Comparison of Action Thresholds for Lepidopterous Larvae on Fresh-Market Cabbage1

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Abstract
Five different action thresholds for control of lepidopterous larvae on fresh-market cabbage were compared in Wisconsin and New York, and in Ontario, Canada, in 1981. An average of the three locations revealed that a threshold of one or more new feeding sites per head (Florida threshold) required far less time to assess and received the fewest insecticide applications (1.3), but also allowed the most injury. All other thresholds received three to four applications and provided acceptable and similar levels of marketability. Thresholds based on (1) egg and larval counts of imported cabbage worm (ICW), Pieris rapae (L.), and cabbage looper (CL), Trichoplusia ni (Hubner), and (2) feeding injury by larvae of ICW, CL, and diamondback moth (DB), Plutella xylostella (L.), required nearly 2A-fold the evaluation time of the Florida threshold. A threshold based on 50% of sampled plants infested with any larvae of the three species required 1.6-fold the assessment time of the Florida threshold. A fortnightly insecticide application, without regard to insect pressure, provided results similar to all other thresholds, except that of Florida.