The only certainty about tomato spotted wilt virus is that it's continuously changing, offering new challenges each year to growers and researchers alike. Georgia peanut producers experienced an average yield loss from the disease of 7 to 7.5 percent this past year.
“We've learned enough to know we're shooting at a moving target when it comes to tomato spotted wilt virus,” says Steve L. Brown, University of Georgia Extension entomologist.
Pressure from the virus was more severe for Georgia's peanut growers this past year than it has been since the late 1990s, says Brown. “It was certainly up from the 4-percent yield loss we saw in 2004 and the 1-percent loss in 2003. There were significant losses in many fields,” he says.
Even some growers who followed the University of Georgia Peanut Disease Risk Index were hit hard by the virus in 2005, says the entomologist. “We were a little disappointed in on-farm trials of the index this past year. But the components of the index are still good, and we'll continue to monitor it and make changes as needed,” he says.
There have been very few changes to the 2006 Peanut Disease Risk Index from the 2005 version, says Brown. All of the changes that have been made can be found in the cultivar/variety section of the index.
For example, older varieties such as Florunner and Southern Runner that no longer are planted have been removed from the index. More importantly, the number of points assigned to some varieties in a disease category has been changed.
The number of points assigned to Georgia Green and other varieties in the spotted wilt category has been increased from 25 in 2005 to 30 in 2006. This change does not mean, says Brown, that Georgia Green and the other varieties are becoming less resistant to spotted wilt. Rather, it is an indication that the newer varieties that have been released in recent years have significantly greater resistance to the disease, and that the old point scheme has had to be adjusted to reflect the improved resistance.
As in the previous versions of the disease index, growers will note that attention to variety selection, planting date, plant population, good crop rotation, tillage, and other factors can have a tremendous impact on the potential for disease in a field.
“The plant population component is very strong and is one of the most consistent components of the index,” says Brown. “I'd encourage peanut growers to do everything they can to get a good stand. We recommend four plants per foot of row, and the recommended seeding rate is six seed per foot or row. Make sure you use good quality seed, and make sure your soils are warm when you plant. The twin-row component of the index also continues to be strong.”
The University of Georgia Tomato Spotted Wilt Index and the Peanut Fungal Disease Risk Index were successfully combined in 2005 to produce the Peanut Disease Risk Index for peanut producers in the Southeastern United States. The Risk Index has been fully reviewed and updated by authors in Georgia, Alabama and Florida and is based on data and observations from the 2005 production season.