Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Proceedings
Publication Acceptance Date: 1/13/1998
Publication Date: N/A
Interpretive Summary: Fungicides are important to sugarbeet growers in order to prevent loss to the crop from fungal diseases. Cercospora leaf spot is serious disease in sugarbeet and is caused by a fungus that infects the leaves of the beet plant. After years of using fungicides to try to control Cercospora leaf spot, some fields are showing Cercospora fungus that is becoming tolerant to the fungicide. The result is that application of fungicide is no longer as effective at preventing the disease as previously. No all fields show this effect of fungicide tolerance. Thus, continued monitoring of the Cercospora fungus in the field is important in order to keep records of the level of fungicide tolerance in this fungus.
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 out 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.