Cercospora leaf spot in sugar beet. Epidemiology, life cycle components and disease management

Cercospora beticola, the causal agent of Cercospora 1eaf spot (CLS) in sugar beet, causes I reductions in sugar yield and financial returns. Section I describes the epidemiology of CLS. Two disease severity indices were compared and their relation with sugar yield modelled. A linear curve fitted the Agronomica disease severity index with sugar yield in both severely and mildIy infected fields, whereas for a 1eaf disease severity assessment this relationship was exponential and linear, respectively. The Agronomica disease severity index was less laborious and improved disease assessment. Using spatial and temporal rnodels, the within-row dependencies of CLS disease severities was demonstrated. However, disease increase on a given plant was largely determined b>disease on that plant. Similarly when describing the within-plant dynamics of disease, i1 was concluded that the major determinant of disease increase on a given 1eaf layer on ? plant was from disease on that 1eaf layer. Spraying a fungicide twice changed the contribution of the lower 1eaf layers. In one mildly infected field, these 1eaf layers were more often significant in the model; in the other severely infected field less often. Ir section II studies on the life cycle of CLS are reported. It was demonstrated that C beticola is able to infect sugar beet through the root in glasshouse, climate room, and ir field experiments. The genetic variability of C. beticola was studied in an international collection of isolates. Between and within geographic regions, genetic variability is high A C. beticola specific PCR primer was developed, which enabled detection of C. beticolc in plant tissue, We showed systemic growth of C. beticola in a sugar beet seedling after root infection. Section III describes the development of a supervised control system. The use of an action threshold involving two early sprays and weather-based treatment: resulted in sugar yields and financial returns similar to calendar sprayed treatments, am saved up to two fungicide applications.