Composite Action Thresholds for the Control of Lepidopterous Pests on Fresh-market Cabbage in the Lower Rio Grande Valley of Texas

Various decision-making methods for controlling the complex of lepidopterous pests of cabbage, including Spodoptera exigua (Hübner), Trichoplusia ni (Hübner), and Plutella xylostella (L.), were evaluated in the lower Rio Grande Valley of Texas from October 1983 to March 1985. Large-scale tests in commercial cabbage fields demonstrated that an action threshold of 0.3 larvae per plant maintained damage below 1% of total harvested cabbage, similar to damage seen in conventionally scouted fields. On the average, two fewer insecticide applications were required in cabbage fields using the threshold of 0.3 larvae per plant compared with conventionally scouted fields. In small-plot tests, the action threshold of 0.3 larvae per plant and weekly pesticide applications resulted in equal yields. Both methods resulted in greater marketable yield than did either a damage-based threshold of one to three feeding sites per plant or no pesticide applications.