How to Manage Pests

UC Pest Management Guidelines

Cotton

Western Yellowstriped Armyworm

Scientific Name: Spodoptera praefica

(Reviewed 5/13, updated 5/13)

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 (Bt) 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 per acre**	R.E.I.‡	P.H.I.‡
(example trade name)			(hours)	(days)
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, also 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.	BACILLUS THURINGIENSIS ssp. KURSTAKI#
	(various products)	Label rates	4	0
	SELECTIVITY: High
	PERSISTENCE: Pest: Short NE:2 Short
	MODE OF ACTION GROUP NUMBER1: 11
	COMMENTS: Does not disrupt natural enemies.
B.	CHLORANTRANILIPROLE
	(Coragen)	3.5–7.0 fl oz	4	21
	SELECTIVITY: High
	PERSISTENCE: Pest: Unknown NE:2 Short
	MODE OF ACTION GROUP NUMBER1: 28
C.	FLUBENDIAMIDE
	(Belt SC)	2–3 fl oz	12	28
	SELECTIVITY: High
	PERSISTENCE: unknown
	MODE OF ACTION GROUP NUMBER1: 28
	COMMENTS: A newer material; impact on beneficials not yet determined. Highly toxic to honey bees.
D.	METHOXYFENOZIDE
	(Intrepid 2F)	Label rates	4	14
	SELECTIVITY: High
	PERSISTENCE: Pest: Moderate NE:2 Moderate
	MODE OF ACTION GROUP NUMBER1: 18
	COMMENTS: An insect growth regulator.
E.	INDOXACARB
	(Steward)	Label rates	12	14
	SELECTIVITY: Moderate
	PERSISTENCE: Pest: Moderate NE:2 Moderate
	MODE OF ACTION GROUP NUMBER1: 22A
F.	ACEPHATE
	(Orthene 97)	1 lb	24	21
	SELECTIVITY: Low
	PERSISTENCE: Pest: Moderate NE:2 Moderate
	MODE OF ACTION GROUP NUMBER1: 1B
	COMMENTS: May cause severe spider mite infestations.
G.	METHOMYL*
	(Lannate SP)	0.5 lb	72	15
	SELECTIVITY: Low
	PERSISTENCE: Pest: Short NE:2 Short
	MODE OF ACTION GROUP NUMBER1: 1A
	COMMENTS: Kills eggs and larvae. Use may redden cotton. According to the label, do not make more than 8 applications per 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/.
2	NE = natural enemies

PUBLICATION

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 and Kearney Agricultural Research and Extension Center, Parlier
• E. T. Natwick, UC Cooperative Extension - Desert Research and Extension Center, Imperial County
• D.R. Haviland, UC Cooperative Extension, Kern County and UC IPM Program

Acknowledgment for contributions to Insects and Mites:

• E. E. Grafton-Cardwell, Kearney Agricultural Research and Extension Center, Parlier
• N. C. Toscano, Entomology, UC Riverside

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