The last few years, frogeye leafspot has been the Number One topic for telephone calls Tom Allen has received in Mississippi.
“Through the soybean rust monitoring network, we were able to collect a lot of frogeye leafspot-infected leaf samples,” said the Mississippi State University plant pathologist at the recent Tri-State Soybean Meeting. “At first, we were sending some of those (for testing) to Carl Bradley at the University of Illinois. I stopped that years ago for two reasons. One, the mail service became unreliable and, two, overnighting leaf samples to Illinois cost $76 per envelope.”
Allen and colleagues implemented their own project that the Mississippi Soybean Promotion Board “graciously funded to support a graduate student. We collected an extremely large number of samples throughout Mississippi during 2013 and 2014. As a result of the survey, and the graduate student’s research, we were able to determine that approximately 96 percent of the fungal isolates collected — with more than 600 total isolates collected throughout the state — were resistant to the strobilurin chemistry.”
Following the results of the two years of research, Allen said, “It is pretty safe to say if you have frogeye leafspot in Mississippi on a susceptible variety, the fungus is resistant to strobilurin fungicides. In the future, a dual mode of action, or mixed mode of action fungicide, that contains a curative compound such as a triazole will be necessary to manage frogeye leaf spot.”
Allen warned attendees when selecting soybean varieties “do not choose the most frogeye leafspot-susceptible. And if you do happen to choose a frogeye leafspot-susceptible variety, do not pre-book a standalone strobilurin fungicide. It won’t be very beneficial. Choose a fungicide product that will be beneficial for the specific varieties grown on your farm.”