Research On Chemical Control Technology Of Mulberry Sclerotini

Mulberry fruit sclerotiniosis is the main disease affecting mulberry yields,and occurs in planting bases all over the country with an incidence of 90% or more,which has caused devastating damage to the fruit mulberry industry and restricted the development of the mulberry industry.At present,the production mainly relies on Carbendazim or Thiophanate-Methyl and other fungicides for chemical control,which plays an important role in the production.In recent years,it was been found that the control effect decreased year by year with the increase of the use years of Carbendazim or Thiophanate-Methyl in fields control of mulberry fruit sclerotiniosis,and the pathogens developed resistance to Carbendazim and Thiophanate-Methyl during the indoor pesticides screening.Therefore,in this study,we isolated and identified the pathogens of mulberry fruit sclerotiniosis in the main mulberry yields in Wanzhou district,Chongqing.Risk assessment tests were conducted for pathogens resistance to Carbendazim and Thiophanate-Methyl.20 commercially available fungicides were selected to control mulberry fruit sclerotiniosis by indoor and fields.Fungicide residues trials were detected for mulberries in treated areas,and safety evaluation experiments of silkworms were carried out.In this paper,the chemical control techniques for mulberry fruit sclerotiniosis were summarized to provide scientific basis for prevention and control of mulberry fruit sclerotiniosis in production.The main research results obtained are as follows:(1)The pathogenic bacteria collected from mulberry yields in Ganning town(Ganning Base of Chongqing Three Gorges Agricultural Science Academy and Guanfeng village),and Wuling town,and Fenshui town.were isolated and purified,pathogenicity determined,morphology and molecular biology identified.It was determined that Sclerotinia Sclerotiorum was the main pathogenic bacteria in Wanzhou district.(2)The differentiated dose method was used to determine the resistance of strains of Sclerotinia Sclerotiorum.The results showed that 29 strains of sclerotinia sclerotiorum had high resistance to Thiophanate-Methyl and Carbendazim,and the average frequency of resistance to Thiophanate-Methyl and Carbendazim was 93.1 % and 100 %,respectively.(3)The indoor virulence of 20 fungicides against Sclerotinia Sclerotiorum was determined by mycelium growth rate method.The results showed that all fungicides had different degrees of inhibition on the mycelia of Sclerotinia Sclerotiorum.Among them,2% Kasugamycin AS 、 80% Mancozeb WP,33.5% Oxine Copier SC,0.4 g/ml Pyrimethanil 和 3% Zhongshengmycin WP had poor bacteriostasis effect on mycelial inhibition.The other 15 fungicides had better bacteriostatic effect on mycelial inhibition,so they can be applied to field trials.(4)The field efficacy and safety evaluation experiments of 15 fungicides screened indoors against mulberry fruit sclerotiniosis were carried out.The results showed that 13 fungicides had good control effect on mulberry fruit sclerotiniosis,and control effects were more than 90%.Among them,0.25 g/ml Prochloraz EC 1500 times liquid,0.43g/ml Tebuconazole SC 2000 times liquid,40% Myclobutanil WP 1500 times liquid cause phytotoxicity on mulberries.The residual amount of fungicides in these treated areas which included 40% Myclobutanil WP 1500 times liquid,50% Boscalid WG 1000 times liquid,etc 10 kinds of fungicides were lower than the limit of quantification,or were detected no fungicide.30% Pyraclostrobine SC 1500 times liquid,22.5% Picoxystrobin SC 1500 times liquid had strong acute toxicity to silkworms.In conclusion,50%Boscalid WG 1000 times liquid and 40% Myclobutanil WP 1500 times liquid should be preferred using in the chemical control of mulberry fruit sclerotiniosis.10%Difenoconazole WG 1500 times liquid,30% Pyraclostrobine SC 1500 times liquid,22.5% Picoxystrobin SC 1500 times liquid,0.25 g/ml Azoxystronbin SC 1000 times liquid,20% Penthiopyrad SC 1500 times liquid and 24% Fenbuconazole SC 1000 times liquid should be alternated using,among them,Do not use 30% Pyraclostrobine SC 1500 times liquid and 22.5% Picoxystrobin SC 1500 times liquid in both fruit and leaf mulberry yields.