Georgia peanut producers saw the lowest incidence of tomato spotted wilt virus this past year since the early 1990s, but it's no reason to become complacent about the disease, says Steve L. Brown, University of Georgia Extension entomologist.
“Tomato spotted wilt virus came into our fields late in the season, and some fields started turning yellow,” says Brown. “But weather conditions were good enough early in the year that most growers were able to set a good crop, and we don't think the disease hurt us too much. We estimate a total loss from tomato spotted wilt virus of about 1 percent in Georgia's 2001 peanut crop.”
The reduced incidence of the disease, however, is no reason for growers to minimize the potential of tomato spotted wilt, he says. “With the minimum impact most growers saw last year, there's a danger of growers becoming complacent about tomato spotted wilt. Many growers may put the disease on the backburner in terms of priorities, but that would be a mistake.
“Our check plots continue to show high levels of the virus. We saw plots in Tifton this past year with 80 to 90 percent incidence levels. I would strongly caution growers not to go back to susceptible varieties or planting in April. Tomato spotted wilt still has the potential to be our primary disease problem on peanuts in Georgia,” says the entomologist.
A big reason Georgia peanut growers continue to reduce their risk to tomato spotted wilt virus is that most of them are following the recommendations of the University of Georgia risk index.
The index, first developed in 1996, combines what is known about individual risk factors into a comprehensive but simple estimate of tomato spotted wilt risk for a given field. It assigns a relative importance to each factor so that an overall level of risk can be estimated.
“Our last survey revealed widespread adoption of multiple practices recommended by the risk index,” says Brown. “Of course, almost all Georgia growers are planting the Georgia Green variety, and that's recommended by the index. But growers have to put several of the risk index factors together to truly reduce their susceptibility to tomato spotted wilt.”
Many growers are following the planting date recommendations contained in the index, he says, which is evidenced by only 4 percent of Georgia's 2001 peanut crop being planted during the month of April. “That's the lowest percentage of planting in April we've seen in a long time.”
Many Georgia producers also are planting in twin rows to reduce their risk to tomato spotted wilt virus, notes Brown. “Forty to 50 percent of Georgia growers planted their peanuts in twin rows in 2001. We're also seeing an increase in the number of peanut acres being strip-tilled. Our test plots have shown good and bad results with strip-tillage peanuts. A grower's success will depend on several factors, including soil type.”
Minor changes to the risk index for 2002 include adding three new varieties, he says. “We added Perry — a Virginia-type peanut — and placed it in the 35-point category. We don't grow many Virginia-type peanuts in Georgia, but anyone who has a special contract might want to take a look at Perry.
“We also added AT-201 and made a new category of 25 points for this variety. AT-201 was available last year, but we wanted one more year of data before assigning a risk number. A third addition is Georgia Hi-O/L, a high oleic variety, which we placed at 20 points. It's expected that there will be limited quantities of this variety for 2002 planting.”
Improved varieties appear to be the best bet for controlling tomato spotted wilt virus in the future, says Brown. “We're now at the point to where more improved varieties is our best answer for reducing the risk to the virus. I don't see anything else on the horizon that will alter the index considerably.
“Some varieties currently in the pipeline are very good, with much better resistance than what's available today. Their success depends on their agronomic traits, including grade, quality and yield. Enough of these new varieties show good tomato spotted wilt resistance that we should see a steady improvement over the next five to six years.”
A low index value, says Brown, does not imply that a field is immune from virus losses. Losses due to tomato spotted wilt virus vary from year to year. In a year where incidence is high statewide, even fields with a low risk level may experience significant losses, he adds.