Georgia peanut producers enjoyed an abundance of good fortune in 2003 — plentiful rainfall, record-high yields and the lowest incidence of tomato spotted wilt virus since 1990.
“We did see some late-season tomato spotted wilt virus showing up in farmers' fields, and it was easy to spot from the typical yellowing symptoms,” says Steve L. Brown, University of Georgia Extension entomologist. “But it didn't appear to hurt our yields since it was so late in the season.”
The University of Georgia Tomato Spotted Wilt Virus Index has helped Georgia growers significantly in their continuing battle against the potentially devastating virus. Looking ahead to the coming growing season, Brown says there will be few changes in the index for 2004.
“The only thing changing for this year is the addition of some new varieties,” says Brown. “We added AP-3 at 10 points and GA-01R at 15 points. Everything else is the same. We didn't see any reason to change anything else.”
Researchers did come up with a table this year to help growers better understand the concept of a planting date window, he says. “It's a way for growers to see how the planting date window changes and other factors change. Many growers were saying they would like to plant peanuts earlier, but the index told them they couldn't plant until May 11. The index actually states that May 11-May 25 is the lowest risk time for planting.
“But if you do other things and plant some of these improved varieties, you still can have low risk and can get into the low-risk category by planting anytime in some situations. In other situations, you can't get into the low-risk category no matter what you do. It depends on other factors.”
The 2003 Georgia peanut crop probably was the latest planted crop in recent history, notes Brown, with less than 2 percent of the peanuts planted in April. Despite the low incidence of tomato spotted wilt virus this past year, the virus still is present in Georgia fields, says the entomologist.
“In situations where we intentionally do everything to create a high-risk situation, we're still seeing heavy virus pressure. We contend the pressure is still there. But because of what growers are doing, the actual incidence of tomato spotted wilt virus is really going down.”
Improved peanut varieties remain one of the best weapons against the virus, he says. “Everything that has been released in the past few years has been resistant to the virus at the Georgia Green level or better. Some of the newer ones are considerably better in terms of resistance than Georgia Green. DP-1 and AP-3 are pegged as the best in our index.
“All of these varieties have their own individual agronomic characteristics, and a grower must choose based on things other than tomato spotted wilt virus. But, if those varieties fit into a grower's program, he can drastically reduce the incidence of the disease in his fields.”
Many improved varieties are in the research pipeline, says Brown. Some of the newer varieties have added characteristics such as resistance to CBR, leafspot and white mold. “There's quite a package of disease resistance being incorporated into these varieties.”
Other components of the risk index, such as reduced tillage and twin rows, continue to be confirmed as lessening a grower's risk to the virus.
“But whenever we get one of these very good improved varieties, these other effects can be minor. In other words, it's difficult to show a difference between twin and single rows with respect to tomato spotted wilt virus when you're using a variety like DP-1 that's planted on May 20. You'll have such a low level of virus that you won't see a big effect from row patterns and tillage.”
Growers should keep in mind that the risk index point total is what counts the most, says Brown. “Don't get hung up on an individual factor within the index. Your cumulative total is very important. You don't have to do everything in the index, but we'd like to see growers at 65 points or less. At that point total, we don't think you'll have a big problem with tomato spotted wilt virus.”
Georgia growers finally saw the end of a multi-year drought in 2003, and the plentiful rainfall probably helped to lower the incidence of tomato spotted wilt virus, says Brown.
“We don't fully understand the effects, but we know that rainfall in the spring is not good for thrips. Thrips prefer dry weather conditions during the spring. Rainfall this past spring probably helped to drive down thrips populations. We had fairly heavy pressure in mid-May, but it was very brief. It lasted for only a week or two, and we saw generally light pressure throughout the remainder of the season.”
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