[Aim]  To determine the best month to deploy hanging yellow sticky-board traps for capturing tea green leafhoppers (Empoasca onukii), while minimising capture of mymarid wasps, which are a natural enemy of this pest. [Methods]  Hanging sticky-board traps were deployed in three different months in spring and autumn and the number of tea green leafhoppers and mymarids captured was recorded and compared. The number of nymphs under leaf buds was investigated in the field. [Results]  When traps were deployed in the middle of spring (mid to late March), by the end of March the benefit-to-harm ratio (mymarids to tea green leafhoppers) was > 1. Deploying traps in early April resulted in the greatest number of tea green leafhoppers being trapped in early June. Peak abundance of the tea green leafhopper occurred from early May to early June, during which period the number of the tea green leafhoppers captured was significantly lower than in the control (P < 0.01), which was 29.51% to 32.89%, and the ratio of benefit to harm was < 0.5. In early May, there was no significant difference between the number of insects caught relative to the control (P > 0.05), and the benefit to harm ratio gradually increased from 0.49 to 0.67. In late August, the number of trapped mymarids gradually increased, and the benefit to harm ratio was 0.47 in early September. Traps deployed from early September to late October captured significantly fewer tea green leafhoppers in October (35.10%-38.14%) than the control (P < 0.01). When traps were deployed from late September to early November there was no significant difference in the number of tea green leafhoppers captured relative to the control (P > 0.05). [Conclusion]  Yellow sticky-board traps should be hung in tea plantations when the tea green leafhopper begins to appear; in early April and early September. It is best to deploy these traps from early April to late May in spring, and from early September to late October in autumn.