Comparison of two disease assessment methods for assessing Cercospora leaf spot in sugar beet

Abstract Two disease severity scales for Cercospora leaf spot (CLS) assessment were compared. CLS was assessed in two experimental fields in the Netherlands in 1999 using two scales: a single leaf severity assessment, as used in the IPS-system (Integriertes Pflanzenschutzsystem) in Germany, referred to as DS IPS , and a whole plant assessment, Agronomica diagram from Italy, referred to as DS AGR . To obtain a range of disease severities, fungicides were applied at defined action thresholds based on disease incidence and severity. There was an exponential relationship between DS IPS and DS AGR ( R 2 =86%) for pooled data with little change in the whole plant assessment above DS IPS =5%. An exponential curve best fitted DS IPS and root and sugar weight in fields severely infected with CLS, whereas a linear curve was found for mildly infected fields. A linear curve fitted DS AGR best with root and sugar weight in both severely and mildly infected fields. No relationship was found between both DS IPS and DS AGR and sugar content. The use of DS AGR was less time consuming in monitoring and was done with greater accuracy, efficiency and level of reproducibility than DS IPS . These results demonstrate that CLS assessment can be less time-consuming and more practical in application.