The University of Illinois and University of Tennessee have conducted research confirming resistance of frogeye leaf spot to strobilurin fungicides in a Tennessee soybean field. The Fungicide Resistance Action Committee has determined that strobilurin fungicides have a high risk for fungal pathogens developing resistance to them.
"Plant pathogenic fungi developing resistance to strobilurin fungicides is not new," said University of Illinois Extension Plant Pathologist Carl Bradley. "This has already occurred in potatoes and other crop and disease systems where multiple fungicide applications occur during the growing season."
However Bradley says they were surprised to find resistance so soon, as soybean fields are usually only treated once a season if at all.
The U of I research to develop a fungicide resistance monitoring program began in 2008 with funding from the Illinois Soybean Association. During that time samples and testing were conducted on plants collected in Illinois.
"This year, we decided to cast our net a little farther, particularly in the South," Bradley said. "In Tennessee, FLS is a major soybean foliar disease. Dr. Melvin Newman of the University of Tennessee sent me samples from a field that had been sprayed twice with strobilurin fungicides but still continued to have high levels of FLS, which was an indication of potential fungicide resistance."
Currently Tennessee is the only state where this has been documented but testing in several states continues. The Illinois Soybean Association will continue funding the project in 2011 and Bradley's team is also expanding the research to look at possible resistant gray leaf spot and northern corn leaf blight resistance in corn fields.
For more information check out The Bulletin, an online publication written by U of I Extension specialists in crop science, at ipm.illinois.edu/bulletin/.