations with early planting or thin stands, though, C-99R shows a bit of an edge," he said. "It's a little more forgiving. It still needs to be combined with as many other factors as possible, though."
The scientists in Georgia, Florida and the USDA see even better genotypes in the evaluation stage.
Continuing to fine-tune the assessment index, scientists learned this year that the twin-row and the conservation tillage efforts are even more effective than they originally thought.
A Long Way to Go, Still
"There's a lot to learn," Todd said. "There's a lifetime of work here for a pile of people."
The results translate into economic and agronomic success for agriculture throughout the Southeast. That's a battle worth fighting.