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 complet e development on the plant in this greenhouse study. All plants expose d to larvae in the vegetative growth stage produced marketable heads a t harvest. A significant linear relationship was calculated for regres sion of beet armyworm density on cabbage head weight. A 95% confidence interval calculated on the mean response indicated that 15 beet armyw orms per plant significantly lowered head weight compared with no larv ae per plant. Plants infested in the cupping stage produced 47% market able heads at three larvae per plant and 27% marketable heads at 10 an d 17 larvae per plant. No significant relationship was found between l arval density and cabbage head weight for this growth stage. Plants in fested 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 highe r percentage of older leaves than younger leaves on cabbage plants in the vegetative and cupping growth stages.