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How to Manage Pests

UC Pest Management Guidelines


Cabbage looper larva.

Lettuce

Loopers

Scientific Names:
Cabbage looper: Trichoplusia ni
Alfalfa looper: Autographa californica

(Reviewed 8/07, updated 10/09)

In this Guideline:


DESCRIPTION OF THE PESTS

Loopers arch their backs as they crawl. Cabbage loopers usually have a narrow, white stripe along each side and several narrow lines down the back. Eggs are dome-shaped, and laid on the undersurfaces of older leaves. Adult moths have brown, mottled forewings marked in the center with a small silver figure 8.

DAMAGE

Young larvae feed primarily on the undersides of lower leaves, skeletonizing them. High populations can damage seedlings severely enough to kill them or slow growth enough to inhibit uniform maturing of the crop. Older larvae may burrow into the head from the top.

MANAGEMENT

Biological Control
Loopers have many natural enemies that often keep populations below economic thresholds. Maximize the use of these natural enemies by limiting treatments, especially between thinning and heading. In some areas an important biological control agent is a nuclear polyhedrosis virus that occurs naturally in the field. Bodies of loopers killed by the virus are dark, soft, and shapeless with their body contents often spilling onto the leaves.

Another important natural enemy in southern California, the tiny parasitic wasp, Trichogramma pretiosum, attacks looper eggs and eggs of certain other caterpillars. Eggs parasitized by Trichogramma turn black as the parasite matures inside and are easy to distinguish from normal eggs that remain white except for a black spot that appears just before hatching. Other parasites that attack looper caterpillars include the tachinid fly, Voria ruralis, and three wasps, Hyposoter exiguae, Copidosoma truncatellum, and Microplitis brassicae.

Organically Acceptable Methods
Biological control and sprays of Bacillus thuringiensis. and the Entrust formulation of spinosad are acceptable for use on organically certified crops, but spinosad is very detrimental to populations of syrphid flies.

Monitoring and Treatment Decisions
Look for signs of looper feeding: plants with holes in outer leaves, feces, caterpillars feeding on edge of hole. Check fields twice a week once seedlings emerge. Loopers, cabbageworms, armyworms, corn earworms, tobacco budworms, cutworms, and other caterpillars that feed on leaves and heads of lettuce can be assessed together, but species identification is important in choosing an insecticide.

Check at least 25 plants for caterpillars in each quadrant of a 40- to 80-acre field twice a week. Fields smaller than 40 acres may require fewer samples. In fields where the crop is heading, stop at five different locations in each quadrant and sample five plants at each location.

Treat seedlings or small plants if populations of medium-sized to large loopers are large enough to stunt growth. Treat well-established plants only if you find an average of more than one-half larvae per plant. For cabbage looper control, the best time to apply insecticide is in the afternoon.

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 the impact on natural enemies and honey bees and environmental impact. Not all registered pesticides are listed. Always read label of product being used.
 
A. BACILLUS THURINGIENSIS ssp. AIZAWAI#
  (various products) Label rates 4 0
  MODE OF ACTION GROUP NUMBER1: 11.B1
  COMMENTS: Not harmful to natural enemies.
 
B. CHLORANTRANILIPROLE
  (Coragen) 3.5–5 fl oz 4 1
  MODE OF ACTION GROUP NUMBER1: 28
 
C. ACEPHATE
  (Orthene 75 SP) 0.66–1.33 lb 24 21
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: Use on head lettuce only. Do not apply after first head begins to form. Do not apply more than 2.66 lb/season. Do not feed to livestock or allow animals to graze on treated areas. This material will also control aphids.
 
D. PERMETHRIN*
  (Pounce 3.2 EC) 4–8 oz 12 1
  (Pounce 25W) 6.4–12.8 oz 12 1
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Apply a minimum of 5 gal finished spray/acre by aircraft, 15 gal/acre with ground equipment. Do not use if leafminers are present.
  . . . or . . .
  (Ambush 25WP) 6.4–12.8 oz 12 1
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Do not apply more than 2 lb a.i./acre/season. Do not graze treated areas or feed crop refuse to livestock. Do not use if leafminers are present.
 
E. ZETA-CYPERMETHRIN*
  (Mustang 1.5EW) 3.41–4.26 oz 12 1
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Do not exceed 0.3 lb a.i./acre/season. Do not use if leafminers are present. For use on head lettuce only.
 
F. METHOMYL*
  (Lannate SP) 0.25–1 lb 48 0.25–0.5 lb: 7
  over 0.5 lb: 10
  . . . or . . .
  (Lannate LV) 0.75–3 pt 48 0.75–1.5 pt: 7
  over 1.5 pt: 10
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Will also give fair control of aphids. Do not use if leafminers are present. Caused leaf area reductions of nearly 38% in seedlings of the Mesa variety.
 
G. SPINOSAD
  (Entrust)# 1–2 oz 4 1
  (Success) 4–8 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 5
  COMMENTS: Not recommended when lettuce aphid is present because of its negative impact on syrphid fly larvae.
 
H. METHOXYFENOZIDE
  (Intrepid 2F) 4–8 oz 4 1
  MODE OF ACTION GROUP NUMBER1: 18A
 
I. THIODICARB*
  (Larvin 3.2) Label rates 48 14
  MODE OF ACTION GROUP NUMBER1: 1A
  COMMENTS: Do not use if leafminers are present.
 
J. INDOXACARB
  (Avaunt) 3.5 oz 12 3
  MODE OF ACTION GROUP NUMBER1: 22
  COMMENTS: Use to control low level populations.
 
K. EMAMECTIN BENZOATE*
  (Proclaim) 2.4–4.8 oz 12 7
  MODE OF ACTION GROUP NUMBER1: 6
 
** Mix with enough water to provide complete coverage.
+ 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.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for 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/.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Lettuce
UC ANR Publication 3450
Insects and Other Arthropods
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Insects and Mites:
W. E. Chaney, UC Cooperative Extension, Monterey County
N. C. Toscano, Entomology, UC Riverside

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