Variety resistance to Cercospora leaf spot and fungicide application as tools of integrated pest management in sugar beet cultivation – A German case study

Abstract

Variety resistance is a principal element of integrated pest management and part of the integrated control of Cercospora leaf spot (CLS) in sugar beet. Currently, varieties with a high level of resistance to CLS yield lower than susceptible ones and consequently lack acceptance in commercial farming in Germany. In a comparative analysis of three different trial series, yield performance of selected sugar beet varieties with varying susceptibility to CLS was examined with regard to CLS-disease severity of the trial site. In disease-free environments, the current resistant varieties yielded 5–7% less than susceptible varieties, indicating progress in sugar beet breeding and a reduction in yield-penalty by half within the last 20 years. In environments with strong infestation, the resistant variety achieved a white sugar yield (WSY) comparable to varieties with generally higher yield potential. The observed changes in variety-ranking, especially between environments with low to medium and strong CLS-infestation, suggested that superiority of some varieties depended on disease pressure in the respective growing area. It is concluded that disease severity of CLS should be taken into account for the characterisation of varieties in order to improve variety-recommendations and to allow conclusions about the superiority of varieties in regions with varying disease pressure.An analysis of the effect of different control strategies agreed with prior studies that WSY is higher in treatments with fungicide applications according to the summary threshold system than in the non-treated control. Preventive fungicide applications appeared to be unnecessary for German growing areas as they did not increase WSY. Moreover, a reduced strategy related to the summary threshold system may allow a reduction in fungicide use as it achieved a WSY comparable to the threshold strategy but with omission of the last application.