What's eating my napa cabbage 'blues'?

Napa Cabbage 'Blues' is a club-root-resistant variety but has no resistance to its main insect pests. Diamondback moth, cabbage worms, aphids, and slugs are the primary threats. The same Bt-k and row cover program applies. Birds such as pigeons may also strip outer leaves in early spring.

Windowing on leaves from larvae feeding inside; progresses to full holes; particularly damaging in warm, dry seasons Bt-k or spinosad sprays every 7–10 days; pheromone traps to time spray applications accurately

Green caterpillars eat large irregular holes; frass inside wrapping leaves contaminates the head Bt-k spray applied thoroughly to both leaf surfaces; row cover; encourage parasitic wasps by planting umbellifers nearby

Dense grey-green colonies inside the developing head; sticky honeydew, sooty mold, and head quality loss Preventive row cover; insecticidal soap; remove heavily infested leaves promptly

Ragged tear-feeding on outer leaves down to midrib stubs; most damaging in late winter and early spring Bird-proof netting with mesh no larger than 25 mm; reflective tape or bird-scaring devices as deterrents