Peanut diseases a given for Southeast

It’s one of the harsh realities of growing peanuts in the Southeast — you will have disease problems.

“The same type of weather and climate that helps you grow peanuts so successfully in the Southeastern United States also makes it difficult to control diseases,” says Bob Kemerait, University of Georgia Extension plant pathologist.

Fungicide programs, he adds, constitute the single most expensive input a grower will have in peanut production. “It’s not seed, insecticides or herbicides. You spend more in fungicides than perhaps anything else — that’s the bad news. The good news is the tremendous value you receive from controlling diseases. We could not make the desired yields and grades without these programs,” says Kemerait.

The No. 1 problem for peanut producers in Georgia in 2007 was drought rather than any particular disease, he says. “Somehow, Georgia growers managed to yield 3,000 pounds per acre, and I’m not sure how they did it. Fortunately, tomato spotted wilt virus was not a factor. In fact, since 1994, this past year was one of our lightest years for tomato spotted wilt virus.

“That was good for 2007. The problem with 2008 is that growers may become complacent, thinking we don’t have to worry anymore about tomato spotted wilt. But no matter what happened last year, 2008 could be a bad year. Be prepared for a bad year of tomato spotted wilt virus if you don’t manage carefully,” says Kemerait.

The most damaging disease across peanut fields last year was white mold, he says. This is puzzling to some — considering the drought in 2007 — because white mold is a fungal disease that needs water.

“But the primary driving force behind white mold is high soil temperatures, and we certainly saw those this past year. If you don’t have a lot of moisture above ground, you still can have white mold underground,” he says.

One tool for managing and controlling diseases of peanuts, says Kemerait, is Peanut Rx. The University of Georgia Tomato Spotted Wilt Virus Risk Index and the Peanut Fungal Disease Risk Index were successfully combined in 2005 into the Peanut Disease Risk Index for peanut producers in the Southeastern U.S.

The Peanut Disease Risk Index, developed by researchers and Extension specialists at the University of Georgia, the University of Florida and Auburn University is now officially know as Peanut Rx.

“Peanut Rx is a seal of approval, saying that these are fungicide programs we have found to be effective. We’re looking for ways to minimize tomato spotted wilt virus, leafspot, white mold and limb rot,” says Kemerait.

A few changes have been made to Peanut Rx 2008 from the 2007 version, says the plant pathologist. Those changes can be found in the cultivar/variety section of the index, in the planting date section, and in the plant population section, with many of the changes being directly related to white mold control.

“One of the changes is that we have bumped up the susceptibility or the risk points assigned to some varieties for white mold. This was simply because some of the newer varieties have so much better resistance to white mold. So we try and differentiate between those and older varieties like Georgia Green.

“Another change is that a number of new runner varieties have been included in the cultivar/variety section of the index,” says Kemerait.

In addition, he explains, white mold appears to have more impact on earlier planted peanuts (prior to May 1) and the risk points for that period have been increased from “5” to “10.” “Since soil temperature drives white mold, if you plant early, you run a greater risk of having white mold later in the season. If you plant later, that risk is less.”

The final change, he says, is an added risk for white mold in stands of more than four plants per foot — this risk is given “5” points. “How does white mold move through a field? It goes from one plant to the next. An increased stand is crucial to maintaining control over tomato spotted wilt virus, but have more plants per foot of row actually increasing your risk of white mold.”

Peanut Rx, says Kemerait, gives growers the opportunity to learn how to manage disease risks in their fields. The program also offers prescription programs rather than a one-size- fits-all program.

“If you’re a grower who wants to maintain leafspot control, white mold control and limb rot control while making good yields and maximizing profits, this program is for you. We want to insure adequate control in every field and maintain yields, but we want to maximize your profits.”

Syngenta is the first company to partner with the universities on this prescription program, he says. “They have specific programs for growers according to their individual field situations.”

e-mail: [email protected]

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