How to Manage Pests

UC Pest Management Guidelines

Asparagus

Armyworms

Scientific name:
Western yellowstriped armyworm: Spodoptera praefica
Beet armyworm: Spodoptera exigua

(Reviewed 6/09, updated 2/12)

In this Guideline:


DESCRIPTION OF THE PESTS

Beet armyworms may be abundant on asparagus ferns in low desert valleys of Imperial and Riverside counties anytime 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 build up 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 photo degradation.

Common name Amount per Acre** R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy, information related to natural enemies and honey bees and environmental impact. Not all registered pesticides are listed. Always read label of 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: 11.B1
  COMMENTS: Apply when armyworms are small. Not harmful to natural enemies.
 
C. CHLORPYRIFOS*
  (Lorsban Advanced) 2 pt 24 see comments
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Avoid drift and tailwater runoff into surface waters. Do not make more than two postharvest applications during the fern stage. Use allowed under a Supplemental Label.
 
D. METHOMYL*
  (Lannate) LV 1.5–3 pt 48 1
  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.
 
E. 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.
 
F. CARBARYL
  (Sevin) Bait 5% 30–40 lb 12 l
  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. Do not apply more than 20 lb/acre to spears.
 
G. 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 (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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 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). For additional information, see their Web site at http://www.irac-online.org/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Asparagus
UC ANR Publication 3435

Insects

  • E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Insects:
  • R. J. Mullen, UC Cooperative Extension, San Joaquin County
  • W. E. Chaney, UC Cooperative Extension, Monterey County
  • C. B. Fouche, UC Cooperative Extension, San Joaquin County

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