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How to Manage Pests

UC Pest Management Guidelines

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Dry Beans

Lygus Bugs

Scientific Names: Lygus hesperus, Lygus elisus

(Reviewed 8/07, updated 8/07)

In this Guideline:

Description of the pests
Damage
Management

DESCRIPTION OF THE PESTS

The lygus bug adult is approximately 0.25 inch long and about half as wide. It is generally brownish, but varies from green to straw-colored, to tawny to 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 bugs feeding on young, developing seed pods cause pitting and 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, Anaphesiole. Generalist 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. Leaving areas of uncut alfalfa within or near the harvested area may reduce the movement of lygus into neighboring fields, including dry beans.

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).

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

Monitoring and Treatment Decisions
Start sampling during the bud stage. Check fields twice weekly. 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.
Pinks, California Reds: 1.0 to 1.5 bugs per sweep.
Small Whites: 1.5 bugs per sweep.
Green Limas: 1.0 bug 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)

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

LAMBDA-CYHALOTHRIN*

(Warrior with Zeon)

2.56–3.84 oz

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.

ZETA-CYPERMETHRIN*

(Mustang)

3–4.3 oz

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.

DIMETHOATE

2.67 lb/gal EC

1.5 pt

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.

ACEPHATE

(Orthene) 75 SP

0.67 lb

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/.

PUBLICATION

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 Co.

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