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Effects of Herbicides on Sclerotinia Crown and Stem Rot of Alfalfa

July 1997 , Volume 81 , Number  7
Pages  787 - 790

S. L. Reichard , Graduate Research Assistant , R. M. Sulc , Assistant Professor, Department of Horticulture and Crop Science , L. H. Rhodes , Associate Professor, Department of Plant Pathology , and M. M. Loux , Associate Professor, Department of Horticulture and Crop Science, The Ohio State University, Columbus 43210



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Accepted for publication 31 March 1997.
ABSTRACT

This study was conducted to determine whether herbicides and adjuvants registered for poste-mergence use in alfalfa have an effect on Sclerotinia crown and stem rot (SCSR). In a controlled environment, disease severity index (DSI) of alfalfa seedlings was reduced by pronamide and 2,4-DB compared with the untreated control, whereas bromoxynil and 13% sethoxydim + petroleum-based adjuvant (PBA) increased DSI. In the field, disease severity in all herbicide treatments was similar to that in untreated alfalfa. In a second controlled-environment study, pronamide and 2,4-DB reduced DSI compared with the no herbicide control when seedlings were inoculated 1 day after herbicide application, but this protective effect was not observed when seedlings were inoculated 8 days or longer after herbicide application. The results demonstrate that several herbicides are capable of suppressing or enhancing SCSR severity in a controlled environment if seedling inoculation occurs soon after herbicide application; however, the residual effect of these herbicides on SCSR appeared to be much shorter than the 4- to 6-week infection period occurring in the field.


Additional keywords: Medicago sativa, Sclerotinia trifoliorum

© 1997 The American Phytopathological Society