Study on the chemical control of hypertrophic sorosis scleroteniosis disease in mulberry

Abstract:【Objective】The hypertrophic sorosis scleroteniosis caused by Ciboria shiraiana is a destructive disease in mulberry production. Carbendazim and thiophanate-methyl are currently being used as the main fungicides to control the disease, which have caused severe impacts on environmental pollution and food safety. To safely and effectively control the disease, high-efficiency fungicides were selected by mycelium growth rate method and used for field trial in 2019 and 2021. The high efficiency and safe fungicide screened from 2019 field experiment was used for study on the efficacy of controlling the disease at different stages, and the two common biological fungicides Trichoderma harzianum and Bacillus subtilis were also compared in 2021. The fungicide residues of each treatment were detected.【Methods】The inhibitive effects of 13 different fungicides on the mycelia growth of C. shiraiana were determined. There were four replicates for each treatment, and the untreated PDA medium was served as the control. Those with better inhibitive effects were used in field trials. Four treatments were set up in Wuhan city, Hubei province in 2019. Carbendazim, prochloraz- manganese, pyraclostrobin · fluxapyroxad, and water as the control were used to evenly spray the whole mulberry tree canopy and surrounding ground for four times. The above treatments were randomly arranged with each treatment having 3 replicates. The corrected control efficiencies of different fungicides were investigated, and the fungicide residues were detected 20 days after the last spray. For calculation of the corrected control efficiency, nine branches of each mulberry tree were randomly selected, and the number of total and diseased fruits on each branch was recorded, sampling one meter in length. The effects of different fungicides, different control stages and biological control method were evaluated in Xiaogan city, Hubei province in 2021. Carbendazim, prochloraz-manganese, pyraclostrobin · fluxapyroxad, procymidone, and water as the control were used for the assessment of different fungicides efficiency. Prochloraz-manganese, the best efficiency and safe fungicide screened from the field experiment in 2019, was then used for the study on the effect at different control stages. The fungicide was sprayed at four different stages, February 23 (magpie mouth stage), March 3 (leaf opened stage), March 11 (flower spike formation stage) and March 22 (initial blooming stage), and the application was stopped on March 28 (full flowering stage). The corrected control efficiency of biological fungicides, T. harzianum and B. subtilis was compared. The treatments in 2021 were arranged randomly with 3 replicates for each treatment. The corrected control efficiencies of different fungicides were investigated, and the fungicide residues were detected 22 days after the last spray. For calculation of the corrected control efficiency, three branches from each mulberry tree were randomly selected, and the number of total and diseased fruits from each branch were recorded, sampling one meter in length.【Results】50% prochloraz-manganese and 42.4% pyraclostrobin·fluxapyroxad had the best inhibitory activity, with both showing EC50 of 0.01 µg ·mL^-1 , followed by 50% carbendazim, 50% iprodione, 30% pentazole · carbendazim and 50% procymidone, and 72% curzate had the lowest inhibitory activity, with EC50 of 15.10 µg·mL^-1 . In 2019, the corrected control efficiencies of 800 fold dilution of carbendazim, 1000 fold dilution of prochloraz-manganese and 2000 fold dilution of pyraclostrobin ·fluxapyroxad were 100%, 100% and 96.04%, respectively. The residues of carbendazim and prochloraz-manganese were 5.67 and 0.68 mg·kg^-1 , respectively. In 2021, the corrected control efficiencies of 800 fold dilution of carbendazim, 1000 fold dilution of prochloraz- manganese, 2000 fold dilution of pyraclostrobin · fluxapyroxad, and 1000 fold dilution of procymidone were 98.21%, 99.58%, 95.95% and 88.11%, respectively. The residues of carbendazim, prochloraz-manganese, and procymidone were 5.86, 0.68, and 2.94 mg·kg^-1 , respectively, and the residues of pyraclostrobin · fluxapyroxad was under detection. The corrected control efficiency of prochloraz-manganese sprayed at the magpie mouth stage, leaf opened stage, flower spike formation stage, and initial blooming stage was 96.98%, 97.65%, 96.39% and 91.40%, respectively. The corrected control efficiency at the initial blooming stage was significantly different from the above three stages. The fungicide residues at the four stages were 0.54, 0.49, 0.52 and 0.50 mg·kg^-1 , respectively. The corrected control efficiencies of 300 fold dilution of T. harzianum and 300 fold dilution of B. subtilis were 54.74% and 61.74% , respectively.【Conclusion】Carbendazim, prochloraz- manganese and pyraclostrobin · fluxapyroxad had the best corrected control efficiencies (above 95% ) in two years field trials. Procymidone had the lowest corrected control efficiency of 88.11%. The residues of carbendazim exceeded the standard, while prochloraz-manganese, pyraclostrobin ·fluxapyroxad and procymidone were found in the safe range. To prevent resistance of the pathogen to the fungicide, prochloraz-manganese and pyraclostrobin · fluxapyroxad can be sprayed alternately from the flower spike formation stage to 25-30 days before picking with an interval of 7 to 10 days. The method can safely and effectively control the disease, which can meet the food safety requirements. The efficiency of biological control is unsatisfactory and needs to be further explored and optimized.