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How to Manage Pests

UC Pest Management Guidelines


Adult lygus bug, Lygus hesperus.

Dry Beans

Lygus Bugs

Scientific Names: Lygus hesperus, Lygus elisus

(Reviewed 8/07, updated 12/08)

In this Guideline:


DESCRIPTION OF THE PESTS

The lygus bug adult is about 0.25 inch long and about half as wide. It is generally brownish but varies from green to straw-colored, tawny, or light brown; the body is marked with a pattern of different shades of brown and occasionally yellow or red marks. A prominent V-shaped yellowish area is near the center of the body at the base of the wings.

Lygus eggs are laid within plant tissue so that only the oval-shaped cap is visible. These eggs are hard to locate, even with the use of a hand lens. Active green nymphs hatch from the eggs. Red coloration on the tips of the antennae helps to distinguish early instar Lygus from aphids. Older nymphs may be recognized by distinct wing pads and by the five black dots on their backs, two on the first and second segments of the thorax and one in the center of the abdomen.

DAMAGE

Lygus bugs may be present throughout the growing season and can be highly destructive to a bean crop. They have sucking mouthparts with which they pierce and consume plant tissue. The type of damage varies with plant age. During early bud and flowering stages, lygus bugs cause bud and flower loss resulting in reduced yields. Lygus bug feeding on young, developing seed pods causes pod distortion, pitting, blemishes on table market beans, and reduce germination in seed beans.

MANAGEMENT

Biological Control
Lygus bug eggs are often parasitized and killed by a small parasitic wasp, Anaphes iole. General predators, such as lacewings and damsel bugs, may prey on lygus bug nymphs. Minimizing the use of broad-spectrum insecticides will help conserve these natural enemies.

Cultural Control
Lygus are likely to move when weeds such as pigweed, wild radish, and mustard dry and become unsuitable. Lygus are also known to migrate from newly cut alfalfa fields and safflower fields to nearby crops, where they cause considerable damage.

As a preferred host, alfalfa hay might be managed to suppress movement of lygus into dry bean fields by staggering cuttings to preserve habitat. Leave a small, uncut strip at each harvest to help limit the movement of lygus bugs into neighboring beans. The use of habitat preservation does not work as well in beans as in cotton because lygus prefers legumes as a habitat. However, alfalfa strips also serve as reservoirs for predators and parasites that will eventually move into beans and help suppress spider mites, lygus bugs, and caterpillars. If considering the use of alfalfa habitat preservation (strip or staggered cutting), be aware of the potential for quick movement and establishment in beans by lygus.

Overall Strategy
Maintain nearby alfalfa fields in a succulent condition.

  • Avoid cutting all alfalfa fields in an area within a short time period. Leave an uncut strip or check at each cutting along the border between alfalfa and beans to slow lygus bug migration.
  • If lygus bug populations get very high, uncut strips of alfalfa may be treated with an insecticide if needed, but sprays should be avoided where possible to protect beneficials.
  • Where strips of alfalfa grow within or along edges of the bean field:
    • Plant a sufficient area with alfalfa, manage for succulent growth, and alternate cutting half of each strip every two weeks.
    • Cut back alfalfa stems with a stalk cutter. In a 28-day cycle, many lygus bug eggs will be inside the cut stems and will die as the stems desiccate.

Lygus populations can impact vine and bush varieties of baby and large limas differently. In research trials, bush variety Luna showed better lygus tolerance and higher yields than other varieties. Yields were not affected up to 1.5 lygus/sweep with Luna variety at the bud through flowering stage. (This variety does not have nematode resistance, however, and should not be used in fields with a history of nematode populations). Baby lima varieties UC 302 and UC 279 look promising in resistance to lygus bug but have not yet been released.

Organically Acceptable Methods
Biological and cultural control are organically acceptable methods.

Monitoring and Treatment Decisions
Start sampling during the bud stage and continue through pod fill. Check fields twice weekly. Record observations on a monitoring form (117 KB, PDF). Determine lygus bug numbers (adults and nymphs) by using the standard insect sweep net. Take a series of five to ten 180° sweeps in four to six areas of the field. Pass the net through the top of two rows of bean plants (one bed for double row plantings or two beds for single row plantings). Treatment thresholds are available for bean yield; however, these thresholds may not reflect losses in bean quality. Treatment thresholds are:

  • Blackeyes: 0.5 lygus bug per sweep during bud through small pod stage; 1.0 bug per sweep later in season.
  • Baby Limas: Luna variety 1.0 to 1.5 lygus per sweep from bloom to flowering; 1.5 to 2.0 per sweep later in season.
  • Limas, all other varieties: 0.5 lygus bug per sweep during early bloom; 1.0 to 2.0 bugs per sweep later in season.
  • Common beans: 1.0 to 1.5 bugs per sweep.

Note: Determining lygus populations in vine type varieties is difficult because of the large amount of plant biomass that makes it impossible to penetrate into the canopy with a sweep net. Pulling the canopy apart and visually inspecting for lygus activity is highly recommended along with sweeping. Mid-morning evaluations are more accurate than afternoon evaluations because hot temperatures cause lygus to retreat into the lower sections of the canopy.

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.
 
A. LAMBDA-CYHALOTHRIN*
  (Warrior with Zeon) 2.56–3.84 oz 24 see comment
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Do not apply more than 0.96 pt/acre/season. Has some mite suppressive activity but may not prevent an outbreak. Preharvest interval (P.H.I.) is 7 days for succulent shelled or edible podded crops and 21 days for dried shelled crops.
 
B. ZETA-CYPERMETHRIN*
  (Mustang) 3–4.3 oz 12 see comment
  MODE OF ACTION GROUP NUMBER1: 3
  COMMENTS: Can cause outbreaks of bean aphid and mites. Tank mix with dimethoate if bean aphid is present. If mites are present, consider a tank mix with dicofol (Kelthane). (For all tank mixes, observe all directions for use on both labels, and employ the most restrictive limits and precautions.) Do not apply more than 0.3 lb a.i./acre/season. Preharvest interval (P.H.I.) is 1 day for succulent shelled or edible podded crops and 21 days for dried shelled crops.
 
C. DIMETHOATE
  2.67 lb/gal EC 1.5 pt 48 0
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: May result in mite outbreak. Highly toxic to honey bees; do not apply when bees are present. Ground or air application. Do not feed treated vines to livestock. Lygus bug populations may be resistant to dimethoate in some areas.
   
D. ACEPHATE      
  (Orthene) 75 SP 0.67 lb 24 14
  MODE OF ACTION GROUP NUMBER1: 1B
  COMMENTS: May result in mite outbreaks. Highly toxic to honey bees; do not apply when bees are present. Ground or air application. Do not feed treated vines to livestock.
 
** Mix with sufficient water to obtain full 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.
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/.

IMPORTANT LINKS

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446
Insects and Mites
L. D. Godfrey, Entomology, UC Davis
R. F. Long, UC Cooperative Extension, Yolo County

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