Sensitivity of Coniella diplodiella to pyraclostrobin in Jiaodong Area and comparison with four other fungicides

The sensitivities of 52 strains of grape white rot pathogen (Coniella diplodiella) from Jiaodong area of Shandong Province to pyrazolone were determined by the mycelial growth rate method, and the effect of salicyloxime acid (SHAM) on the mycelial growth of grape white rot pathogen and its sensitivity to pyraclostrobin were tested. Laboratory toxicities and field experiments were also carried out to compare the sensitivity of pyraclostrobin with four other fungicides with different mechanisms. The sensitivity of C. diplodiella to pyraclostrobin with the addition of SHAM (20 μg/mL) was significantly increased (F = 5.5017, P = 0.0388). The virulence of pyraclostrobin to grape white rot was 1.17 times higher than that by using pyraclostrobin alone. Moreover, these tested isolates were highly sensitive to pyraclostrobin. Their EC₅₀ to pyraclostrobin were in the range of 0.176-6.012 μg/mL, with the mean value of 2.826 μg/mL. The frequency curve of pyraclostrobin was continuous and unimodal, and followed the normal distribution. Hence, the mean EC₅₀ of 2.826 μg/mL could be served as the baseline sensitivity of C. diplodiella to pyraclostrobin in Jiaodong. The values of EC₅₀ of tebuconazole, thiram, mancozeb and carbendazol were 0.364-16.873, 5.236-25.562, 15.912-84.778 and 1.819-568.690 μg/mL, respectively. Besides, the sensitivity of C. diplodiella to pyraclostrobin was similar to the sensitivity to tebuconazole, which was significantly higher than that of other three fungicides, including thiram, mancozeb and carbendazim. These results have provided a theoretical basis for selection and rational rotation of grape white rot disease in the field.