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How to Manage Pests

UC Pest Management Guidelines

| More pests | More crops | About guidelines |

Western yellowstriped armyworm larva.

Cotton

Western Yellowstriped Armyworm

Scientific Name: Spodoptera praefica

(Reviewed 1/08, updated 1/08)

In this Guideline:

DESCRIPTION OF THE PEST

Western yellowstriped armyworm larvae are dark colored, usually nearly black (but occasionally gray) with a broad yellow stripe on each side. They have a black spot on the side of the first abdominal segment.

DAMAGE

If infestations occur early in the season, young cotton plants may be defoliated, but this is rare. Later season infestations occur primarily on field edges and can cause defoliation and damage to fruit.

MANAGEMENT

This pest occurs infrequently in the San Joaquin Valley. It is a foliage feeder that may become abundant during the late season as a result of migration from nearby alfalfa. You can stop migrating larvae by plowing a trench with the steep side toward cotton and applying an insecticidal spray to kill trapped larvae. Treat only the infested area; it is rarely necessary to treat a whole cotton field.

Organically Acceptable Methods
Sprays of Bacillus thuringiensis are acceptable for use on organically grown cotton.

Monitoring and Treatment Decisions
The degree of foliage damage is the best indicator for determining treatment thresholds. Early in the season, plants can sustain up to 50% loss of leaf surface without affecting yield. During the fruiting period, only 20 to 25% of the leaf surface can be lost without yield loss. After this period, up to 50% loss of leaf surface can again be tolerated.

Common Name Amount/Acre** R.E.I.+ P.H.I.+
(trade name)   (hours) (days)
The following materials are listed in order of usefulness in an IPM program, taking into account efficacy, selectivity, persistence, and impact on 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. BACILLUS THURINGIENSIS ssp. KURSTAKI#
  (various products) Label rates 4 0
  SELECTIVITY: High
  PERSISTENCE: Pest–Short; Natural Enemies–Short
  MODE OF ACTION GROUP NUMBER1: 11.B2
  COMMENTS: Does not disrupt natural enemies.
   
B. METHOXYFENOZIDE
  (Intrepid) 2F Label rates 4 14
  SELECTIVITY: High
  PERSISTENCE: Pest–Moderate; Natural Enemies–Moderate
  MODE OF ACTION GROUP NUMBER1: 18A
  COMMENTS: An insect growth regulator.
 
C. INDOXACARB
  (Steward) Label rates 12 14
  SELECTIVITY: Moderate
  PERSISTENCE: Pest–Moderate; Natural Enemies–Moderate
  MODE OF ACTION GROUP NUMBER1: 22
   
D. ACEPHATE
  (Orthene) 75S 1.33 lb 24 21
  SELECTIVITY: Low
  PERSISTENCE: Pest–Moderate; Natural Enemies–Moderate
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: May cause severe spider mite infestations.
 
E. METHOMYL*
  (Lannate) SP 0.5–0.75 lb 72 15
  SELECTIVITY: Low
  PERSISTENCE: Pest–Short; Natural Enemies–Short
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Kills eggs and larvae. Use may redden cotton; do not make more than 2 applications/season. Do not graze or feed cotton trash to livestock.
 
**  Mix with sufficient water to provide complete coverage.
+ Preharvest interval. Do not apply within this many days of harvest.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically produced cotton.
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: Cotton
UC ANR Publication 3444
Insects and Mites
L. D. Godfrey, Entomology, UC Davis
P. B. Goodell, UC IPM Program/ Kearney Agricultural Center, Parlier
E. T. Natwick, UC Cooperative Extension, Imperial County
D. R. Haviland, UC IPM Program, Kern County
Acknowledgment for contributions to Insects and Mites:
E. E. Grafton-Cardwell, Kearney Agricultural Center, Parlier
N. C. Toscano, Entomology, UC Riverside

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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