Improved integrated management of Cercospora leaf spot (Cercospora beticola) with a new-type resistant sugar beet (Beta vulgaris L.) variety

Abstract Plant breeding has continued to improve the resistance of sugar beet to Cercospora leaf spot (CLS) caused by the fungus Cercospora beticola. A new, highly resistant variety type has recently been introduced, which we tested in a three-year field trial series in a wide range of environmental conditions across Germany and Austria. Compared with a standard variety, the epidemic progression of CLS was significantly reduced. In the standard variety, CLS incidence reached the threshold for fungicide application in all 25 field trials and 1–4 fungicide applications were necessary. In the highly resistant variety, CLS never reached the treatment threshold in twelve trials. In the other 13 trials, 1–2 fungicide applications were made according to the threshold system. A close linear relationship was found between CLS severity at harvest and white sugar yield loss. Depending on the disease pressure of CLS, yield loss without fungicide reached up to 30% for the standard variety and up to 12% for the highly resistant variety. Our study shows that highly resistant varieties improve the integrated management of CLS by reducing the use of fungicides without sacrificing yield. However, a balance must be struck between the aim to reduce fungicide use and preventing the development of resistance-breaking strains of the fungus. It is therefore recommended that new-type resistant varieties are treated with fungicides according to approved integrated management programmes to prevent severe disease progression.