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Few changes made in peanut spotted wilt risk index

Georgia peanut producers experienced more than their fair share of production problems in 2006, but at least tomato spotted wilt virus wasn’t one of them.

However, growers should avoid letting down their guard just because this past year was a relatively light one for the disease, says Albert Culbreath, University of Georgia plant pathologist.

“It’s easy to forget how bad it can be,” he says. “It’s not uncommon to have a light-pressure disease year following a heavy-pressure year. Just because you didn’t have a problem with the disease one year doesn’t mean you won’t have a problem with it the next year.”

Pressure from the virus was relatively light this past year, with an estimated yield loss of 2 percent to 2.5 percent. Of course, there were plenty of other problems with most Georgia producers experiencing dry weather conditions throughout the 2006 growing season. “There were some hot spots for the disease, and some spots we just can’t explain. But if we had had a good season, then tomato spotted wilt wouldn’t have been much of a problem,” says Culbreath.

There have been a few changes to the tomato spotted wilt virus portion of the 2007 Georgia Peanut Disease Risk Index from the 2006 version, he says. All the changes that have been made can be found in the cultivar/variety section of the index and in the planting date section.

“Specifically, a number of new runner varieties have been included in the cultivar/variety section. Also, tomato spotted wilt virus appears to have had less of an impact on later planted peanuts — in mid-May and June — than in the past. Therefore, the risk points associated with later-planted peanuts have been reduced accordingly in the 2007 index.

“In my test, we saw a very strong tillage effect this time. We’ll be taking a harder look at this next year. There seems to be more value in using strip-tillage because there’s less tomato spotted wilt virus,” he says.

Researchers also are on the alert for resistance to tetraconazole, which is used for leafspot control, says Culbreath. “It doesn’t appear to be in every field. We’re just now trying to get a grip on the extent of the problem. We saw it more in growers’ fields after leafspot was breaking through later in the season. It’s definitely a concern.

“A lot of tetraconazole is used for white mold and leafspot. We see no indication of a decreased effectiveness in soil-borne diseases. But there’s a definite shift towards resistance in that fungicide class,” he says.

In addition, researchers and Extension specialists are working on an integrated approach to multiple disease control, he says. “Tillage is showing good suppression of leafspot early in the season, so we’re looking at possibly reducing fungicide inputs with tillage effects.

“The variety Georgia 03L has looked strong in reduced input tests. It is resistant to leafspot, tomato spotted wilt virus and white mold. It’s a medium-maturity peanut. Other varieties also have resistance to a multitude of diseases. Attaboy, which was just released, has a good multiple disease resistance package. There are many new varieties, and we’re trying to keep up with all of them, but that’s a good problem to have.”

The increased interest in corn production for 2007 could be very helpful for peanut production from several standpoints, says Culbreath. “If growers can get corn in a profitable position and use it in rotation with peanuts, then that ultimately would be very good for the peanut crop.”

Varieties continue to offer the best hope for battling tomato spotted wilt virus, he says. “We conducted a two-year test comparing AP-3 with Georgia Green, planted the last week of April or the first week of May. AP-3 has enough resistance when combined with other factors that we might be able to plant it outside that optimal window. Using the optimal planting window is still a valuable tool for reducing your incidence of tomato spotted wilt. But some growers don’t want to or can’t plant in that later window. AP-3 might allow growers to move their planting into late April or early May. When combined with other factors, this may give growers some flexibility.”

Researchers will continue to fine-tune the disease risk index as more disease-resistant peanut varieties become available, he says. As this occurs, other factors in the index might not have as much of an impact, he adds.


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