COLUMBIA, Mo. – Fungicides can be an essential part of an integrated pest management plan, but they do not always provide a positive return on investment for soybean producers, according to University of Missouri strip trial research.

Missouri farmers apply fungicides to about 65% of soybean acres, says MU Extension state plant pathologist Mandy Bish, yet only 10% of fields are scouted to determine need before fungicides are applied. In 2004, before soybean rust entered the United States, fungicides were applied to only 1% of Missouri soybean fields.

MU Extension strip trials on soybean fields across the state have shown that many fungicide applications result in yield increases, but those increases do not always offset the cost of a $40 per acre application.

In 66 strip trials, only 21% showed yield increases greater than or equal to 3.3 bushels per acre following an R3 fungicide application, says Bish. In 23% of the trials, yield was lower following a fungicide application. Researchers in nine Midwestern states and Canada found similar results, noting a 2.7% yield increase in fungicide-treated soybean compared to untreated soybean.

“In a year where we are looking to cut back on inputs, fungicide applications to soybean may be one practice that farmers want to reevaluate,” Bish says. “We do not often see foliar disease outbreaks in Missouri soybean fields to levels that warrant a fungicide application.”

In addition to the financial burden, overuse of fungicides poses the risk of fungi developing resistance over the long haul. “We know that we have fungicide resistance occurring with the fungus that causes frogeye leaf spot disease in Missouri soybeans,” she says.

The Crop Protection Network says there are times when spraying fungicides proves effective. Diseases such as soybean rust, white mold, target spot and severe outbreaks of frogeye leaf spot and septoria brown spot can warrant fungicide applications. Timing of the application depends on the disease.

Genetics and best management practices remain the best way to control most foliar diseases of soybean in Missouri, says Bish.

For more information on MU Extension soybean R3 fungicide trials, go to http://muext.us/SR3FT.

Missouri Soybean Merchandising Council, Missouri Corn Merchandising Council, Missouri Fertilizer Control Board, North Central Sustainable Agriculture Research and Education partnerships, and MU Extension fund MU Extension Strip Trial Program research.