White mold doesn’t appear to be moving anytime soon from its position as the No. 1 disease threat of Southeastern peanuts, but new options for controlling it continue to become available, says Bob Kemerait, University of Georgia Extension plant pathologist.
“White mold is the No. 1 disease we face in Southeastern peanut production. It’s not the only important disease, but white mold, stem rot or whatever you want to call it, is a critical factor, and we spend millions of dollars to manage it each year,” said Kemerait at this year’s Georgia Peanut Farm Show in Tifton.
In 1994, peanut producers received a proverbial game changer in the form of tebuconazole sold as Folicur, he says. This was followed by azoxystrobin or Abound and Moncut or flutolanil.
“Think about the tools we now have available. Bravo came out in the early 1970s, and it was a game-changer as far as leaf spot control. Prior to Bravo and prior to the ability to keep leaves on the plant, white mold was not as big of a problem. But now that we can keep the crop healthier, white mold has exploded as far as importance. We’ve found that traditional leaf spot materials like Bravo – and certainly Benlate – increase the threat of white mold. What we did to control leaf spot created more and more problems with white mold,” he says.
Changes since 1994
So what has changed in terms of white mold control since 1994, and what should growers consider going into the 2014 growing season?
The basic foundation hasn’t really changed since 1994, says Kemerait, and it includes practices such as rotating, planting more resistant varieties, and using the appropriate fungicide program.
“But one thing that has changed is Peanut Rx. It started out as the tomato spotted wilt virus risk index and now includes white mold. It allows you to take all of the components like rotation, new varieties, seed spacing and planting dates and see how they affect white mold. I’d recommend that you look at this and see what factors you can improve upon to reduce your risk not only to white mold, but to leaf spot and tomato spotted wilt as well.”
Another change has been breeding for resistance, he adds. “It once was just a dream, but we’ve gotten more and more resistance to tomato spotted wilt virus, and we’re getting more resistance to leaf spot diseases.
“The good news is that our breeders continue to bring better varieties to the table. One of those is Georgia-12Y. It is better than Georgia-07W for having white mold resistance, and it has higher yield potential. So when you’re using the risk index or Peanut Rx, you can look at the varieties that are available and see how their resistance compares to favorites like Georgia Green or Georgia-06G. The combination of improved varieties coupled with the use of Peanut Rx allows you to come up with a system of improved white mold control.”
Tebuconazole is on the market, and it’s available at a bargain price, says Kemerait.
“That’s a problem for me, but in some ways it’s a good problem. There’s not a grower in Georgia who doesn’t need to treat for white mold, and using tebuconazole may be a good option. It may be the best option in some non-irrigated fields.
“The problem is that we’re overusing it. Some growers will ask, “Why use 7.2 ounces (the labled rate) when you can put out 14 or 21 ounces? Why spray four times when you can spray seven times cheaper than you could spray Bravo 10 years ago?” We’re overusing a class of chemistry.”
But as a grower, you might make more money by spending more money, he says. “There may be fungicides out there that are better for white mold in a tough situation. They are better, and you’re missing an opportunity if you simply do what you’ve always done. If you stick with only what you’ve done since 1994, than that’s what you’ll always get.”
Other white mold fungicides likely to be available to peanut producers for the first time in 2014 include Priaxor from BASF and Custodia from Farmoz or Mana – a combination of azoxystrobin and tebuconazole.
Different levels of risk
In 1994, growers were told to begin spraying peanuts approximately 30 days after planting, earlier if it was raining, to stay on a 14-day schedule, and to finish after seven to eight fungicide applications.
“Since that time, we’ve learned that there are different levels of disease risk in a field; those companies supporting Peanut Rx with prescription fungicide programs will say that you had better spray at least seven times if you’re at a high risk for white mold. But if you’re at low risk, we now say you can spray as few as four times as long as you stick with specific programs.”
Growers now have more fungicides than ever and better fungicides, he says. “But one thing that has not changed is that since the period from 1994 to 1996 – when Moncut, Folicur and Abound were introduced – we do not have a new class of chemistry. All of our new fungicides for white mold control fall within the triazole class, the strobilurin class or the SDHI class. We’ve got better chemistries and new chemistries, but we have the same classes. We need to protect what we have, because too much use of any one class may ultimately result in fungicide resistance and loss of efficacy to the disease. We’ve already seen resistance develop to Folicur or tebuconazole on leaf spot disease.”
One of the most important things that’ll happen to peanut growers in 2014 is that azoxystrobin sold as Abound will go off-patent.
“And I don’t know if that’s a good thing,” says Kemerait, “because azoxystrobin is extremely sensitive to resistance development. It’s one of our most important classes not only in peanuts but in other crops as well. If we develop resistance to azoxystrobin in our peanut fields, other fungicides will take a hit. Since 1994, we’ve had the strobilurin chemistry brought to peanut farms. If we misuse it in 2014 and beyond, other chemistries will be affected.”
Application techniques change
One of the most difficult factors in controlling white mold is how to get the fungicide through the dense canopy of leaves to the real target- the limbs and crown of the plant, says Kemerait. In 1994, growers broadcast their sprays, spraying every 14 days and using increased pressure to get the spray where it needed to be. Adds Kemerait, “Growers throughout the southeast have really benefitted advances in application technology from Dr. Tim Brenneman’s program at the University of Georgia in Tifton.”
“A relatively new innovation – if we can get growers to get up early enough or stay up late enough – is to spray peanuts at night. At nighttime, the leaves of the peanut plant are folded up and you get better spray deposition. You get the fungicide to the crown of the plant. And when those leaves open during the daytime, they are protecting the applied fungicide from ultraviolet degradation.”
Yield differences in some fields between daytime and nighttime spraying have been as much as 1,000 pounds per acre, he says.
In 1994, says Kemerait, growers began their fungicide spray program for white mold 60 days after planting.
“They still do that, but as of 2011-2012, we began recommending that growers who had white mold problems should start earlier. Spraying a young plant sets the foundation for a good white mold program. Where white mold is severe, we’ve seen that you can get season-long benefits from starting earlier. It’s easy for me to say that you need to put a 6-inch band over 21-day peanuts or a 10-inch band over twin rows, but that’s not easy when you’re running 3 to 6 mph over a field. But the opportunity is there. Early emergence banded applications three to five weeks after planting can be very important where white mold is a problem.”
While white mold was not as severe in 2014 as some predicted, growers still saw benefits from early emergence applications, says Kemerait.
“The cool temperatures last year precluded much early season white mold. If you’ve had white mold problems and you’re thinking about making early emergence applications, look at the strategies for putting it out and anticipate the weather patterns. A cooler early season means you probably won’t have as much of an early season white mold problem.
“If you’ve had a problem with white mold, and you’re not set up to do the early emergence or in-furrow application, we already have the tools to start a white mold program at 40 to 45 days; perhaps by broadcast applications of tebuconazole mixed with your leaf spot fungicide. Then, you can bring the big guns – the more powerful, newer fungicides – at 60 days in your block program.”