Poster Session: Disease Control and Pest Management - Cultural Control

233-P

Foliar applications of iron suppress Cercospora leaf blight and increases yield in soybean.
E. C. SILVA (1), A. K. Chanda (1), T. G. Aroca (1), C. L. Robertson (1), B. M. Ward (1), R. W. Schneider (2)
(1) Louisiana State Univ, Agricultural Center, Baton Rouge, LA, U.S.A.; (2) Louisiana State university., Baton rouge, LA, U.S.A.

Cercospora leaf blight (CLB) caused in soybean by Cercospora kikuchii is a devastating disease. Losses in Louisiana fields can range from 20% to complete crop failure. Preliminary work testing foliar applications of reagent grade micronutrients showed that Fe decreased CLB severity. The objective of this work was to test the effects commercial formulations of Fe, Manny Plex Fe and Fe EDTA (Brandt Consolidated, Springfield, IL) on leaf colonization by C. kikuchii, symptom development (blight and purple leaves), and yield. Four rates of each formulation were applied to field plots at the R3 and R5 growth stages. Leaf tissue analyses for microelements and qPCR testing for the pathogen were performed. Disease severity was assessed quantitatively for leaf blight and purple leaf symptoms, and yield was measured. Results showed there was no correlation between leaf colonization and symptoms (neither purple nor blight). In addition, Fe concentration in leaves did not affect biomass of C. kikuchii. Purple leaf symptoms increased in severity as Fe concentration in leaves increased, but severity decreased as Fe concentrations surpassed 200 ppm. Blight symptoms were completely suppressed above the threshold of 280 ppm. There was no correlation between purple leaf and blight symptoms. There was a positive relationship between concentrations of Fe in leaves and yield and negative relationships between yield and Cercospora biomass and severity of blight and purple leaf symptoms.