Abstract: A growth promoter according to the present invention that can be applied to a plant other than solanaceous plants is a plant growth promoter utilizing potato cyst nematodes and contains a fatty acid dialkanolamide represented by the following general formula (1) as a substance that acts on the potato cyst nematodes: R—CO—N(—R?—OH)(—R?—OH)??(1) (in the general formula (1), R represents an alkyl group that has 1 to 20 carbon atoms and may be substituted, and R? and R? may be the same or different from each other and each represent an alkylene group that has 1 to 10 carbon atoms and may be substituted). When the plant growth promoter of the present invention is sprayed on the soil where the eggs of potato cyst nematodes are present, potato cyst nematodes hatched by the effect of the above-described fatty acid dialkanolamide contained in the plant growth promoter promote the growth of a non-host plant.