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UC Pest Management Guidelines


Beet armyworm larva.

Celery

Beet Armyworm

Scientific Name: Spodoptera exigua

(Reviewed 10/05, updated 6/08)

In this Guideline:


DESCRIPTION OF THE PEST

Beet armyworm adults are 0.5 to 0.75 inch, nondescript brown moths. They typically lay masses of 20 to 120 eggs and cover them with light-colored scales, which gives the egg masses a distinctive cottony appearance. Up to 400 or more eggs can be laid by each female. The early instar larvae are a pale green and often feed gregariously for the first few days. Larger larvae range from green to black, and often have a broad stripe along each side of the body. The larger larvae feed singly. The larval stages last from 2.5 to 3 weeks at 70° to 80°F. Large larvae generally hide in the center of the plant or underground during most daylight hours. After five to six instars, the larvae burrow into the soil to pupate. The pupal stage persists 7 to 10 days but may be much longer at cooler temperatures. Although newly emerged adults can be found throughout the year in central and southern California, major emergences and migration flights are usually recorded in spring through late summer.

DAMAGE

Young worms feed on celery leaves but rarely cause substantial damage. However, larger larvae feed on petioles and cause significant crop loss. Large larvae are quite mobile and have been observed to travel over 10 feet per night, feeding on several plants. If petioles near the outside of the plants are damaged, they can be removed. If damage occurs in a centrally located petiole the plant must often be discarded.

MANAGEMENT

Biological Control
Many natural enemies attack beet armyworms. Among the most common parasites are the wasps, Hyposoter exiguae and Chelonus insularis, and the tachinid fly, Lespesia archippivora. Viral diseases also kill significant numbers.

Cultural Control
Disc fields immediately following harvest to remove the food source for any remaining larvae. Some pupae may be affected by discing as well.

Organically Acceptable Methods
Cultural and biological controls and sprays of Bacillus thuringiensis and the Entrust formulation of spinosad are acceptable for use on organically grown produce.

Monitoring and Treatment Decisions
Beet armyworm eggs and larvae are often easier to find on weeds in and near the field than in the celery plant. Weeds can be pulled and readily examined whereas celery is often brittle and easily damaged during the early morning and late evening hours when larvae are active. Chenopodium species (e.g., lambsquarters, goosefoot) appear to be particularly attractive to beet armyworm larvae. Populations can build rapidly, so check fields twice a week. Monitor adults with pheromone traps placed along the edges of fields. This is a particularly good technique for detecting large emergences or migrations occurring on weather fronts. Reliable treatment levels have not been established, but the presence of more than one large larva or five small larvae on 25 plants would be of concern. Make treatments when larvae are small; large larvae are more difficult to kill with compounds such as Bacillus thuringiensis. Because larvae become active at dusk, and sunlight degrades many pesticides, the best time for insecticide treatment is in the twilight evening hours.

Common name Amount/Acre R.E.I.+ P.H.I.+
(trade name)   (hours) (days)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to water quality and impact on natural enemies and bees. Not all registered pesticides are listed. Always read label of product being used.
 
A. SPINOSAD
  (Entrust)# 1.25-2.5 oz 4 1
  (Success) 4–8 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Apply as a foliar spray. Heavy infestations may require repeat applications but do not apply more than 3 times in any 21-day period or apply more than 6 treatments/crop. Provides some suppression of leafminer populations and has less of a negative impact on their natural enemies than other materials (except Bt) listed. Use allowed under a supplemental label.
 
B. SPINETORAM
  (Radiant) SC 5–10 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
 
C. METHOXYFENOZIDE
  (Intrepid) 2F Label rates 4 1
  MODE OF ACTION GROUP NUMBER1: 18A
  COMMENTS: An insect growth regulator. Do not apply more than 16 fl oz/acre/application or more than 64 oz/acre/season. See label for rotational crop restrictions.
 
D. METHOMYL*
  (Lannate LV) 0.75–1.5 pt 48 7
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Disruptive to parasites of lygus, leafminers, and aphids. If these pests are present, use of this material may result in outbreaks of these pests.
 
E. BACILLUS THURINGIENSIS# ssp. AIZAWAI
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B1
  COMMENTS: Apply when armyworms are small.
 
F. THIODICARB
  (Larvin) 3.2 16–30 fl oz 48 14
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Use higher rates for heavier infestations of larger larvae. Do not exceed 60 fl oz/acre/season. Disruptive of natural enemies.
 
+ 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 http://www.irac-online.org/.
* Permit required from county agricultural commissioner for purchase or use.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Celery
UC ANR Publication 3439
Insects
L. D. Godfrey, Entomology, UC Davis
J. T. Trumble, Entomology, UC Riverside
Acknowledgement for contributions to Insects:
W. E. Chaney, UC Cooperative Extension, Monterey County

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