Agriculture: Asparagus Pest Management Guidelines

Armyworms

  • Beet armyworm: Spodoptera exigua
  • Western yellowstriped armyworm: Spodoptera praefica
  • Description of the Pest

    Beet armyworms may be abundant on asparagus ferns in low desert valleys of Imperial and Riverside counties any time from May to October. In other locations they are relatively minor pests. The adult is a small, mottled gray or dusky-winged moth. Females deposit pale greenish or pinkish, striated eggs on the asparagus ferns in small or large masses covered with white cottony material. The eggs hatch in a few days, and the tiny caterpillars begin feeding on the cladophylls (branchlets) in the plant canopy. Larger larvae feed on the epidermis of the branches of the ferns. The caterpillars become full grown in about 2 to 3 weeks and are about 1.25 inches long. They may be olive green to almost black in color with a yellow stripe on each side of the body. Beet armyworms may become abundant and cause severe injury to asparagus ferns in summer and fall.

    Western yellowstriped armyworm may be abundant on asparagus ferns in low desert valleys of Imperial and Riverside counties anytime from June through October but in other areas is a relatively minor pest. The adult is a small, mottled gray or dusky-winged moth. Females deposit eggs, laid in clusters and covered with a gray, cottony material, on the asparagus. The eggs hatch in a few days, and the tiny caterpillars begin feeding on the cladophylls (branchlets) in the plant canopy. Larger larvae feed on the epidermis of the fern's branches. The caterpillar is usually black with two prominent stripes and many narrow bright ones on each side. At maturity it is about 1.5 to 2 inches long.

    Damage

    Larvae feed mostly at night on the epidermis of asparagus fern branches, often girdling the branch and causing the ferns to die.

    Management

    Good weed management can help prevent the buildup of armyworms. Treatments may be necessary when armyworms are in the field and damage is occurring.

    Organically Acceptable Methods

    Sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for use on an organically certified crop.

    Monitoring and Treatment Decisions

    Armyworm eggs and larvae are easier to find on weeds near asparagus fields than in the fields when the ferns are large. Chenopodium spp. (e.g., lambsquarters, goosefoot) are particularly attractive to beet armyworm during fern stage. Monitor fields twice weekly because populations can build quickly. Adult beet armyworm activity can be monitored by using pheromone traps placed along the edges of fields. This technique is good for detecting populations of migrating moths.

    Treat when larvae are visibly present in the ferns. Treatments are most effective when larvae are small; large larvae are more difficult to kill, especially with Bacillus thuringiensis products. Treat at dusk or at night; larvae are more active at dusk until twilight, and insecticides such as Bacillus thuringiensis products are susceptible to photodegradation.

    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: Do not apply more than 15.4 fl oz Coragen or 0.2 lbs a.i. of products containing chlorantraniliprole/acre/crop.
     
    B. BACILLUS THURINGIENSIS ssp. AIZAWAI#
    (various products) Label rates 4 0
    MODE-OF-ACTION GROUP NUMBER1: 11A
    COMMENTS: Apply when armyworms are small. Not harmful to natural enemies.
     
    C. METHOMYL*
    (Lannate LV) 1.5–3 pt 48 1
    (Lannate SP) 0.5–1 lb 48 1
    MODE-OF-ACTION GROUP NUMBER1: 1A
    COMMENTS: Apply at 5–7 day intervals as needed. Do not apply more than 4.5 lb a.i./acre/crop.
     
    D. SPINOSAD
    (Entrust)# 1.25–2 oz 4 See comments
    (Success) 4–6 fl oz 4 See comments
    MODE-OF-ACTION GROUP NUMBER1: 5
    COMMENTS: Make applications only to asparagus ferns; do not apply within 60 days of spear harvest. Do not apply more than 0.28 lb a.i./acre/crop. Check with organic certifier to determine which products are organically acceptable.
     
    E. CARBARYL
    (Sevin Bait 5%) Spears: 20 lb
    Ferns: 40 lb
    12 1
    MODE-OF-ACTION GROUP NUMBER1: 1A
    COMMENTS: Use in fields where armyworms are migrating into the asparagus field from another crop. Repeat 7–14 days later if necessary. Ground application.
     
    F. PERMETHRIN
    (Ambush, Pounce) 3.2–6.4 oz 12 1
    MODE-OF-ACTION GROUP NUMBER1: 3
    COMMENTS: Apply by ground equipment only. Do not apply more than 0.4 lb a.i./acre/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.
    * Permit required from county agricultural commissioner for purchase or use.
    # Acceptable for use on organically grown produce.
    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).
    Text Updated: 06/09
    Treatment Table Updated: 08/19