Screening Of Pesticide Formulations And Formulation Development For Effective Prevention And Control Of Rice And Wheat Sheath Blight

Rice sheath blight and wheat sharp eyespot,caused by Rhizoctonia,are the important diseases in rice and wheat.With the promotion of high-yield close planting techniques and the increase of nitrogen fertilizer application,these diseases are becoming more and more serious.At present,the controlling of such diseases relies mainly on the chemical agents,such as Azoxystrobin?Thifluzamide and Azole fungicide.However,long-term,massive and single use of the chelical agents make the pathogens have strong resistance to some of them,and the risk of the pathogens resistant to those disease are also increasing.In order to reduce the risk and improve the control effect of the fungicides on sheath blight and sharp eyespot,the agent,prothioconazole,developed by Bayer Ltd.was used to compound with the fungicides,commonly used in field,and a new mixture,24%prothioconazole tebuconazole SC,was developed.Results were as follows:1?The co-toxicities of prothioconazole mixed with different fungicides to Rhizoctonia were determined by mycelial growth rate method in vivo.When the mixtures composed with prothioconazole and tebuconazole with the mixing ratio of 2:1 or 3:1,the synergistic ratio(SR)values of the virulence to R.solani were 1.94 and 1.73,respectively,showing a significant synergistic effect.To Rhizoctonia cerealis,the synergistic effect was better when the two fungicides were mixed as 3:1 and 2:1,and the SR values were 1.88 and 1.92,respectively.The co-toxicities of the?ixture of prothioconazole and epoxiconazole to Rhizoctonia solani was strong as the ratio of 3:1,while the mixtures with the mixing ratios of 2:1,1:1.1:2 and 1:3 all had synergistic effect on R.cerealis,and the SR value was as high as 6.69 when the mixing ratio was 2:1.The SR value could reach 1.87 when the mixture composed with the mixing ratio of 1:3.When prothioconazole and thifluzamide were mixed with a mixing ratio of 1:2,the mixture had higher toxicity to R.cerealis.However,all the mixutres with different mixing ratios of prothioconazole and thifluzamide had no synergistic effect on R.solani.The mixtures of prothioconazole and pyraclostrobin had synergistic effect on R.solani and R.cerealis with the mixing ratio of 3:1 and 1:1,and the SR values were 1.92 and 3.73,respectively,while all the mixtures of prothioconazole and fludioxon had no synergistic effect on R.solani2>After screening of the wetting and dispersing agents,antifreeze,thickener,defoainer and other additives,we determined the best formulations of 24%prothioconazole.tebuconazole SC as below:24%raw pesticide(16%prothioconazole,8%tebuconazole),4%wetting-dispersant Featdis SCP,3%EFW,0.2%viscosity regulator Xanthan gum,1%magnesium aluminium silicate,4%ethylene glycol,0.1%defoamer,and then added water up to 100%.Quality control specification has been established according to formulation performance test.After been stored at 54±2? for 14 days,the characteristics of the suspension agent were listed as follwos:the suspension rate 95.2%.pH 6.9,average particle size 0.712?m,water splitting rate 2.3%and long-lasting foaming less than 25 mL.After been stored 0±2? for 7 days,the characteristics of the suspension agent were listed as follwos:the suspension rate 94.8%,pH 7.1,average particle size 0.871?m,lasting foaming less than 25 mL and viscosity be between 200 mPa·S to 600 mPa·S.3?Results of the field trial of fungicides showed that 450,600 and 750 g/ha of 24%prothioconazole tebuconazole SC had good control efficiency on rice sheath blight.Fifteen days after treatment,the control efficiency of these treatments can reach 68.66%,69.78%,and 79.10%,respectively.When the active ingredient content was 375,500 and 625 g/ha,fourteen days after treatment,the control efficiency was 64.76%,79.70%,90.22%and 74.17%?78.39%,86.27%on wheat sheath blight,respectively.The control efficiency of all the the mixture treaments was better than that of the single agent of prothioconazole and tebuconazole.All above results indicated that prothioconazole could be mixed with some fungicides commonly used in the field to enhance its toxicity against Rhizoctonia.24%prothioconazole tebuconazole SC developed in this study had excellent performance indexes and the potential for further industrial production and extensive application in the field.