This is the first report on the suppression of PWD by OA. The result strongly indicates that PWD could be controlled by antibacterial antibiotic alone and a combination of antibacterial and nematicidal agents.

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Plant extracts from 50 plant species were tested for their nematicidal activities against Bursaphelenchus xylophilus, the causative agent of pine wilt disease. Out of 50 extracts, the methanol extract of Myristica malabarica fruit rinds showed the most potent nematicidal activity with mortality of 100% at a concentration of 1000 μg ml −1 against B. xylophilus. Three nematicidal substances were isolated by bioassay-guided fractionation and then identified as malabaricones A, B and C by mass and NMR spectral data. Both malabaricones B and C showed higher activity than malabaricone A. There was a significant synergistic interaction between the three compounds on the pine wood nematode. When the combination of three compounds at a ratio of 1 : 1 : 1 was applied, its EC 50 value was 11.8 μg ml −1 . These results indicate that the extract of M. malabarica containing the three resorcinols could be useful as a natural nematicide for the control of pine wilt disease.