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Poster: Biology & Disease Mgmt: Chemical Control


Managing QoI-resistant Cercospora sojina in Mississippi soybean and assessing the physiological impacts of foliar fungicide phytotoxicity
J. MANSOUR (1), M. Tomaso-Peterson (2), A. Henn (2), J. Bond (1), T. Irby (2) (1) Mississippi State University, U.S.A.; (2) Mississippi State University, U.S.A.

Following the widespread detection of quinone outside inhibitor (QoI) resistant frogeye leaf spot (FLS) (Cercospora sojina Hara) in Mississippi during 2013 and 2014, effective management of FLS in susceptible cultivars requires the use of fungicide products that contain alternative, non-QoI, modes of action (MOA). One drawback to applying alternative MOAs, such as demethylation inhibitors (DMI), can be phytotoxicity on treated soybean leaves. Field trials were conducted in 2015 to assess fungicide efficacy on QoI-resistant FLS severity and the resulting phytotoxicity on several soybean cultivars with differing FLS reactions. The fungicides chosen have previously been observed to produce moderate to severe phytotoxicity. Six different fungicide products, comprised of single or multiple MOAs, were applied at R2, R3, and R4 along with a non-treated. FLS and phytotoxicity were visually assessed pre- and several times post-application. Plant height, number of pods and nodes were recorded to determine physiological impacts. Analyzed data revealed that certain MOAs significantly reduced FLS severity compared to the non-treated. In addition, prothioconazole resulted in significantly greater phytotoxicity than the non-treated, a difference of 29.4%. However, yield was not significantly reduced as a result of fungicide phytotoxicity. In addition, plant heights and number of nodes per plant were not significantly different between fungicide treatments and the non-treated.