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Fungus rebounds after fungicide application


Lauren Quinn University of Illinois
URBANA, Ill. – Septoria brown spot may be considered the “common cold” of soybean diseases, but that doesn’t mean it’s entirely benign. The fungal disease can cause 10 percent to 27 percent yield loss. Many farmers fight it by using fungicide, but a new University of Illinois study shows Septoria can actually increase after fungicide application.

“When we applied the fungicide, most of the fungi on plant surfaces decreased,” said Santiago Mideros, an assistant professor in the department of crop sciences at the University of Illinois and co-author of the study. “But a few of the fungi increased, Septoria among them. It was very surprising.”

Led by Heng-An Lin, a former crop-sciences doctoral student, the study was designed to identify and track the soybean mycobiome – the collection of fungi living on soybean plants – in field conditions.

Lin and Mideros inoculated half the soybean seedlings in their field trials with Septoria. Then using genetic information and bioinformatics analyses, they identified fungal species on leaves throughout the season before and after applying fungicide.

“We chose a mixture of fluxapyroxad and pyraclostrobin fungicides because it's quite commonly used in the Midwest,” Mideros said. 

The fungicide controlled many fungi, but not Septoria. It removed Septoria’s competitors, allowing the pathogen to flourish, Mideros suggested. The result calls into question the common practice of yield-protective fungicide application.

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