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Soybean fungicides step out

Asian soybean rust spurred fungicides to leap from fringe to mainstream technology. Several companies are further promoting them as a way to boost soybean yields even if Asian soybean rust doesn't strike.

It's all part of programs featuring the use of strobilurin fungicides like Headline and Quadris, manufactured by BASF and Syngenta, respectively. BASF, which calls its program Plant Health, recommends applying Headline at the R2 to R3 stages (full bloom to early pod). Syngenta, which includes fungicide application in its AgriEdge program, recommends applying Quadris at the R3 stage. AgriEdge taps tools like fungicides, insecticides, and seed treatments to boost yields and profits.

Obtaining yield increases via application of strobilurin fungicides in the absence of Asian rust can hinge upon weather conditions, says Wayne Pedersen.

Fungicide applications in both programs are rooted in disease management. However, soybean farmers haven't historically treated the targeted late-season diseases like pod and stem blight and Cercospora leaf blight.

"Growers may not think they have any diseases just by looking out at a field, but that can be misleading," says Marty Wiglesworth, technical fungicide brand manager for Syngenta. "Diseases like these can be nibblers and feeders." By sapping the plant's energy, lower yields ultimately result.

The other component of these programs is how strobilurin fungicides impact plant physiology. Timely applications of Headline can control disease and spur benefits like increased plant growth efficiency, more efficient photosynthesis, and an increased tolerance for stress during the critical reproductive stages, says Rick Chamblee, BASF technical services manager.

"Physiological effects also include things like more efficient water use, better ethylene synthesis, and better carbon assimilation," adds Wiglesworth. Ultimately, these factors help boost yields, he says.

Yields have increased in industry tests. Wiglesworth points to more than 800 comparisons between treated and untreated soybeans that Syngenta has conducted since 1999. On average, Quadris applications at R3 have boosted yields by 4.5 bushels an acre. He adds there are regional differences, with greater yield increases occurring in the South than in Northern states.

Chamblee says Headline applications at R2-R3 spiked soybean yields by an average 9 to 11 bushels an acre in the South and 4 to 5 bushels an acre in the Midwest in over 2,200 on-farm trials. BASF calculates a breakeven of 3 bushels an acre, based on product and application costs of $16 an acre and $5.70 per bushel soybean prices. Much depends upon the year, though, as Midwestern yield increases were smaller due to better growing conditions in 2005. Chamblee says better yield increases result when beans are stressed during part of the growing season.

Fungicides applied in the absence of Asian rust don't always pay off, though. In 2005, Marty Draper, South Dakota State University Extension plant pathologist, compiled 65 university fungicide trials from 13 Midwestern and Northern states. To cover fungicide and application costs, Draper figured a 4-bushel-an-acre yield increase needed to occur.

In these trials, strobilurin fungicides boosted yields above this level one third of the time. Yields rose in another one third of the trials, but not to the 4-bushel-an-acre level. Yields actually decreased in remaining trials.

In baseball terms, you could view this product performance data as a washed-up pitcher just winning one third of his games. On the other hand, a one-third economic payoff could be similar to an all-star .300 hitter. Something is occurring in the absence of disease, points out Draper.

"This is a greater response than just random chance," Draper adds. "But we don't know how to increase the frequency of this response just yet. If we can identify under what conditions yield responses occur, those responses will be more consistent."

Asian soybean rust spurred fungicides to leap from fringe to mainstream technology. Several companies are further promoting them as a way to boost soybean yields even if Asian soybean rust doesn't strike.

Strobilurin fungicide applications to control late-season diseases can be economically viable. Soybean plants treated for anthracnose stem blight on the right at the R3 growth stage yielded 7.3 bushels an acre more than untreated plants on the left in this University of Illinois trial. Returns are more inconsistent in the absence of late-season disease, however.

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