Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Abstract Only
Publication Acceptance Date: 2/8/1999
Publication Date: N/A
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.