Toxicity of several fungicides against Corynespora cassiicola and the field efficacy in the control of kiwifruit brown spot

Abstract: 【Objective】The study aimed to screen out effective fungicide for controlling kiwifruit brown spot disease.【Methods】The toxicity of nine primary chemical fungicides against Corynespora cassiicola were measured by mycelial growth rate and conidial germination inhibition methods. The compound fungicides were selected according to the toxicity of different fungicides to determine the toxicity to mycelia and field control efficacy.【Results】The toxicity of tebuconazole, pyraclostrobin and difenoconazole to the mycelial growth of C. cassiicola was the highest, and their EC50 values were 10.81, 11.69 and 12.48 µg ·mL- 1 , respectively. The carbendazim and pyraclostrobin had low toxicity to mycelial growth, and their EC50 values were 35.19 and 41.85 µg·mL-1 , respectively. The toxicity of tebuconazole and trifloxystrobin to conidial germination was the highest, and their EC50 values were 8.33 and 8.50 µg · mL- 1 , respectively. The toxicity of difenoconazole, azoxystrobin and pyraclostrobin was medium, with the EC50 values of 12.69, 14.60, and 15.89 µg ·mL-1 , respectively. The toxicity of carbendazim and boscalid was lower, with the EC50 values of 33.65 and 40.35 µg·mL-1 , respectively. Based on the results of these primary chemical fugicides, as well as the field investigation on fungicides using, we selected some primary fugicides with better inhibitory effects on C. cassiicola in the laboratory, and chose the compound fungicides containing these primary fugicides as the test agents. Among the eightcompound fungicides, the toxicity of fluzoxammide-pyraclostrobin to the mycelial growth of C. cassiicola was the highest. When the concentration was 1 µg·mL-1 , fluzoxammide-pyraclostrobin had the best inhibitory effect, but only reached 63.45%, and the others were all lower than 50%. When the concentration was 10 µg · mL- 1 , the inhibitory effect of fluzoxammide-pyraclostrobin on mycelium was still the highest, and the inhibitory rate reached 88.59%. The inhibitory effects of the difenoconazole-trifloxystrobin and fluriramide-trifloxystrobin were the second, with inhibition rates of 77.30% and 73.08%, respectively. The inhibitory effect of the tebuconazole · trifloxystrobin was the worst, and the inhibitory rate was only 39.44% . The fluzoxammide- pyraclostrobin could completely inhibit mycelium growth when the inhibition rate of fluriramide-trifloxystrobin was 85.85%, but the inhibitory effect of the tebuconazole · trifloxystrobin was the worst, and the inhibitory rate was 46.93% at the concentration of 20 µg · mL- 1 . When the concentration was 50 µg · mL- 1 , the inhibitory effect of the fluriramide-trifloxystrobin and propiconazole·azoxystrobin was 96.08% and 91.46%, respectively, while the fluzoxammidepyraclostrobin could completely inhibit mycelium growth. In addition, the inhibitory effect of the difenoconazole-trifloxystrobin reached 89.55%; The inhibitory effect of the tebuconazole ·trifloxystrobin was still the worst, and the inhibitory rate was only 51.92%. The fluriramide-trifloxystrobin could completely inhibit mycelium growth at the concentration of 100 µg · mL- 1 . And the inhibition rates of the propiconazole- azoxystrobin, difenoconazole- trifloxystrobin, difenoconazole- azoxystrobin, clofiurfenazole-pyraclostrobin and tebuconazole-trifloxystrobin to the mycelial growth were 99.46%, 95.04%, 89.04%, 60.03% and 57.18%, respectively. According to the inhibition effects of 7 compound fungicides on mycelium growth of C. cassiicola and their field effects, 6 agents of fluzoxammide-pyraclostrobin, fluriramide- trifloxystrobin, difenoconazole- trifloxystrobin, difenoconazole- azoxystrobin, clofiurfenazole-pyraclostrobin and tebuconazole-trifloxystrobin were selected for field efficacy control tests. In the field efficacy test, after 7 days of the first application, the control effect of each compound fungicide on kiwifruit brown spot disease was different. Among them, the control effect of the fluzoxammidepyraclostrobin was up to 76.17%, and the control effects of the difenoconazole-azoxystrobin, clofiurfenazole- pyraclostrobin were over 60%. The control effects of the tebuconazole-trifloxystrobin and difenoconazole-trifloxystrobin were 58.60% and 53.50%, respectively. 7 days after the third application, the control effect of fluzoxammide-pyraclostrobin was up to 85.69%, and the control effects of the fluriramide-trifloxystrobin and difenoconazole-azoxystrobin were up to 83.25% and 81.33%, respectively. And the control effects of the other three compound fungicides did not exceed 80%. Among them, the control effect of the difenoconazole-trifloxystrobin was only 70.19%. According to the control effects 7 days after the first application and 7 days after the third application, the fluzoxammide-pyraclostrobin had the best effect, followed by the fluriramide-trifloxystrobin. According to the field efficacy test, two kinds of compouond fungicides, the fluzoxammide-pyraclostrobin and fluriramide-trifloxystrobin, were promoted to use for controlling kiwifruit brown spot disease in Dujiangyan and other planting areas in Sichuan Province. From 2019 to 2021, the control effect of the two compound fungicides on kiwifruit brown spot in different planting areas could reach more than 80.00%. In 2019, the control effect of the orchards in 5 planting areas, including Lushan and Dujiangyan, was 81.45%-89.25%, and the incidence rate in the treatment group was basically controlled within 50%, among them the incidence rate in Mianzhu and Lushan was only 8.86% and 12.40% respectively. In 2020, the disease control effect of the orchards in Anzhou, Lushan and Dujiangyan planting areas reached 86.79%, 86.61% and 84.87%, respectively. The disease control effect of Anzhou and Dujiangyan orchards in 2021 was 81.03% and 81.16%, respectively. According to the disease index and incidence of the disease in different planting areasfrom 2019 to 2021, the disease had a trend of increasing year by year. But the control effect of the set of fungicides application scheme for the disease could still remain above 80.00%.【Conclusion】The fluriramide-trifloxystrobin and difenoconazole-azoxystrobin should be recommended for the prevention and control of kiwifruit brown spot disease.