Agriculture: Cilantro and Parsley Pest Management Guidelines

Beet Armyworm

  • Spodoptera exigua
  • Description of the Pest

    Beet armyworm adults are 1/2 to 3/4 inch, nondescript brown moths. Adult moths lay 20 to 400 eggs in mass that they cover with their own light-colored scales, giving the masses a distinctive cottony appearance. When eggs first hatch, the pale green 1/16 inch (1.5 mm) long larvae feed for first few days in groups near the egg mass, skeletonizing or completely consuming leaves.

    As the larvae age, they disperse and move toward the center of the plant and feed singly. Older larvae vary in color but are usually a shade of olive green to black with many fine, wavy, light-colored broad stripes down the back on each side and may be up to 1.5 inches long. Often there is a dark spot on the side of the body just above the second true leg. The body surface is smooth and almost hairless.

    The larval stages last from 2.5 to 3 weeks at 70° to 80°F. Large larvae generally shelter in the center of the plant or underground during daylight hours. After five to six instars, the larvae burrow into the soil to pupate. The pupal stage persists 7 to 10 days but may be much longer when temperatures are cooler. Although newly emerged adults can be found throughout the year in central and southern California, major emergences and migration flights are usually observed in the spring through late summer. Beet armyworms numbers grow as weather warms and are most common on late summer and fall crops.

    Damage

    Beet armyworms can destroy seedlings, consume large portions of leaves, and stunt growth by feeding on developing buds. Young worms feed on leaves but rarely cause substantial damage. However, larger larvae feed on petioles and can cause significant crop loss. Large larvae are quite mobile and have been observed to travel over 10 feet per night, feeding on several plants. Beet armyworms also cause damage by contaminating cilantro or parsley with their bodies and frass, reducing crop marketability. In the San Joaquin Valley, fall populations are more damaging than spring populations.

    Management

    Cultural and biological controls help suppress armyworm numbers.

    Cultural Control

    Disc fields immediately following harvest to remove the food source for any remaining larvae. Some larvae and pupae will be directly killed by discing as well. Destroy weeds along field borders as armyworms often migrate from these areas into newly planted fields.

    Biological Control

    Naturally present predators and parasitoids can maintain armyworm numbers at low levels. Among the most common parasites are the wasps Hyposoter exiguae and Chelonus insularis, and the tachinid fly Lespesia archippivora. Armyworms can easily be checked for the presence of Hyposoter exiguae by pulling the larva apart and looking for the parasite larvae of light, translucent green color. Naturally occurring viral diseases can also play an important role. Diseased caterpillars first appear yellowish and limp. After death they hang from plants as shapeless, dark tubes oozing the disintegrated body contents.

    Organically Acceptable Methods

    Biological control and applications of Bacillus thuringiensis and the Entrust formulation of spinosad are organically acceptable management tools. Bacillus thuringiensis is most effective when applied on first and second instar larvae. Spinosad can be detrimental to natural enemies like syrphid flies, which are predators of aphids and other soft-bodied insects.

    Monitoring and Treatment Decisions

    Seedlings are susceptible to armyworm damage. Monitor fields frequently for beet armyworm from planting until harvest. Beet armyworm eggs and larvae are often easier to find on weeds in and near the field than in cilantro or parsley. Weeds can be pulled and readily examined whereas cilantro and parsley are often brittle and easily damaged during the early morning and late evening hours when larvae are active. Chenopodium species (e.g., lambsquarters, goosefoot) are particularly attractive to beet armyworm larvae.

    Begin monitoring for beet armyworm twice per week even before seedlings emerge.

    1. Check at least 25 plants in each quadrant of a 40- to 80-acre field. Fields smaller than 40 acres may require fewer samples.
    2. Check for egg masses and young larvae on pigweeds, lambsquarters, nettleleaf goosefoot, and other nearby weeds. If numbers are high on weeds, watch carefully for infestations on crop seedlings.
    3. Consider placing out pheromone traps (delta, wing, or bucket type) along field edges to monitor adult flights and predict egg laying.
    4. Once seedlings emerge or right after transplanting, check plants at least twice per week for armyworm egg masses and young larvae. Sample for armyworms along with cabbage loopers and include them in the total caterpillar count on your monitoring record.

    Most insecticides are more effective against young larvae than against eggs, so wait until the majority of eggs have hatched before treating. Treat plants when numbers of small larvae are large enough to impact plant growth. Beet armyworms are more difficult to control with insecticides than loopers. Make treatments when larvae are small; large larvae are more difficult to kill with compounds such as Bacillus thuringiensis. The best time for an insecticide treatment is in the evening hours because larvae become active at dusk, and sunlight degrades many pesticides.

    Broad-spectrum insecticides (e.g., methomyl) adversely affect natural enemies in most cases.

    Watch out for reports of insecticide resistance to certain pesticides (e.g. spinosad, methoxyfenozide, and others) in your area. To manage insecticide resistance in beet armyworm, limit the total number of sprays of each insecticide. The best way to do this is to practice the basic principles of IPM:

    • Monitor pests and maximize the use of biological and cultural controls.
    • Spray only when pest numbers warrant an application.
    • Use the most selective insecticides first to conserve natural enemy populations so they help with the control of pests.
    • Do not use insecticides with the same mode-of-action group number on successive beet armyworm generations.
    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. CHLORANTRANILIPROLE
      (Coragen) 3.5–5 fl oz 4 1
      MODE-OF-ACTION GROUP NUMBER1: 28
      COMMENTS: Foliar application; use with an effective adjuvant for best performance.
     
    B. SPINETORAM
      (Radiant SC) 5–8 fl oz 4 1
      MODE-OF-ACTION GROUP NUMBER1: 5
      COMMENTS: Toxic against some natural enemies (predatory thrips, syrphid fly larva, beetles) when sprayed and 5 to 7 days after. Control improved with addition of an adjuvant. Do not make more than two consecutive applications of Group 5 insecticides (spinetoram and spinosad).
     
    C. METHOXYFENOZIDE
      (Intrepid 2F) 4–10 fl oz 4 1
      MODE-OF-ACTION GROUP NUMBER1: 18A
      COMMENTS: An insect growth regulator. Do not apply more than 16 fl oz/acre per application or more than 64 oz/acre per season. See label for rotational crop restrictions.
     
    D. BACILLUS THURINGIENSIS ssp. AIZAWAI#
      (Xentari) 0.5–2 lb 4 0
      MODE-OF-ACTION GROUP NUMBER1: 11A
      COMMENTS: Registered on parsley, not on cilantro. Most effective against newly hatched larvae so proper treatment timing is essential.
     
    E. SPINOSAD
      (Entrust)# 1.25–2 oz 4 1
      (Success) 4–6 oz 4 1
      MODE-OF-ACTION GROUP NUMBER1: 5
      COMMENTS: Do not apply when aphids are present because it can harm their natural enemies, especially syrphid fly larvae. Do not make more than 3 or 5 applications per crop. See label.
     
    F. INDOXACARB
      (Avaunt) 3.5–6 oz 12 3
      MODE-OF-ACTION GROUP NUMBER1: 22
      COMMENTS: Registered on parsley, not on cilantro. Use to control low numbers.
     
    G. EMAMECTIN BENZOATE*
      (Proclaim) 2.4–4.8 oz 12 7
      MODE-OF-ACTION GROUP NUMBER1: 6
      COMMENTS: Registered on parsley, not on cilantro.
     
    H. METHOMYL*
      (Lannate SP) 0.5–1 lb 48 10
      (Lannate LV) 1.5–3 pt 48 10
      MODE-OF-ACTION GROUP NUMBER1: 1A
      COMMENTS: Registered on parsley, not on cilantro. Will also control loopers.
     
    I. PERMETHRIN*
      (Pounce 25WP) 6.4–12.8 oz 12 1
      MODE-OF-ACTION GROUP NUMBER1: 3A
      COMMENTS: Registered on parsley, not on cilantro. Apply a minimum of 5 gal of finished spray/acre by aircraft, 15 gal/acre with ground equipment.
      . . . or . . .
      (Ambush 25WP) 6.4–12.8 oz 12 1
      MODE-OF-ACTION GROUP NUMBER1: 3A
      COMMENTS: Registered on parsley, not on cilantro. Do not apply more than 2 lb a.i./acre per season. Do not graze treated areas or feed crop residues to livestock.
     
    J. ZETA-CYPERMETHRIN*
      (Mustang) 3.4–4.3 fl oz 12 1
      MODE-OF-ACTION GROUP NUMBER1: 3A
      COMMENTS: Not for use on cilantro grown for seed. Do not exceed 0.3 lb a.i./acre per season.
    ** See label for dilution rates.
    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 two intervals is the minimum time that must elapse before harvest.
    # Acceptable for organically grown produce.
    1 Rotate chemicals 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; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
    * Permit required from county agricultural commissioner for purchase or use.
    Text Updated: 12/15
    Treatment Table Updated: 01/19