Abstract: A composite and dynamic economic threshold (ET) model was established to manage the lepidopterous pest complex (Pieris rapae, Plutella xylostella, Spodoptera exigua, and Prodenia litura) of cabbage in Shanghai suburb. It included: (1)regressional equations of leaf fresh weight on cumulative degree-days, consideringcabbage variety and cabbage leaf type; (2) cabbageworm equivalency (ICE) of lepidopterous larvae, considering cabbage leaf types and larval age; (3) yield-loss sub-models, considering cabbage variety, cabbage developing stage, and cabbage leaf type. The economic yield loss levels are determined and applied as decision criteria in the determination of economic threshold in order to incorporate the effect of larval intraplant distribution. This ET model was evaluated in the field and allowed a 45% reduction in control cost with no yield difference.

Key words: Cabbage, lepidopterous pest complex, economic threshold