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UC Pest Management Guidelines


Beet armyworm larva.

Eggplant

Armyworm

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

(Reviewed 4/10, updated 4/10)

In this Guideline:


DESCRIPTION OF THE PESTS

In addition to eggplants, armyworms feeds on sugarbeet, alfalfa, beans, eggplants, tomatoes, and a variety of weeds such as lambsquarter, redroot pigweed, and nettleleaf goosefoot. During winter and spring, the population is concentrated on weeds, but in late spring moths begin laying eggs in host crops when the plants are young. Eggs tend to be laid on fully expanded young leaves. Newly hatched larvae feed together near the egg cluster and gradually disperse as they grow.

Beet armyworm. Adult beet armyworms are small, mottled-gray or dusky-winged moths. Females lay eggs in clusters on leaves; the clusters are covered with fluffy, dirty white scales. Eggs hatch in a few days and tiny caterpillars begin feeding while still clustered together on the plant. In 2 to 3 weeks beet armyworm larvae are full grown and about 1 inch long. The body is smooth with few hairs and predominantly green with mottled dark lines along the back. Just above the spiracle, lengthwise along the body, is a dark green to black line edged on each side with white. There is usually a small dark spot above the spiracle on the second pair of true legs.

Western yellowstriped armyworm. Larvae of the western yellowstriped armyworm are almost black, with two prominent and many fine, bright yellow stripes on the side. At maturity it is approximately 1.5 to 2 inches long. Eggs are laid in clusters on the upper side of leaves and covered with a gray, cottony material. Eggs hatch in a few days and larvae reach full size in 2 to 3 weeks. Larvae pupate on or just under the soil surface. Adults are brown moths that primarily fly at night but may be encountered flying up as you walk through the field. There are at least five generations per year in the low desert and four generations in the Central Valley. This pest may be abundant at any time from June to early September.

DAMAGE

Feeding by armyworms on the leaves, flowers, and fruit of eggplants can cause serious problems. As the fruit forms, armyworms may feed on calyx and can scar small fruit. Both defoliation and fruit loss result from the feeding.

MANAGEMENT

Regular monitoring of the leaves and fruit is important in detecting an infestation of armyworms.

Biological Control
Many natural enemies attack armyworms and prevent a large number of the population from reaching maturity. Among the most common parasites are the wasps Hyposoter exiguae and Chelonus insularis, and the tachinid fly Lespesia archippivora. Viral diseases may also be important; however, none of these organisms provide reliable control of armyworms when they feed on the fruit.

Organically Acceptable Methods
Biological control and sprays of Bacillus thuringiensis or the Entrust formulation of spinosad are acceptable for use on an organically certified crop.

Monitoring and Treatment Decisions
Sampling guidelines for armyworms in eggplants have not been developed. Look for the cream-colored egg mass or, later, for feeding on pigweed, nettleleaf goosefoot, and lambquarters plants in and around the field. If armyworms are present on these weeds, also examine the eggplants. Treat if foliar damage is occurring.

Common name Amount/Acre** R.E.I.+ P.H.I.+
(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 and impact on natural enemies and honey bees. When choosing a pesticide, also consider information relating to environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. SPINOSAD
  (Entrust)# 1.25–2.5 oz 4 1
  (Success) 4–8 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Use higher rate for larger worms and heavy infestations. Best control is achieved when aimed at newly hatched larvae and coverage is thorough. More broad-spectrum than Bt but has very low toxicity to humans, vertebrates, and the adults of many natural enemies. Can remain toxic to larval stages (especially syrphid fly) for 5-7 days after treatment. Do not exceed 29 fl oz of Success or 9 oz of Entrust/acre/crop.
 
B. BACILLUS THURINGIENSIS ssp. AIZAWAI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11
  COMMENTS: Bacillus thuringiensis preparations must be consumed by the larva to be effective; coverage is critical. Most effective when applied in spring when there is less foliage than later in season. Control decreases as worms mature and is most effective against newly hatched worms.
 
C. PERMETHRIN*
  (Pounce) 25WP 6.4–9.6 oz 12 3
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Depending on the time of year, can cause mite outbreaks. Best if used early in season (spring); avoid consecutive treatments.
 
D. METHOMYL*
  (Lannate SP) 0.25–0.5 lb 48 5
  (Lannate LV) 0.75–1.5 pt 48 5
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Depending on the time of year, can cause mite outbreaks. Best if used early in season (spring); avoid consecutive treatments.
 
E. ESFENVALERATE*
  (Asana XL) 5.8–9.6 fl oz 12 7
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Depending on the time of year, can cause mite outbreaks. Best if used early in season (spring); avoid consecutive treatments.
 
** 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: Eggplant
UC ANR Publication 3475
Insects and Mites
R. H. Molinar, UC Cooperative Extension Fresno County
J. L. Aguiar, UC Cooperative Extension Riverside County
M. J. Jimenez, UC Cooperative Extension Tulare County
P. B. Goodell, UC IPM, Kearney Agricultural Center, Parlier

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