BEET ARMYWORM (LEPIDOPTERA, NOCTUIDAE) FEEDING IMPACT ON CABBAGE DEVELOPMENT AND MARKETABILITY

Cabbage plants in three growth stages were infested with third-instar beet armyworms, Spodoptera exigua (Hubner), at four densities ranging from 0 to 17 larvae per plant. Larvae were allowed to feed and complete development on the plant in this greenhouse study. All plants exposed to larvae in the vegetative growth stage produced marketable heads at harvest. A significant linear relationship was calculated for regression of beet armyworm density on cabbage head weight. A 95% confidence interval calculated on the mean response indicated that 15 beet armyworms per plant significantly lowered head weight compared with no larvae per plant. Plants infested in the cupping stage produced 47% marketable heads at three larvae per plant and 27% marketable heads at 10 and 17 larvae per plant. No significant relationship was found between larval density and cabbage head weight for this growth stage. Plants infested in the heading stage produced fewer marketable heads as larval densities increased, ranging from 74 to 14% marketable heads at three and 17 larvae per plant, respectively. Beet armyworms consumed a higher percentage of older leaves than younger leaves on cabbage plants in the vegetative and cupping growth stages.