Horseradish-Imported cabbageworm

Pieris rapae

Pest description, crop damage and life history


Pest monitoring The following information is from California but is generally applicable in the Pacific Northwest: Cabbageworms can be monitored at the same time as cabbage loopers. Sample 25 plants selected randomly throughout the field. Although treatment levels combine the two species, cabbageworms may be harder to find because of their smaller size and their inconspicuous coloring. Look for small larvae and eggs on the undersides of leaves. Larger worms feed toward the center of the plant, often near the midribs of leaves. Good clues to cabbageworm presence include their greenish brown fecal pellets or many white cabbage butterflies fluttering around the field (check for eggs in a few days).

Base treatment on numbers of healthy larvae present. Treat seedlings or small plants if populations of medium-size to large caterpillars are high enough to stunt growth.

Management-biological control

Natural enemies can assist significantly in the control of imported cabbageworm. Important parasites include the pupal, larval, and egg parasites in the Trichogramma genus, as well as tachinid flies. Timely mass releases of commercially available trichogramma during peak flight can be an effective control agent. Viruses and bacterial diseases are also sometimes important control factors in the field. If possible, use Bacillus thuringiensis to avoid adverse impact on natural enemies. Bt is very effective against imported cabbageworm, especially when applied to young (early-instar) caterpillars.

Management-cultural control

Make new plantings as far as possible from those of the previous year. At the end of the year, harvest crops without delay. Plowing under or destroying plant residues at this time eliminates an important food source for the overwintering generation of cabbageworms.

Management-chemical control: HOME USE

  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • bifenthrin
  • carbaryl
  • cyfluthrin
  • kaolin-Applied as a spray to foliage and stems, it acts as a repellent to some insect pests. Some formulations are OMRI-listed for organic use.
  • permethrin
  • pyrethrins-Some formulations are OMRI-listed for organic use.
  • spinosad-Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin

Management-chemical control: COMMERCIAL USE

  • alpha-cypermethrin (Fastac EC) at 0.02 to 0.025 lb ai/A. PHI 1 day. REI 12 hr. Retreatment interval 4 days. Do not exceed 0.075 lb ai/A per season.
  • Bacillus thuringiensis (Javelin) at 0.12 to 1.5 lb/A. PHI 0 days. REI 4 hr. Acts slowly; may need multiple applications. Add an appropriate spreader-sticker to enhance control. Most effective on small larvae. Some formulations are OMRI-listed for organic use.
  • bifenthrin (Brigade 2EC) at 0.08 to 0.1 lb ai/A. PHI 21 days. REI 12 hr. Retreatment interval 7 days. Do not exceed 0.5 lb ai/A per season.
  • GS-omega/kappa-Hxtx-Hv1a (Spear Lep) at 0.8 lb ai/A. PHI 0 days. REI 4 hr. Do not exceed 2 lb ai/A per year.
  • zeta-cypermethrin (Mustang) at 0.04 to 0.05 lb ai/A. PHI 1 day. REI 12 hr. Do not exceed 0.3 lb ai/A per year.