Trials show preventive fungicides protect yields

With Asian soybean rust pretty much a no-show in the Mid-South in 2005, farmers in the region might not be faulted for forgetting that other soybean growers weren't quite as fortunate.

Although soybean rust spores were found as far north as Canada, dry conditions allowed producers in the Mid-South and Midwest to escape the disease. But treatable levels of ASR did occur in Alabama, Florida, Georgia, southeast Mississippi, North Carolina and South Carolina.

And, while those farmers probably would have gladly passed on that distinction, university researchers and chemical company representatives obtained valuable information about how to combat the disease if it spreads to other parts of the Soybean Belt in 2006.

“This is the first year that we had soybean rust early enough that we could actually conduct trials here in the United States,” says Gary Schmitz, regional technical services manager for BASF.

“Overall, the results were similar to trials we've conducted in South America. The biggest difference may be that Brazil has heavier infestations of rust, and it comes in earlier, at least compared with what happened this past year in the southeastern United States.”

Schmitz drew on fungicide trials in Georgia and Alabama to outline what BASF will be recommending for control of Asian soybean rust and other diseases at a meeting of ag retailers and distributors in Orlando. Recommendations for other companies' products are expected to mirror those in 2006.

Since it's difficult to predict whether Asian soybean rust spores will move from areas where they were found in Georgia and south Texas earlier this year into the Mid-South, plant pathologists are recommending that growers plan to make a preventive application of a fungicide at the R-1 stage of development.

Speakers at the BASF meeting and at other meetings have made a good case that applying labeled fungicides on corn and soybeans will produce benefits; i.e., higher yields, that will offset the costs of the applications whether Asian soybean rust develops or not.

BASF could have three products for use on diseases in soybeans in 2006. The first, pyraclostrobin or Headline, is a strobilurin fungicide that provides preventive protection against a number of diseases. The second is Headline SBR, a combination of F500, the active ingredient in Headline, and tebuconazole, a triazole fungicide that has curative activity for ASR.

The company also expects to receive a Section 18 emergency exemption registration for Caramba, a new product that contains the active ingredient metconazole, a curative fungicide for Asian soybean rust, in time for the 2006 use season.

“Once it is registered it will have the longest residual control of any triazole fungicide on the market,” said Schmitz. “We believe Caramba will fit very well as the second application if two treatments are necessary to manage Asian soybean rust.”

Farmers have two modes of action for controlling Asian soybean rust. The strobilurins (Quadris, Headline) provide preventive, residual control of the disease, but have limited curative activity. The triazoles (Bumper, Domark, Folicur, Laredo, Propimax, Tilt) provide curative activity on existing infections of soybean rust.

Manufacturers have also introduced products that combine both modes of action (Headline SBR, Quilt, Stratego).

One of the key lessons Extension specialists and the chemical companies learned in the Southeast in 2005 was that not only must they evaluate rust control, but they also have to look at soybean yield.

“What we're really after is protecting the yield,” says Schmitz. “Another lesson is that timing is extremely critical with that first application. If you miss it, you can't make up for it later. If you get into a curative situation, you've probably already lost some yield.

“The last thing is that coverage is essential when you're applying fungicides. You need good coverage through the entire soybean canopy.”

Schmitz showed the results of a study conducted by Bob Kemerait, Extension plant pathologist with the University of Georgia, on Group 4.4 soybeans planted on June 2 near Attapulgus, Ga.

Kemerait made a preventive application of the fungicides Headline and Headline SBR on plots in the field on July 18. Asian soybean rust moved into the area around July 26, and Kemerait made a second application of the fungicides on some of the plots on Aug. 9.

The untreated portion of the plots, which were evaluated on Sept. 22, was rated at a disease severity of five on a scale of one to five. The severity rating was almost zero for plots treated with Headline SBR at R-1 and R-3, 1.5 for plots sprayed with Headline at R-1 followed by Headline SBR at R-3 and 3 for plots sprayed with Headline at R-1 only.

Kemerait harvested an average of 40 bushels per acre in the untreated plots vs. 50 bushels in plots treated with Headline at the R-1 stage only and 55 and 58 bushels per acre on plots sprayed with Headline SBR at R-1 and R-3 and Headline at R-1 followed by Headline SBR at R-3.

“As you can see, the two-shot program provided better rust control than a single application, and that's what we would expect,” said Schmitz. “In this situation, rust was fairly heavy, and a second application was needed. More importantly, if you look at the yield, you can see the two-shot program had the highest yields and protected the soybeans the best.”

In another test in Slocumb, Ala., researchers compared applications of Headline and Headline SBR at R-1 followed by an application of Headline SBR at R-3 and two applications of a triazole fungicide.

The first treatment was applied preventively July 13. After rust moved into the area, the second application was made on Aug. 13. The untreated area of the trial had reached 100 percent infestation when the plots were evaluated on Sept. 14. Yields ranged from 20 bushels for the untreated to 35 for Headline followed by Headline SBR at R-1 and R-3.

“If you look at the evaluations for the upper canopy of those plants, you see that the two Headline programs did a very good job of controlling rust,” says Schmitz. “Then looking at the lower canopy, you still had good control of Asian soybean rust. Most important again is looking at the yield. You can see both of the Headline programs did a great job of protecting the yield.”

Based on those and a number of other trials in the Southeast in 2005, Schmitz said BASF will have two general recommendations for soybean farmers in 2006:

  1. If the soybean crop gets to the R-2 or R-3 stage, and rust has not been found in the area, BASF recommends spraying Headline for improving plant health and preventive control of Asian soybean rust. (Apply at 6 ounces per acre with an adjuvant.)

    “You're going to want to continue to monitor those fields, and, if rust moves into the area, and we have the weather conditions that are conducive for continued rust infestations, we may have to consider a second application.”

    In that second application, BASF will recommend one of two different products: Headline SBR, which, has the curative activity of the tebuconazole, or Caramba, assuming EPA grants a Section 18 emergency exemption for its use in 2006.

  2. If rust is already in a field or suspected to be in the area, BASF recommends Headline SBR for the first application.

“It doesn't really matter what stage the soybeans are in at this point,” says Schmitz. “If the soybeans are vegetative and haven't flowered, and you have rust moving into the area, you need to use Headline SBR. There's no need to wait until you get to flowering because, if rust is a threat, you should spray preventively.

“Of course, if you get late in the season and you get out past R-5.5 or R-6, you've already beaten the rust, and you have no need to spray.”

e-mail: [email protected]

Hide comments


  • Allowed HTML tags: <em> <strong> <blockquote> <br> <p>

Plain text

  • No HTML tags allowed.
  • Web page addresses and e-mail addresses turn into links automatically.
  • Lines and paragraphs break automatically.