How to Manage Pests

UC Pest Management Guidelines



Scientific names:
Western yellowstriped armyworm: Spodoptera praefica
Yellowstriped armyworm: S. ornithogalli

(Reviewed 12/09, updated 11/12)

In this Guideline:


Western yellowstriped armyworm

Adult moths of the western yellowstriped armyworm are difficult to distinguish from other nocturnal moths. Females lay eggs in clusters covered with a gray, cottony material. Larvae measure about 1.5 inches (3.8 cm) long when fully grown. They are usually black with one prominent stripe over many narrow bright ones on each side of its body. The head is brown with a netted pattern. There is also a large black spot above the first abdominal spiracle.

Yellowstriped armyworm

Larvae of the yellowstriped armyworm are almost black, with two prominent and many fine, bright yellow stripes on the side.


Primarily foliage feeders, armyworms will also attack fruit, creating single or closely grouped circular or irregular holes on the surface. In many cases, feeding is superficial and little loss would result if not for decay organisms that enter wounds and rot fruit. Young armyworms skeletonize leaves; older larvae chew holes. Problems caused by the western yellowstriped armyworm may occur if peppers are planted near alfalfa or bean fields. The yellowstriped armyworm does not enter the fruit and infestations are most severe from July to mid-September.


Yellowstriped armyworm is not a serious pest every year, but is very destructive on occasion. Armyworms tend to build up in alfalfa and weedy areas around the field and migrate from these areas when cut. Armyworms only need to be controlled if they are feeding on the crop. Keep crop residue and weeds in field and surrounding areas to a minimum to lessen the attraction of the field.

Armyworms migrating into a field can be deterred by digging a trench or by a strip treatment of an insecticide on the perimeter of the field.

Biological Control

Many natural enemies attack armyworms. Among the most common parasites are the wasps, Hyposoter exiguae and Chelonus insularis, and the tachinid fly, Lespesia archippivora. Armyworms can easily be checked for the presence of Hyposoter exiguae by pulling the larva apart and looking for the parasite larvae. Viral diseases also kill significant numbers.

Cultural Control

A deep trench can be plowed around the edges of the field with the steep side toward the peppers. This will often prevent movement of armyworm larvae into the crop.

Organically Acceptable Methods

Cultural controls and sprays of Bacillus thuringiensis or the Entrust formulation of spinosad are acceptable for use on an organically certified crop.

Monitoring and Treatment Decisions

If larvae are migrating to peppers from nearby fields and a trench can not be dug, treatment may be warranted. Treating only the field border may be effective.

Common name Amount per 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. When choosing a pesticide, consider information relating to impact on natural enemies and pollinators and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
  (Coragen) 3.5-5 fl oz 4 1
  (Avaunt) 3.5 oz 12 3
  COMMENTS: Minimum interval between sprays is 5 days. Do not apply more than 14 oz/acre per crop.
  (Intrepid) Label rates 4 1
  COMMENTS: An insect growth regulator. Apply at the beginning of egg hatch. Pheromone traps can be used to detect moth flight. When traps indicate a flight is occurring, monitor plants for eggs and treat when they appear. Do not apply more than 16 fl oz/acre per application or 64 fl oz/acre per season.
  (various products) Label rates 4 0
  COMMENTS:Bacillus thuringiensis preparations must be consumed by the larva to be effective. Coverage is critical for controlling this pest, especially between and under leaves and where leaves touch the fruit.
  (Kryocide) 8-12 lb 12 14
** 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.
# 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



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Peppers
UC ANR Publication 3460

Insects and Mites

E. T. Natwick, UC Cooperative Extension, Imperial County
J. T. Trumble, Entomology, UC Riverside
Jose Aguiar, UC Cooperative Extension, Riverside County
Acknowledgment for contributions to Insects and Mites:
W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
R. L. Coviello, UC Cooperative Extension, Fresno County
C. G. Summers, Kearney Agricultural Center, Parlier
W. E. Chaney, UC Cooperative Extension, Monterey County
C. F. Fouche, UC Cooperative Extension, San Joaquin County

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