Effect of fungicide strategy and variety on Cercospora leaf spot epidemics in sugar beet

Cercospora leaf spot disease is becoming increasingly important in Germany. At the same time, existing fungicides are losing efficacy. Therefore, efficient control strategies have to be developed to stabilize yields and reduce the further spread of resistance. In 2017 and 2018, eight field trials were conducted to test the efficacy of four fungicide strategies against Cercospora in a susceptible and a tolerant sugar beet variety. All fungicide strategies reduced infestation in all environments. With moderate infestation, this reduction did not always affect yield, especially in the tolerant variety. Furthermore, the tolerant variety reached the threshold for the second or third fungicide application up to three weeks later than the susceptible one. In the case of strong to extreme infestation, the fungicide strategies including a contact fungicide in addition to triazoles and thiophanate-methyl had the greatest effect on infestation and white sugar yield. Tolerant varieties and also contact fungicides, which are only approved for emergency situations, can currently contribute to the resistance management of Cercospora beticola.