Screening On Twenty-six Single Fungicides And Mixed Fungicides Against Rubber Powdery Mildew

Rubber powdery mildew, one of the most commercially important diseases of rubber trees in our country, is caused by Oidium heveae, an obligate parasite which can be determined only in vivo.Inoculation method for fungicidal bioassay of Oidium heveae was for the first time studied. A comparison between spraying, shaking off and brushing spores was drawn, variation of disease index and control effect of 10mg/L triadimefon on Oidium heveae with different inoculation concentrations was detected. Combination with the both tests led to a conclusion that inoculation method of spraying spores at concentration of 5×104-10×104spores/mL brought the most stable and repeatable result.Determination on toxicity of twenty-six fungicides to Oidium heveae was carried out in 2008-2009. Results showed that pyraclostrobin, SYP-4155, SYP-3759, kresoxim-methyl, SYP-1620, SYP-3343, triflumizole, azoxystr-obin, epoxiconazole, tetraconazole, flusilazole and ethirimol inhibited spore germination more strongly than triadimefon. Given the ability to suppress hyphal growth, triflumizole, SYP-3343 and SYP-3759 were better than triadimefon, and epoxiconazole, SYP-4155, flusilazole and pyraclostrobin were similar to triadimefon, while tetraconazole was slightly worse than triadimefon. The results led to a conclusion that triflumizole, SYP-3343, SYP-3759, epoxiconazole, SYP-4155, flusilazole, pyraclostrobin and tetraconazole are hopeful candidate fungicides for controlling rubber powdery mildew. The results also indicated that the category of funcides screened by means of spore germination inhibition test, which refelected fungicidal activity to a certain extent, included more than that by determination in vivo.Sun Yunpei's method was employed to test synergistic ratio of mixture fungicides qualitatively analyzed by way of Horsfall's, results of the two kinds of methods mostly overlapped. Proved synergistic ratio of mixture fungicides were as follows:ratio of epoxiconazole and pyraclostrobin 6:4,8:2, ratio of tetraconazole and SYP-3759 1:9-4:6, ratio of triadimefon and SYP-3759 9:1, ratio of triflumizole and SYP-3759 8:2, ratio of flusilazole and SYP-3343 7:3-9:1, ratio of tetraconazole and SYP-3343 6:4, ratio of triadimefon and SYP-3343 5:5,8:2, ratio of triflumizole and SYP-3343 7:3-8:2, ratio of tetraconazole and SYP-4155 9:1, ratio of triflumizole and SYP-4155 8:2-9:1.