Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Proceedings
Publication Acceptance Date: 3/9/1999
Publication Date: N/A
Interpretive Summary: Sugarbeet growers send considerable financial resources in the chemical control of leaf spot disease caused by the fungus Cercospora beticola. In recent years, the fungus has been developing the ability to resist or tolerate the fungicides that are applied to control the disease. The percent of the fungus population in the field that has fungicide tolerance is of importance to sugarbeet growers, since it can determine to what extent they will apply additional fungicide in efforts to save the crop. Data from the presented research indicates that fungicide tolerance is increasing incrementally in sugarbeet fields of North Dakota and Minnesota. This warrants further monitoring in future years.
Technical Abstract: Triphenyltin hydroxide (TPTH) has been used extensively in the Northern Great Plains in recent years for the control of Cercospora leaf spot on sugarbeet. Although mancozeb and, to a lesser extent, the benzimidazole fungicides often are implemented in conjunction with TPTH for optimum leaf spot control, TPTH continues to be the most widely used compound for control of the disease. Testing in our USDA-ARS Fargo laboratory of Cercospora that was isolated from leaf spot in the sugarbeet fields in North Dakota and Minnesota for the tolerance or resistance to fungicides first revealed tolerance to TPTH in 1994. The testing program has continued to the present and includes, for the first time, extensive surveying for tolerance to mancozeb. As in previous years, fields in the southern Minnesota growing region and in all factory districts from Wahpeton to Drayton in the Red River Valley were surveyed. Samples were tested for resistance to thiophanate methyl (TM; a benzimidazole fungicide) and for tolerance to TPTH and mancozeb at two different exposure levels.