A cooler, rain-soaked spring in parts of the Southeast pushed peanut planting dates later than usual, a factor that can impact the type and incidence of disease growers experience throughout the remainder of the season.
“Planting dates definitely make a difference in peanut diseases, both in the type of disease you have and the pressure,” says Austin Hagan, Auburn University Extension plant pathologist.
If you plant early, you’ll have less leafspot and less rust pressure, says Hagan. But if you have a field with a history of white mold disease, you’ll have more disease pressure when you plant from late April to the first of May. There’s also a higher risk of tomato spotted wilt virus, he adds, but with current varieties, the disease pressure to date is minimal, even in mid-April planted peanuts.
“The later you plant, the more leafspot will intensify. Also, the later you plant, the less white mold you’ll have because the crop is maturing out at the end of September and into October when soil temperatures are a lot cooler,” says Hagan.
This growing season began much like last year in Alabama, with cooler and wetter-than-normal weather conditions. This was followed by plentiful and sometimes excessive rainfall throughout the course of the season.
“Whenever you talk about a growing season with 60 to 80 inches of rain on peanuts, you’d expect some serious disease issues, especially with leafspot, but that really wasn’t the case last year. But there was a lot of thrips damage this spring but not much tomato spotted wilt virus in Alabama peanut fields,” he says.
Every new generation of peanut variety that comes down the pike seems to be better than the previous ones at managing TSWV, says Hagan.
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“A few years ago, we started growing Georgia Green and thought they were the greatest thing on earth. But the newer varieties we have now are much better. There was early and late leafspot because of all the rain in 2013, but it just wasn’t as bad as it could have been.”
Weather plays a major role in both leafspot disease and white mold, notes Hagan. “One thing that may have slowed leafspot and took out white mold in some fields was cool temperatures. It was cooler in 2013 than in 2012, and we had moisture in the soil constantly.
To get white mold going, we need a fluctuation between wet and dry cycles, and we need higher soil temperatures. It needs to get up into the mid- to upper 90s every couple of days, and we need to have nighttime temperatures in the high 70s. Root-knot nematodes also showed up this past year, and having a lot of moisture in well-drained soils is good for their development.”
Many fungicide options available
As for fungicides for controlling peanut diseases, there are a lot of products on the market now and others coming in future.
“We have both brand-name and generic materials. If you’re looking to spend less money and still have a full-season program, we have generics available that’ll fill in the blanks. If you want to use some of the higher-end products and have a little more efficacy, we have those also, but it’ll cost a little more.”
There are new ones this year, and there will be changes over the next two years because products that were strictly name-brand will become available in generic formulations, says Hagan. As a result, the cost of those materials will be less.
“Syngenta has a product called Alto that they’re marketing this year to use as a tank-mix partner with Abound. When we were looking at triazole fungicides about 15 years ago, Alto performed very well, and it was very effective against white mold.”
Muscle ADV by Sipcam is a pre-mix of tebuconazole and chlorothalonil. We like to see this mixture because there is some question about resistance to tebuconazole in some strains of leafspot fungi. Adding the chlorothalonil protects it. The generic tebuconazoles still do a pretty fair job against white mold when you consider the cost.”
Custodia from Mana is a combination of azoxystrobin and tebuconazole, says Hagan. It should be available this summer. The patent on azoxystrobin, which is Abound, is scheduled to come off on June 15.
Azaka from Cheminova is another new azoxystrobin product, he says, and Priaxor from BASF is a premimum product with Xemium as an active ingredient.
“The azoxystrobins do have issues in the long term,” says Hagan. “We’ve used some Abound and some Headline in Alabama, and we haven’t had any control failures due to resistance. But once they go generic and the cost comes down, we might have some long-term issues. To protect this chemistry, in the future it might be a good idea to throw in ½ to 1 pint of one of the chlorothalonil fungicides to make sure we avoid putting a lot of pressure on this material as far as efficacy, so we don’t have any control failures. We use azoxystrobin in a lot of crops now, and you never know what’ll happen.”
Tebuconazole materials are still available, and they’re very inexpensive, he says. “They’re pretty effective for white mold, but probably not a top-of-the line material anymore. But if you’re growing dryland peanuts where white mold is not a major issue, and you want some protection, it’ll probably do okay for you. Because of resistance, it does need to be tank-mixed with chlorothalonil to get good leafspot control or at least to insure that you get good leafspot control.
“In Mobile, Baldwin and Escambia counties, we’ve seen that if you apply generic tebuconazole and you get a rain within 24 hours, it’ll be on the ground because it’ll wash off. You get great white mold control, but it just won’t work for leafspot by itself. Since these products are so cheap, we’ve heard stories with other crops that growers are jacking up the rates above what it says on the label. Regulators are out there looking for this, so don’t do it.”
Peanut Rx continues to be an effective program that allows growers to manage their fungicide costs, says Hagan.
“It allows you to put together a prescription plan for each individual field based on factors such as irrigation, cropping history, rotation patterns, variety selection and others. We’ve tested this program and it works. You can reduce the number of fungicide sprays in peanuts, and if you rotate well, the Peanut Rx program will pay off for you.”
Two new products for root-knot nematodes will be available in a year or two, says Hagan. “Nimitz is from Mana and Velum Total is from Bayer. They’re actually fungicides that work as nematicides. In our trials last year with Velum Total, we were not only picking up nematode control but also controlling soil-borne diseases. We’ll look at these materials closer at they get nearer to registration.”