Peanut disease control arsenal expanded

It’s an ironic twist that the same weather conditions that producer high-yielding peanut crops – warm and wet – also provide an ideal environment for diseases to flourish. Fortunately, the tools are available to minimize the impact. And this year, there are a few new materials to add to the arsenal.

Elast 400 was recently approved for use by the EPA and is being touted as an economical alternative for chlorothalonil for leafspot control on peanuts. “This is an older chemistry that has been used on other crops for years,” says Austin Hagan, Auburn University Extension plant pathologist. “Rates will vary depending on whether you use it as a tank-mix partner or if you use it alone. When used alone, you’d apply Elast three times – in applications one, two and seven of a resistance management program or in a tank mix with Folicur for applications three thru six.”

The fungicide’s active ingredient dodine has been marketed in the United States for about 30 years for the control of diseases of fruits like apples and pears as well as several nut crops. “It is distributed by Aceto Agricultural Products and apparently is very price competitive with generic chlorothalonil formulations,” he says.

Elast is not a seven-spray product like Bravo, Echo or Equis, says Hagan, but you could include it in your program if you’re looking for a value product for leafspot control. When applied alone, Elast 400F may be applied at rates up to 1 ½ pints per acre in 10 to 15 gallons of spray volume per acre for the control of early and late leaf pot diseases on peanut.

Application guidelines for Elast 400F for leafspot control on peanuts are the same as those for formulations of chlorothalonil as well as Tilt Bravo SE, Absolute and Heritage 50W.

“Make the first application of this fungicide between 30 and 40 days after planting. Depending on rainfall patterns, repeat applications of Elast 400F at 10- to 14-day intervals. For the purposes of resistance management, no more than a total of three applications of Elast 400F alone may be made per year. If tank-mixed with another fungicide, the total number of Elast 400F applications may exceed three,” says Hagan.

In 2008, Elast 400F was included in fungicide screening trials at the Wiregrass (WGREC) and

Gulf Coast (GCREC) Research and Extension Centers on the AT3085RO peanut cultivar, he says. At both locations, two applications of Elast 400F at 15 ounces per acre were followed by four consecutive applications of Folicur 3.6F at 7.2 ounces per acre and a final application of Elast 400F at 15 ounces per acre, while two applications of Echo 720 (chlorothalonil) at 1 ½ point per acre were followed by a block of four applications of Elast 400F at 12.8 ounces plus Folicur 3.6F at 7.2 ounces acre and a final application of Echo 720 at 1 ½ pint per acre.

In both trials, fungicide treatments were applied at approximately 14-day intervals and a total of seven applications were made. Leafspot diseases were rated using the Florida 1 to 10 rating scale and white mold damage was determined at digging.

In both studies, says Hagan, Elast 400F replaced Echo 720 in a Folicur resistance management program. The level of leafspot control and yields where stand alone applications where both Elast 400F or Echo 720 bracketed four consecutive applications of Folicur 3.6F in the WGREC trial was similar, he says.

When Elast 400F replaced Echo 720 as a tank-mix partner with Folicur 3.6E, no drop off in leafspot control or yield response was seen at WGREC. While the Echo 720/Elast 400F plus Folicur 3.6F and the Echo 720/Echo 720 plus Folicur 3.6F programs gave better

leafspot control than Echo 720 alone, yield for all of these fungicide programs were similar, adds Hagan.

At the GCREC, Elast 400F was also an effective replacement for Echo 720 in a Folicur resistance management program. Leafspot and rust ratings as well as for the Echo 720/Elast 400F plus Folicur 3.6F and the Echo 720/Echo 720 plus Folicur 3.6F programs did not significantly differ. A significant decline in leafspot and rust control was seen when Folicur 3.6F was applied without an Echo 720 or Elast 400F tank mix partner. Echo 720 alone gave the same level of leafspot and rust control as the Echo 720/Elast 400F plus Folicur 3.6F and the Echo 720/Echo 720 plus Folicur 3.6F programs. At the GCREC, yields were statistically similar for all of the fungicide programs.

“Additional trials need to be conducted to determine how best to utilize Elast 400F, particularly as a stand-alone treatment as well as the influence of application rate and treatment interval on the control of leafspot diseases on peanuts with this fungicide,” says Hagan.

A new formulation of Evito also is available this season, Evito-T, says Hagan. It is a pre-mix of fluoxastrobin and tebuconazole. “It’s more of a leafspot/white mold material with tebuconazole added to the formulation to beef up the white mold control and give a little protection as far as resistance management,” he says.

Many Alabama producers saw a fair amount of pressure from leafspot in 2008, says Hagan. “Rotation has a lot to do with how much pressure you’ll get during the course of a growing season. If you’re in a good rotation, it takes a lot longer for the leafspot to get on your peanuts. If it’s a field where peanuts have never been grown before, you’re not going to have much leafspot pressure. But the next year, if you put peanuts out there, you’ll have pressure,” he says.

Reduced tillage – compared to conventional tillage – will help to slow down leafspot disease, he says. “Reduced tillage certainly won’t control the disease, but it’ll slow it down,” says Hagan.

New peanut varieties are now available to growers that have some resistance to leafspot, he says, and that’s a big help in reducing the amount of damage in a crop. GA-03L, Tifgard and FLA-07 all showed good resistance to leafspot in trials, says Hagan.

Some growers also saw considerable pressure this past year from white mold, he says. “If you have a history of vegetable production – particularly watermelons – you’ll see some white mold in your fields. In some of our trials, Tifgard, GA-03L and AP-3 had virtually no white mold. Basically, that translates into higher yields. We get 400 to 600 more pounds per acre yield difference when we drop out the leafspot and white mold damage.”

The “very basics” of peanut disease control, says Hagan, still include – where you’re planting into a field where you’ve had peanuts in the past – to start spraying 30 to 40 days after planting, and re-apply every 12 to 14 days, based on weather patterns.

“If it’s raining a lot, you may have to shorten the intervals. If you’re out in the field spraying, especially a material like Folicur, you may have to cut back to seven days. If you want to save a little money on your leafspot programs, you can band the first and second fungicide applications over the row middles. There’s no point in spraying the bare ground between the seedling peanuts – it’s just a waste.”

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TAGS: Peanuts
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