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Poster: Biology & Disease Mgmt: Integrated Pest Mgmt


Correlating the Effects of Glyphosate on Soybean Nutrition with Cercospora Leaf Blight and Septoria Brown Spot
T. GARCIA AROCA (1), E. Silva (1), B. Ward (1), C. Robertson (1), P. Price (1), R. Schneider (1), R. Levy (2) (1) Louisiana State University, Baton Rouge, LA, U.S.A.; (2) Louisiana State University, Alexandria, LA, U.S.A.

Glyphosate is linked to detrimental effects on soil microbiota and reduced levels of metal cations available for plant uptake. There is no agreement in literature regarding effects of glyphosate on plant diseases or micronutrient uptake. Some authors claim the use of glyphosate in Roundup Ready (glyphosate-resistant) soybeans leads to increased disease severity due to negative effects on uptake of manganese (Mn), iron (Fe) and other micronutrients, while others dispute these findings. This controversy is relevant to findings made by our laboratory regarding tissue concentrations of certain micronutrients, e.g. Mn and Fe, which substantially affect Cercospora leaf blight (CLB) in soybean. Therefore, we tested the hypothesis that glyphosate is affecting disease severity in soybean. Twelve Roundup Ready soybean varieties were planted at two locations in Louisiana in randomized complete block designs. Plots were either not sprayed or sprayed with Roundup. CLB and Septoria brown spot disease assessments were conducted in 2014 and 2015. Samples were taken for micronutrient analyses and real-time quantitative PCR (qPCR) for the CLB pathogen. Results showed significant increases of some elements, e. g. N and Mn, for Roundup-treated samples. CLB and Septoria brown spot severities were higher in non-treated plots. Results from qPCR analyses indicated more pathogen DNA (biomass) in Roundup-treated samples, however, these findings were not correlated with disease severity.