How to Manage Pests

UC Pest Management Guidelines

Eggplant

Armyworm

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

(Reviewed 4/10, updated 4/10, pesticides updated 5/16)

In this Guideline:


Description of the Pest

In addition to eggplants, armyworms feed on sugarbeet, alfalfa, beans, eggplants, tomatoes, and a variety of weeds such as lambsquarters, 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 lambsquarters 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 per acre** REI‡ PHI‡
(Example trade name)   (hours) (days)

UPDATED: 5/16
Calculate impact of pesticide on air quality
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. Not all registered pesticides are listed. Always read the label of the 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 Bacillus thuringiensis 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 to 7 days after treatment. Do not exceed 29 fl oz of Success or 9 oz of Entrust/acre per crop. Toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
B. BACILLUS THURINGIENSIS ssp. AIZAWAI#
  (various products) Label rates 4 0
  MODE-OF-ACTION GROUP NUMBER1: 11A
  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. FLUBENDIAMIDE
  (Belt SC) 1.5 fl oz 12 1
  MODE-OF-ACTION GROUP NUMBER1: 28
 
D. METHOXYFENOZIDE
  (Intrepid 2F) See label 4 1
  MODE-OF-ACTION GROUP NUMBER1: 18
 
E. TEBUFENOZIDE
  (Confirm) See label 4 7
  MODE-OF-ACTION GROUP NUMBER1: 18
  COMMENTS:
 
F. NOVALURON
  (Rimon) 9–12 fl oz 12 1
  MODE-OF-ACTION GROUP NUMBER1: 15
 
G. PERMETHRIN
  (Pounce 25WP)* 6.4–9.6 oz 12 3
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Depending on the time of year, can cause mite outbreaks. Best if used early in season (spring); avoid consecutive treatments. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
H. METHOMYL
  (Lannate SP)* 0.5–1 lb 48 5
  (Lannate LV)* 1.5–3 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. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.
 
I. ESFENVALERATE
  (Asana XL)* 5.8–9.6 fl oz 12 7
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Depending on the time of year, can cause mite outbreaks. Best if used early in season (spring); avoid consecutive treatments. Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging.

** 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 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).

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Eggplant
UC ANR Publication 3475

Insects and Mites

J. L. Aguiar, UC Cooperative Extension, Riverside County
M. J. Jimenez, UC Cooperative Extension, Tulare County
P. B. Goodell, UC IPM, Kearney Agricultural Research and Extension Center, Parlier

Acknowledgments for contributions to Insects and Mites:
R. H. Molinar, UC Cooperative Extension, Fresno County

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