Some Arkansas fields at risk Soy rust advanced quickly in Mid-South

It's the 11th hour for many Arkansas growers invaded by soybean rust infestations on virtually every field planted late. If you farm in Arkansas and your beans are at the R-4 to R-5 stage — spraying a triazole fungicide is highly recommended, stresses Scott Monfort, University of Arkansas Extension plant pathologist in Lonoke, Ark.

Beans in the R-1 to R-4 stage should have a combined application of strobilurin and a triazole.

“We are strongly encouraging producers in all soybean growing counties in the state to consider treating soybeans in the R1 to late-R5 stage for soybean rust if they have good yield potential,” says Monfort.

“About 600,000 acres of soybeans have been sprayed or will be sprayed. That's about half of our late-planted beans.”

There are more than 3.4 million acres of soybeans in Arkansas. And most have escaped the potential for damage, due to maturing into the R-6 stage before rust struck. But with one-third of the state's crop planted late, rust will likely be a threat through mid-October for many acres, says Monfort.

According to the USDA Soybean Rust Integrated Pest Management Pipeline Web site, as of Sept. 21 rust had been found in nine states and 206 counties and in two states and five municipalities in Mexico. The threats have been there in past years, but never when beans were so late in the growth stage.

Up to this year, most growers have dodged the rust bullet in Arkansas, as well as in Louisiana, Alabama, Texas and other states southern states. All growers in Mississippi have escaped rust damage. Several southern growers have had to treat fields with fungicide applications. But nothing like this year in Arkansas.

Monfort is experiencing the kind of year he and others have dreaded ever since rust was discovered in the U.S. about seven years ago. At least 31 Arkansas counties are facing rust infestations. He and associate Amy Carroll nearly have their eyes glued to microscopes to examine rust infestations on hundreds of samples sent to the Lonoke pathology laboratory.

Trey Koger, Mississippi State University Extension soybean specialist in Stoneville, Miss., adds that about half of that state's counties have rust. “But about 95 percent of our beans are far enough along (into the R-6) stage and likely won't be affected by rust like those in Arkansas,” he says.

Monfort sees no let up and fears that continued rainy spells will hamper spraying programs even more than those wet spells in early September.

“The disease is continuing to develop and spread throughout much of the Arkansas Delta and is not showing any signs of slowing down,” he says. “The prolonged cool, cloudy and wet conditions have allowed rust to become and remain very active and aggressive.

“This stuff is really moving along. We are beyond the purely preventative stage. We're beyond using only strobilurins. It's mostly all triazoles to prevent and cure any rust problems.”

Monfort points out that many growers are looking at outstanding crops and above average yields. So rust treatments are at the top of their management list if there's a possible threat.

Headline and Stratego are preventative fungicides that are used by some growers to head off disease problems in general and promote better growth. But they may not be as effective in the current situation, says Monfort.

He recommends these fungicide treatment rates: triazoles — Alto, 4 ounces per acre; Laredo, 4-8 ounces; Folicur, 3-4 ounces; Orius, 3-4 ounces; Topguard, 7 ounces; Domark, 4-5 ounces; Punch, 3-4 ounces; ProLine, 2.5-3 ounces; Tilt, 4-8 ounces; and Bumper 4-8 ounces Strobilurin/triazole combinations: Quadris Xtra, 4-6.8 ounces; and Quilt, 14-20.2 ounces.

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