How to Manage Pests

UC Pest Management Guidelines

Lettuce

Lygus Bug (Western Tarnished Plant Bug)

Scientific Name: Lygus hesperus

(Reviewed 4/17, updated 4/17)

In this Guideline:


DESCRIPTION OF THE PEST

Western tarnished plant bug is commonly referred to as lygus bug. Adults are small (about 0.25 inch), variably colored yellowish to green to bronze true bugs with a distinctive triangular marking on the back and wings composed of both membranous and hardened sections that are carried folded over the back. The mouthparts are needlelike and long in relation to the body size.

Eggs are laid in plant tissue. Immature lygus bugs are light green and resemble adults in shape but lack wings. First and second instar nymphs can be confused with aphids when casually observed, but lack cornicles and move much faster. Second and third instars have a dark spot on the abdomen. Four additional spots can be seen on the thoracic segments of fourth and fifth instars. In general, later instars can be recognized by their developing wing pads.

DAMAGE

Lygus feeds by piercing cell membranes. This activity affects the subsequent cell division in the area of feeding resulting in sunken, callused lesions that could become necrotic with time. Egg laying injury is also associated with lesions. Adults lay eggs in the midrib areas of the leaf. The injury initially appears as holes or pits on the midrib and later expands into lesions.

MANAGEMENT

Biological Control

Various species of natural enemies attack different life stages of the lygus bug. Egg parasitoid, Anaphes iole, nymphal parasitoid, Peristenus relictus, and predatory arthropods that include bigeyed bugs (Geocoris spp.), damsel bugs (Nabis spp.), minute pirate bugs (Orius tristicolor), and several species of spiders provide partial control of the western tarnished plant bug. Entomopathogenic fungi, Beauveria bassiana, Isaria fumosorosea, and Metarhizium brunneum can also be used to control adults and nymphs.

Cultural Control

Manage weeds around the fields to suppress western tarnished plant bug numbers. Protect populations of natural enemies.

Organically Acceptable Methods

Use biological and cultural controls on organically certified crop. Entomopathogenic fungi, Beauvaria bassiana (e.g. BotaniGard, Mycotrol ESO) or Isaria fumosorosea (PFR-97), are available for all growth stages. Use azadirachtin (e.g. AzaGuard) for control of nymphs.

Monitoring and Treatment Decisions

Lygus bugs frequently move into crop fields in spring when weeds and native vegetation dry down. Consequently, large numbers of bugs can move into celery fields in a short period of time. Determining the level of lygus bug infestation is difficult because the insects are cryptic (hiding) and their activity cycle during any day varies greatly. Lygus bugs become inactive and secretive during temperature extremes and windy conditions.

Because of the severity of the damage to lettuce, the threshold, while not specifically established, is very low. Sweep nets and detection of adults flying out of the crop when walking through the field, are the only ways to check for the presence of lygus bug. Sticky traps are not useful for monitoring this pest.

Common name Amount per acre** REI‡ PHI‡
(Example trade name)   (hours) (days)
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
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, 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. PERMETHRIN*
  (Ambush, Pounce 25WP) Label rates 12 1
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: Do not apply more than 2 lb a.i./acre per season. Do not use if leafminers are present.
 
B. MALATHION
  (Malathion 8) 1.88 pt 24 14
  MODE-OF-ACTION GROUP NUMBER1: 1B
  COMMENTS:
 
C. METHOMYL*
  (Lannate LV) 1.5–3 pt 48 7
  MODE-OF-ACTION GROUP NUMBER1: 1A
  COMMENTS: This active ingredient is very disruptive to parasites and predators. If caterpillars must also be controlled, it can be used to control Western tarnished plant bug; otherwise its use is not recommended. Do not apply more than 7.2 lb a.i./acre per crop.
 
D. ZETA-CYPERMETHRIN*
  (Mustang) 3.4–4.3 fl oz 12 1
  MODE-OF-ACTION GROUP NUMBER1: 3A
  COMMENTS: For use on head lettuce only. Do not use if leafminers are present.
 
E. AZADIRACHTIN#
  (AzaGuard) 1 pt 4 0
  (Neemix) 4.5% 4–7 oz 12 0
  MODE-OF-ACTION GROUP NUMBER1: Unknown
  COMMENTS: Always check with certifier if the material is permissible in organic production.
 
F. BEAUVARIA BASSIANA GHA
  (Mycotrol ESO)# 0.5–2 qt/100 gallons 4 0
  MODE-OF-ACTION GROUP NUMBER1: biological
  COMMENTS: In Canada, bees are often used to deliver the product to plants; nevertheless, it is potentially pathogenic to bees and most other insects.
 
G. Isaria fumosorosea
  (PFR-97 20% WDG)# 1–2 lb 4 0
  MODE-OF-ACTION GROUP NUMBER1: –
 
** Mix with sufficient water to obtain full coverage.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) 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 Modes of action are important in preventing the development of resistance to pesticides. 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. 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 is assigned by IRAC (Insecticide Resistance Action Committee).

[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
S. V. Joseph, UC Cooperative Extension, Monterey County
S. K. Dara, UC Cooperative Extension, Santa Barbara County

Acknowledgment for contributions to Insects and Mites:
N. C. Toscano, Entomology, UC Riverside

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