Effect of glyphosate on Cercospora beticola on glyphosate-resistant sugar beet.

In Minnesota and North Dakota, Cercospora leaf spot (CLS), caused by the fungus Cercospora beticola Sacc., is the most damaging foliar disease of sugar beet (Beta vulgaris L.). Fungicide applications are necessary under moderate to severe disease pressure to control CLS to obtain economically viable yields of recoverable sucrose. Field trials were conducted near Foxhome, Minnesota in 2005 and 2006 to determine whether the broad-spectrum herbicide glyphosate applied post inoculation to glyphosate-resistant sugar beet controls C. beticola and improves crop yield and quality compared to using fungicides. The research site was artificially inoculated with C. beticola and multiple applications of glyphosate were applied alongside the fungicides tetraconazole, pyraclostrobin, and triphenyltin hydroxide used in rotation. CLS disease severity was high in both years as measured by the area under the disease progress curve (AUDPC). Glyphosate applied post inoculation at the same time as parallel applications of fungicides were performed did not provide effective control of CLS and resulted in similar AUDPC, yield and quality as the non-treated check. Fungicides provided effective control of C. beticola with lower AUDPC and resulted in significantly higher yields and recoverable sucrose than the non-treated check. Additional