UC Management Guidelines for Yellowstriped Armyworm on Cucurbits

UC Pest Management Guidelines

Adults of (left top to bottom) variegated cutworm, beet armyworm, cabbage lopper, (right top to bottom) tomato fruitworm (=corn earworm, cotton bollworm), tobacco budworm, western yellow striped armyworm.

Cucurbits

Yellowstriped Armyworm

Scientific Name: Spodoptera ornithogalli

(Reviewed 11/05, updated 6/08)

In this Guideline:

Description of the pest
Damage
Management

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

Yellowstriped armyworm eats both foliage and fruit. It does not enter the fruit, but feeds on the surface, causing irregular holes. Infestations are most severe from July to mid-September.

This insect is not a serious pest every year but is very destructive on occasion. Infestations originate from moths or caterpillars that migrate from alfalfa fields when the alfalfa is cut. Cleaning up crop residue and weeds in field and surrounding areas may lessen attraction of the field to the pest.

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. Yellowstriped armyworm 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.

Organically Acceptable Methods
Sanitation in the field and surrounding areas along with cultural control and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable to use in an organically certified crop.

Monitoring and Treatment Decisions
If young instars (or stages) of the yellowstriped armyworm are found on foliage during routine field inspections, consider treating with a low impact product such as Bacillus thuringiensis, methoxyfenozide (Intrepid), or spinosad (Entrust). For older stages of this armyworm, use methomyl.

Common name

Amount/Acre

R.E.I.+

P.H.I.+

(trade name)

(hours)

(days)

When choosing a pesticide, consider information relating to water quality and impact on natural enemies and honey bees.

METHOXYFENOZIDE

(Intrepid) 2F

4–10 fl oz

MODE OF ACTION GROUP NUMBER¹: 18A

COMMENTS: Use allowed under a supplemental label.

BACILLUS THURINGIENSIS ssp. AIZAWAI#

(various products)

Label rates

MODE OF ACTION GROUP NUMBER¹: 11.B1

COMMENTS: Bacillus thuringiensis may be used to control small armyworms (first and second instar) when populations are light and full coverage sprays are applied. Repeat treatment as necessary. If mature larvae or heavy populations are present, use one of the other materials listed.

METHOMYL*

(Lannate) 90

0.5–1.0 lb

1 (0.5 lb or less)

3 (more than 0.5 lb)

(Lannate) LV

1.5–3 pt

1 (1.5 pt or less)

3 (more than 1.5 pt)

MODE OF ACTION GROUP NUMBER¹: 1A

COMMENTS: For use on cucumbers, melons, and summer squash.

SPINOSAD

(Entrust)#

1.25–2.5 oz

1-cucumbers
3–other cucurbits

MODE OF ACTION GROUP NUMBER¹: 5

COMMENTS: Not as effective on yellowstriped armyworms as other insecticides listed. Apply to small armyworms (first and second instars). Time spray to target eggs at hatch or small larvae. Do not apply more than 9 oz Entrust/acre/season.

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.

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/.

Acceptable for use on organically grown produce.

Permit required from county agricultural commissioner for purchase or use.

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445
Insects and Mites
E. T. Natwick, UC Cooperative Extension, Imperial County
L. D. Godfrey, Entomology, UC Davis
C. G. Summers, Entomology, UC Davis/Kearney Agricultural Center, Parlier
J. J. Stapleton, UC IPM Program, Kearney Agricultultural Center, Parlier
Acknowledgment for contributions to Insects and Mites:
R. L. Coviello, UC Cooperative Extension, Fresno County
C. B. Fouche, UC Cooperative Extension, San Joaquin County
J. B. LeBoeuf, AgriData Sensing, Inc., Fresno
M. Murray, UC Cooperative Extension, Colusa/Glenn counties

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How to Manage Pests

UC Pest Management Guidelines

Cucurbits

Yellowstriped Armyworm

Scientific Name: Spodoptera ornithogalli

DESCRIPTION OF THE PEST

DAMAGE

MANAGEMENT

PUBLICATION