Last summer, Matt Hughes got defensive. With soybean prices at record highs, it made sense to hang on to every bean.
"The late planting season coupled with moist conditions seemed the perfect situation for disease,” Hughes says. "I crunched the numbers and came up with a 2 bu. per acre break-even for one fungicide application. I considered it an insurance policy given the price of soybeans at the time,” he says.
Until a few years ago, foliar fungicides were mostly an input for the most disease-prone southern states. But economic conditions, coupled with claims of plant health effects—longer green leaf retention, delayed plant senescence, improved carbon dioxide assimilation, increased water use efficiency and increased stress tolerance during flowering and pod fill—kicked up a fungicide frenzy.
"The discovery of soybean rust in 2004 started an evolution,” says Randy Myers, Bayer CropScience fungicide product manager. "As growers learned about rust, they also became more aware of other fungal diseases and the products that control them.”
Mississippi State University Extension plant pathologist Tom Allen says that in the South, the timing coincided with growers realizing the economic importance of soybeans. "Managing soybean rust is a different decision than managing other diseases,” Allen says.
"Today, approximately 65% of our soybean acreage receives a routine foliar fungicide application [typically containing a strobilurin] around the R3 growth stage to control the little things that collectively rob us of yield,” he says. "We'll see fungicide use continue to increase this year as more cotton acreage is replaced with soybeans and we have more bean-following-bean acreage.”
The practice is less clear-cut farther north. Foliar diseases, such as brown spot, frogeye leaf spot, Cercospora leaf blight, powdery mildew, pod and stem blight and anthracnose, can sneak in to the Midwest. But University of Kentucky plant pathologist Don Hershman says that while there are exceptions, most of these diseases develop too late in the season to cause measurable yield loss from Kentucky north. Other diseases—such as charcoal rot, soybean cyst nematode, sudden death syndrome and Phytophthora root and stem rot—and viruses are more common, but they are not impacted by foliar fungicides.
"Without disease control being needed, benefits are not predictable and results can and do vary considerably,” Hershman says. "I don't think anyone can predict a pure ‘plant health' response divorced from disease control.”
Here's the rub. There's disagreement among researchers, university Extension specialists, growers and industry on fungicide use. Pesticide applications made in the absence of a specific target pest are contrary to integrated pest management principles. There is already some evidence that indiscriminate use of fungicides has resulted in increased insect and mite activity because native fungi are suppressed.
Still, fungicide use in soybeans dramatically increased, especially in 2008. "Use of Headline [pyraclostrobin] doubled this past year—from 3 million acres to 6 million acres,” says Gary Schmitz, BASF Corporation Midwest technical manager.
"We're still tallying yield studies, but on average, it appears growers realized a 4 bu. to 8 bu. increase,” Schmitz says.
- December 2008