Submitted to: Sugarbeet Research and Extension Reports
Publication Type: Proceedings
Publication Acceptance Date: 2/28/2001
Publication Date: N/A
Interpretive Summary: Cercospora leaf spot is the most serious leaf disease of sugarbeet in the north Great Plains of the U.S.. Foliar fungicides are the principle means of controlling the disease, which is caused by the fungus Cercospora beticola. In the past two decades, increases in the fungus population of members that are gaining resistance to the fungicides used have been documented by our lab. Increased tolerance to the common fungicides triphenyltin hydroxide, mancozeb, and thiophanate methyl have been observed for several years running. It is important to continue monitoring fungicide resistance in this fungus, in order to determine if sugarbeet growers are indeed getting economic return through application of the fungicide. In 2000, testing for resistance to tetraconazole, a new fungicide being used in the Red River Valley, was begun. Low level resistance to this fungicide was documented fot the first time in Cercospora isolates obtained in Minnesota and North Dakota. Our USDA- Fargo remains the only lab in the nation to provide this analysis of fungicide tolerance to US sugarbeet growers.
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. EminentTM (tetraconazole) has been used on sugarbeet in Minnesota and North Dakota only in the past few years; preliminary testing for tolerance to this fungicide is presented in this year's study. 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 now includes surveying for tolerance to mancozeb. Testing for baseline tolerance to tetraconazole is also beginning this year, as this represents new chemistry available to the grower for the control of leaf spot disease. The results of the study found similar presence of fungicide resistant C. beticola isolates to previous years.