Screen And Application Of Fungicide Mixtures Controlling Rice Blast(Magnaporyhe Grisea)

Rice blast disease caused by Magnaporthe grisea (Hebert) Barr. is the most economically important crop disease in China. Tebuconazole, kitazine, hinosan and iprobenfos were used to control rice blast in past decade years. However, there were some researchers reported that Magnaporthe grisea had developed resistance to kitazine, hinosan and iprobenfos gradually. Meanwhile, for the tricyclazole without therapeutic effect, it also often lost its efficacy controlling blast in some places in the case of the blasticide usage missed to prevent infection or the rainstorm caused wound. So it is very important to screen the better effective new fungicides or mixtures to control rice blast disease and study their use techniques.Tebuconazole, propiconazole and difenoconazole belong to the EBIs, ovraclostrobin, kresoxim-methyl and azoxystrobin belong to the Qols, tricyclazole and fenoxanil belong to the MBIs. We screened nine fungcides and tested their activites against Magnaporthe grisea in vitro and in vivo. The results showed that tebuconazole, propiconazole and difenoconazole strongly inhibited mycelia growth of M. grisea with EC50values from0.2186to0.8634μg/ml, while shenqinmycin, a antibiotic with new mode of action, could not inhibit mycelia growth significantly with EC50of6.9823μg/ml. Tricyclazole and fenoxanil had no direct inhibitory effects on mycelia growth, EC50values were more than50μg/ml, however, they effectively inhibited rice blast in vivo with EC50values of0.4465μg/ml and1.5795μg/ml. Ovraclostrobin, kresoxim-methyl and azoxystrobin effectively inhibited spore germination of M. grisea with EC50values from0.0367to0.935ug/ml.Then, some of them belong to EBIs, Qols and MBIs were selected to study their synergestic interaction for controlling Magnaporthe grisea. The activity of different rates of tricyclazole and tebuconazole mixed propiconazole inhibiting M. grisea was tested in vivo. The results showed that the rates of tricyclazole and tebuconazole mixed propiconazole from E to M displayed evident synergism, SR values were more than1.5. The other rates (A-D, N and O) of tricyclazole and tebuconazole mixed propiconazole showed additive effect. Different rates of tricyclazole and tebuconazole mixed with propiconazole (G, E, N and L) were formulated to44%,40%,10%and5%WP and WG, in the field trial test, they showed more than70%controlling effect against rice blast and exhibited certain yield-increasing effect. Meanwhile they can control rice sheath blight, rice false smut and rice leaf smut.Tebuconazole and difenoconazole both belong to the broad-spectrum, high activities, good systemic activity triazole fungicides, tricyclazole is the primary fungicide in controlling rice blast at present. Through fungicides mixtures screened in vivo, the mixture of tebuconazole and difenoconazole mixed tricyclazole(L) was found play evident synergism. The value of SR was1.673. The mixture inhibited mycelial growth and sporangia production, with average values of2.30and3.27μg/ml, respectively. Both protective and curative effects of the mixture to M. grisea were fine, with inhibition of disease spread value81.26%and40.96%separately at10jig/ml treatment. The mixture had a long persistence effect on M. grisea on rice and could last at least11days. After repetitious treatments, the control effect of mixture could last as long as15days. The mixture also has control effect on the wounded leaves and the mixture possessed a good residual performance.