Growers Looking Beyond The Basics

Experts weigh in on what it takes to control frogeye leaf spot and other diseases that are prevalent in the Mid-South. ‘Magic bullets’ have lost various degrees of efficacy.

Dr. Trey Price discusses tools for soybean disease management with farmers in St. Landry Parish.
Dr. Trey Price discusses tools for soybean disease management with farmers in St. Landry Parish.

Record high soybean yields across the Mid-South are prompting growers and consultants to reevaluate their crop management inputs more closely than ever before.

“We’re achieving yields now that no one would have even dreamed of 15 to 20 years ago,” says Alan Blaine, co-founder of Southern Ag Consulting in Starkville, Miss. “When I first went to work for Mississippi State University in 1987, soybeans were considered a relatively low value, secondary crop. Cotton got all the attention. Now soybeans are exciting.”

Shift in Focus
“It used to be that cotton also got the best ground, the highest inputs and the most intense management,” Blaine says. “That’s not the situation today. All of a sudden, soybeans are being planted on phenomenal ground, and growers who are paying attention to details such as planting date, proper variety selection, disease management, fertility, drainage, etc. are getting yields they couldn’t even imagine a few years ago. I mean, who would have thought we would ever see 52-bushel soybeans?”

As crop value increases, growers are looking beyond the basics of variety selection and planting date for improved yields. Even disease management, which was once almost an afterthought, is now being scrutinized for potential tweaks. This is particularly true when it comes to frogeye leaf spot (FLS) – Cercospora sojina.

The incidence and severity of frogeye leaf spot has grown increasingly problematic in Southern soybean production, partially due to resistance issues. Strobilurin chemistries that were once a “magic bullet” for Cercospora control have lost various degrees of efficacy across the Mid-South.

“We started seeing a decline of strobilurin efficacy on Cercospora leaf blight starting in 2005, and efficacy has been steadily decreasing since that time,” says Dr. Trey Price, plant pathologist with Louisiana State University’s Macon Ridge Research Station, Winnsboro, La. “In 2014, some producers had to retreat more than once with different products to keep it in check.”

Dual Mode of Action
As a result, other active ingredients have emerged as essential components of disease management. In 2014, Gowan Company obtained registration for Affiance Fungicide – azoxystrobin and tetraconazole. Gowan was already marketing tetraconazole under the trade name “Domark Fungicide.”

“The combination makes a lot of sense,” says Craig Sandoski, Gowan’s Southern Regional Development Representative. “The tetraconazole component is where we really fit in terms of Cercospora. When it comes to triazole fungicides, such as Domark, the active ingredient tetraconazole is the most active of the triazoles against frogeye, and the strobilurin component picks up other diseases that would otherwise go unchecked.”

University field trials in Arkansas, Louisiana, Tennessee and Mississippi have shown promising results in initial testing.

“Tetraconazole and other triazoles have been efficacious on FLS in my field trials,” Price says. “Furthermore, triazoles have a less specific mode of action than strobilurins, which lowers the risk of resistance. I only have one year of data for Affiance, specifically, but it was among the most efficacious fungicides on FLS in my trials in 2014. We also had good results with Domark alone last year and in years prior.”

Those results have been documented under moderate FLS pressure, according to Price. Blaine likes the combination because strobilurins are still very effective on other diseases such as aerial blight, stem blight, anthracnose and a long list of others.

“The advantage of Affiance is that it will target more diseases than just frogeye,” Blaine says. “There are a lot of other diseases out there that I call ‘nibblers.’ They’re not readily observable to the naked eye, but they’re working in the background eating away at plant health and yield. A lot of times you don’t notice the effects until the fall. Once you see them, it’s too late.

“Strobilurins are still going to be the base program that we use for now,” he adds. “In combination with tetraconazole, the product works on a wide range of disease problems.”

Mid-South soybean growers usually only apply one fungicide application per season, according to Sandoski. “Frogeye shows up about the time the plant goes into the reproductive stage, so shortly after, they start to make pods at R3. That’s when most of these applications go out,” he says.

“I’m not afraid of frogeye because I know it can be controlled,” Blaine says. “If you pay attention to all aspects of crop management, you can make phenomenal yields with the tools we have available today.”

Gowan Company contributed this article.


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