If he had to choose a plant pathogen to develop resistance to strobilurin fungicides, Carl Bradley says the frogeye leaf spot fungus would have been one of his top choices.
First off, the University of Illinois plant pathologist notes the disease doesn't travel very far. Unlike soybean rust, it tends to remain in a localized area.
"The other good news is there are soybean varieties available that are resistant to frogeye leaf spot," Bradley adds.
Still, that doesn't change the fact that strobilurin-resistant strains of the frogeye leaf spot fungus, Cercospora sojina, have been confirmed in five states: Illinois, Kentucky, Missouri, Tennessee and Louisiana. In Illinois, resistant strains were found in Gallatin and Pope Counties in both 2010 and 2011. The first instance of strobilurin resistant frogeye leaf spot was found in Tennessee in 2010.
With its mode of action targeting a single site, Bradley says scientists have known for a while that there is a high risk of selecting for stobilurin-resistant strains of fungi.
Frogeye leaf spot typically is not a significant threat for most of Illinois. Still, Bradley says farmers need to be proactive in deploying practices that slow down fungicide resistance development in other pathogens of soybean and corn.