Resistance of melon powdery mildew isolates to kresoxim-methyl in Guangxi and determination of its sensitivity to three fungicides.

【Objective】The resistance level, distribution and development of melon powdery mildew isolates to kresoximmethyl in Guangxi were identified and effective alternative fungicides were screened to provide references for prevention and controlling of melon powdery mildew. 【Method】From 2007 to 2012, bitter gourd, wax gourd, muskmelon, cucumber and bottle gourd disease samples were collected from Nanning, Guiping, and Beihai, etc. Their isolates' resistance to kresoximmethyl were detected by leaf disk tests. Sensitivity of high-resistant isolates to carbendazim, trifloxystrobin and propineb were also analyzed. 【Result】The results showed that 83 melon powdery mildew population produced resistance to kresoximmethyl in varying degrees. Resistant isolates were mainly distributed in bitter gourd powdery mildew and their resistant frequency was the highest(63.89%), while bottle gourd isolates had the lowest resistant frequency(6.67%). The resistant level of bitter gourd powdery mildew against to kresoxim-methyl increased gradually from 2007 to 2012 in Nanning City, resulting in development of high-resistance population. Fungicide screening assay results indicated that powdery mildew isolates with highly resistant to kresoxim-methyl, were highly drug-fast to carbendazim and cross-resistant to trifloxystrobin, but was sensitive to propineb. 【Conclusion】In Guangxi, melon powdery mildew isolates were highly resistant to kresoxim-methyl and alternate use of propineb in the production process could be recommended.