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Effect of glyphosate application on sudden death syndrome of soybean under different field conditions
Y. R. KANDEL (1), C. A. Bradley (2), K. A. Wise (3), M. Chilvers (4), A. Tenuta (5), V. M. Davis (6), P. Esker (6), D. L. Smith (6), D. Mueller (7). (1) Iowa State University, Ames , IA, U.S.A.; (2) University of Illinois, Urbana, IL, U.S.A.; (3) Purdue University, West Lafayette, IN, U.S.A.; (4) Michigan State University, East Lansing , MI, U.S.A.; (5) Ontario Ministry of Agriculture and Food, Guelph

Sudden death syndrome (SDS), caused by <i>Fusarium virguliforme</i>, is an important yield limiting disease of soybean. Glyphosate has been used for many years to control weeds in glyphosate-tolerant soybean. The effect of glyphosate application on SDS is not clearly understood. The objective of this study was to examine how glyphosate use affected SDS severity under field conditions. Fifteen field experiments were conducted in IA, IL, IN, MI, WI, and Ontario, CAN during 2011, 2012, and 2013. Six treatment combinations of non-glyphosate herbicides and glyphosate including pre- and post-emergence, single and multiple applications were compared. Disease severity was significantly different (<i>P</i><0.05) across the location-years. Mean foliar disease index (FDX) ranged from 0 to 65% across field trials. Highest disease was noted in irrigated plots. There were no statistically significant effects of herbicide treatments or interactions (<i>P</i>>0.05) on disease severity. The mean FDX among the treatments ranged from 10 to 14%. These results indicate that the environment, particularly soil moisture, played a significant role on SDS development. Glyphosate-treated plots did not have more SDS than plots with other herbicides. Glyphosate-treated plots tended to yield more than plots treated with other herbicides. This fifteen location-year study demonstrated that glyphosate application does not increase SDS severity or adversely affect soybean yield under field conditions.

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