Strobilurin Resistance

 Reporting on some of his research while employed 
 by the University of Illinois, Dr. Carl Bradley, extension plant 
 pathologist at the University of Kentucky, discussed disease
 management of field crops.

 Photo by John LaRose, Jr.

Use Several Methods, Modes Of Action To Curb Resistance

MidAmerica Farmer Grower

   Strains of the frogeye leaf spot pathogen of soybean, known as Cercospora sojina, have been shown to be resistant to strobilurin fungicides, and Dr. Carl Bradley, extension plant pathologist at the University of Kentucky, reported recently on some of his research on that while employed by the University of Illinois. Disease management of field crops such as corn, soybean and wheat is his specialty.
   “Back in 2010, I had a project that was funded by the Illinois Soybean Association where we were evaluating strains of the frogeye leaf spot pathogen for resistance to strobilurin fungicides,” he said. “At that time, we began to find resistant strains in western Kentucky, southern Illinois and western Tennessee. After that, the United Soybean Board began to fund that project and we then found strains across several different states.”
   Now, strobilurin resistant strains have been documented just about wherever soybeans are grown in the midsouth and part of the midwest. Bradley discussed the management of strobilurin resistant strains.
   “We’ve conducted research looking at different chemistry classes and their ability to control frogeye leaf spot caused by these strobilurin resistant strains, and we have found that other chemistries do work, so that’s really good news,” he said.
   “Also, there’s another soybean pathogen known as Septoria glycines that causes Septoria Brown Spot, and we now have actually identified strains of that pathogen that also are resistant to strobilurin fungicides in Illinois, so there’s some bad news there as well,” he added.
   Bradley said farmers now need to focus on diseases through other methods in addition to fungicides.
   “Think about how resistant your soybean varieties or corn hybrids might be to certain diseases,” he suggested. “If you have problems with those diseases year in and year out, you really need to be using resistant varieties. Also think about crop rotation as another method of control. Then, fungicides certainly can be one of those tools to help you control these diseases, but it doesn’t have to be the only one. We really need to be focusing on all of the disease management tools.”
   He urged farmers to consider their disease risk, how susceptible the variety or hybrid might be, and scout for diseases.
   “If you don’t see anything out there, then you probably don’t need a foliar fungicide, so just hold those fungicides for disease control and not for other purposes,” he suggested. “Also, when you do apply a fungicide, think about using products that contain multiple chemistry classes, which many products today contain different active ingredients from different modes of action. Those are all important things to consider for managing fungicide resistance.
   “We can’t prevent fungicide resistance  from happening, but we can certainly slow it down, if we use these fungicides prudently and use them along with other management tools for disease control,” he added. “Then when you use fungicides, be sure to use different modes of action.” ∆
   BETTY VALLE GEGG-NAEGER: Senior Staff Writer, MidAmerica Farmer Grower

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