Agriculture: Cole Crops Pest Management Guidelines

Imported Cabbageworm

  • Pieris rapae
  • Description of the Pest

    Larvae (caterpillars) are green with numerous fine hairs that give their skin a velvety appearance. Older larvae may be up to 1 inch long, and often have one faint yellow-orange stripe along their back and broken stripes along the sides. Compared to other caterpillars, cabbageworms move slowly and are sluggish. They feed voraciously on both the outer and inner leaves, often feeding along the midrib, at the base of the wrapper leaves, or boring into the heads of cabbage.

    After feeding for about 2 to 3 weeks, larvae pupate attached to their host by a few silk strands. Pupae are green with faint yellow, lengthwise lines; there is no dense silk covering or cocoon.

    The adult cabbage butterfly is white to pale yellowish with a wingspan of 1.5 inches and has one to four black spots on each forewing. Adults are often seen fluttering around fields and blossoming, low-growing plants. Adult females lay whitish, elongated eggs singly on the undersides of leaves. Eggs are pointed at the top and have pointed ridges down the sides.

    The cabbageworm has several generations per year. It can be active throughout the year where hosts are present.

    Damage

    Cabbageworm larvae chew seedlings and large, irregular holes in leaves, bore into heads, and may contaminate marketed produce with greenish-brown fecal pellets. Most economic damage is to the marketed plant parts.

    Management

    Closely watch seedlings, which quickly become damaged if the pest becomes abundant.

    Between thinning or transplanting and heading, cole crops tolerate considerable damage from caterpillars eating leaves. During this time, sample frequently enough to assess numbers accurately and avoid unnecessary insecticide application that can disrupt biological control.

    Once plants begin to head, even low numbers of imported cabbageworm can cause serious economic damage and may require insecticide application.

    Cultural Control

    To prevent imported cabbageworms from migrating into the crop, control cruciferous weeds (such as mustards) that can host them.

    Biological Control

    Important natural enemies include the pupal parasite Pteromalus puparum, the larval-parasitic wasps Apanteles glomeratus and Microplitis plutellae, several tachinid flies, and egg-parasitic Trichogramma species. Natural viral infections may also provide effective control.

    Consider installing insectary plants to attract natural enemies. Avoid the use of broad-spectrum insecticides that disrupt the biological control of imported cabbageworm by natural enemies.

    Organically Acceptable Methods

    Use biological control, cultural control, and sprays of Bacillus thuringiensis and the Entrust SC formulation of spinosad in an organically certified crop.

    Monitoring and Treatment Decisions

    Combine monitoring of imported cabbageworm with monitoring for cabbage looper. Compared with cabbage looper, imported cabbageworm may be harder to find because its maximum size is smaller than other caterpillars and its green color is inconspicuous on plants.

    In a weekly basis beginning at seedling emergence or right after transplanting, check 25 plants selected randomly throughout the field.

    • Note the time when many adults (butterflies) are fluttering around the field. A few days later, check plants for eggs and small larvae on the underside of leaves.
    • Look for larger caterpillars toward the center of the plant where they often feed near the midrib of leaves.
    • Look for greenish-brown fecal pellets.

    Base treatment on the combined number of healthy imported cabbageworm and cabbage looper larvae found.

    • In the early stages of crop development, apply an insecticide if medium-sized to large caterpillars are numerous enough to stunt growth (approximately 1 caterpillar for every 5 plants).
    • Prior to heading on well-established crops (except for Brussels sprouts), do not apply insecticide unless more than 9 caterpillars are found per plant.
      • For Brussels sprouts, apply insecticide just before heading or at Brussels sprouts formation if 1 or more caterpillars is found in 25 plants.
    • From heading to harvest, apply insecticide if more than 10% of the sampled plants (2–3 plants out of 25) are infested with at least 1 caterpillar.

    Where possible, use Bacillus thuringiensis to avoid harming natural enemies. Bacillus thuringiensis is very effective against imported cabbageworm and cabbage looper, especially when applied to early-instar (young) larvae. If significant numbers of beet armyworm, diamondback moth, or cutworms are also present, use a broad-spectrum insecticide recommended for these species to also control imported cabbageworm.

    Common name Amount per acre REI‡ PHI‡
    (Example trade name) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
     
    A. BACILLUS THURINGIENSIS ssp. KURSTAKI
      (Condor WP)# 0.5–2 lb 4 0
      MODE-OF-ACTION GROUP NUMBER1: 11A
      COMMENTS: Not registered for use on broccoflower (cavalo), mizuna, and mustard spinach. Check with organic certifier to determine which products are organically acceptable. Label strongly recommends an approved spreader-sticker for application in cole crops.
     
    B. CHLORANTRANILIPROLE
      (Coragen) 3.7–7.5 fl oz 4 3
      MODE-OF-ACTION GROUP NUMBER1: 28
      COMMENTS: Foliar application; use with an effective adjuvant for best performance. Use higher application rates within this range for heavier infestations, larger or denser crops, or extreme environmental conditions such as rainy weather or high temperatures.
     
    C. SPINETORAM
      (Radiant SC) 5–10 fl oz 4 1
      MODE-OF-ACTION GROUP NUMBER1: 5
      COMMENTS: Toxic against some natural enemies (predatory beetles, syrphid fly larvae, and predatory thrips) when sprayed and 5 to 7 days after. Control improved with addition of an adjuvant.
     
    D. SPINOSAD
      (Entrust SC)# 3–6 fl oz 4 1
      (Success) 3–6 fl oz 4 1
      MODE-OF-ACTION GROUP NUMBER1: 5
      COMMENTS: Toxic against some natural enemies (predatory beetles, syrphid fly larvae, and predatory thrips) when sprayed and 5 to 7 days after. Must be applied when eggs are present or larvae are small. For organic formulations, check with organic certifier to determine which products are organically acceptable.
     
    E. METHOXYFENOZIDE
      (Intrepid 2F) See comments 4 1
      MODE-OF-ACTION GROUP NUMBER1: 18
      COMMENTS: Use a rate of 4–8 fl oz per acre for early-season applications to young crops. Use a rate of 8–10 fl oz per acre for mid- to late-season infestations and heavier infestations.
     
    F. EMAMECTIN BENZOATE
      (Proclaim) 2.4–4.8 oz 12 See comments
      MODE-OF-ACTION GROUP NUMBER1: 6
      COMMENTS: PHI is 7 days for head and stem cole crops and 14 days for leafy cole crops.
     
    G. INDOXACARB
      (Avaunt) 2.5–3.5 oz 12 3
      MODE-OF-ACTION GROUP NUMBER1: 22
      COMMENTS: Add a wetting agent to improve coverage. Minimum interval between sprays is 3 days.
     
    H. CRYOLITE
      (Prokil Cryolite 96) 8–16 lb 12 See comments
      MODE-OF-ACTION GROUP NUMBER1: 8C
      COMMENTS: For use on broccoli, Brussels sprouts, cabbage, and cauliflower. Use on cabbage is allowed based on a supplemental label (EPA Reg. No. 10163-41). For broccoli, Brussels sprouts, and cauliflower, preharvest interval is 7 days. For cabbage, preharvest interval is 14 days. Must be ingested by the insect. Apply when early instars are present. Can be useful in an insecticide resistance-management program.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
    1 Rotate insecticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
    # Acceptable for use on organically grown produce.
    * Permit required from county agricultural commissioner for purchase or use.
    Text Updated: 12/20
    Treatment Table Updated: 12/20