| Rice sheath blight, rice blast and rice bacterial leaf blight are the three major diseases of rice, with Short-stalked variety are grown and cultivation levels increased in recently the occurrence of rice sheath blight has been increasing and already had become the first disease on rice. Rice sheath blight (Rhizoctonia solani) is a fungal disease which occurs mainly from rice tillering stage to mature stage. Rice sheath blight can infect rice leaf sheaths, bladesand ear of rice, decrease the yield and quality of rice. chemical control is an important means of controlling rice sheath blight with, but the main fungicide used to control rice sheath blight is valrdamycin and its mixture. The different mixtures of pesticides by re-sereening were not only control the occurrence of disease,but also can delay the bacteria resistance.Accordingly, six Single doses(validamycin, thifluzamide,hexaconazole, propiconazole, azoxystrobin, Bacillus subtilis B-916) and two mixtures(azoxystrobin and hexaconazole, validamycin and Bacillus subtilis) were tested by mycelial growth rate method, the Sclerotia germination experiment and the pot experiment to assess the toxicity and field efficacy. These experiments can provide a scientific basis to resistance management of rice sheath blight,the main research methods and results could be summarized as follows:Under laboratory conditions, toxicities of a validamycin, thifluzamide,hexaconazole, propiconazole, azoxystrobin, Bacillus subtilis B-916 to Rhizoctonia solania were tested using mycelial growth rate method,the Sclerotia germination experiment and the pot experiment. The results showed that among the six fungicides, thifluzamide showed the highest toxicity to R. solania with the median effective concentration (EC50) value of 3.0201?g/mL, inhibition rate is 86.13%,virulence regression equation is y=4.6369+0.7564x; azoxystrobin has the stronges inhibition rate on sclerotia germination was 33.67%;thifluzamide had greatest impact against Rhizoctonia virulence, the inhibition rate reached 81.1%.Using the method of SR values obtained the azoxystrobin and hexaconazole best mixture proportioning was 1:2, SR was 1.55, EC50 just 0.00719?g/mL; validamycin bacillus subtilis mixture ratio was 1:1,SR wasl.81, EC50 was 109.77?g/mL?The result showed that two kinds of mixtures against rice sheath blight mycelial growth inhibition rates were 92.12%and 90.87%, inhibition rates were21.33% and 26.33% on sclerotia germination, virulence inhibition rate against rice sheath blight reached 84.06% and 79.03%. It can be seen that the mixtures control effects are better than single- dose, so using mixtures control rice sheath blight has certain advantages than single- dose.According to the field trials guidelines, using six kinds of single-dose and two mixtures was sprayed twice to verify field efficacy. The results showed that the two kinds of mixtures had the best control effect especially is 24% azoxystrobin-hexaconazole suspension concentrate (72mL/hm2) have 85.29% control effect after the second sparying.25% azoxystrobin suspension concentrate(250ml/hm2) have best control effect in single-dose can reached 81.21% after the second sparying,20% validamycin soluble powder (150g/hm2) had the lowest control effect is only 56.10%. the other pesticide's efficiency was between 62.43%-78.44%, the secondary control efficiency were higher than the first control effect. Therefore we recommended to use 24% azoxystrobin-hexaconazole SC(72mL/hm2) or 25% azoxystrobin SC(250ml/hm2) according to the rules of second spraying after 7 days since the first spraying to achieve the best control effect. |
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