Pests Affecting Native Plant Seed Production
Great Basin Native PlantsUncomphagre Plateau Project
Native Plant Fields


Lygus have impacted seed production in Hedysarum, Penstemon, Lupinus and many other forbs species. They should be anticipated as a seed production pest whenever forbs are produced near alfalfa hay. Alfalfa seed and cotton growers have many decades of experience with lygus control. They are an excellent information resource.

Lygus Bugs

Scientific Name: Hemiptera: Miridae: Lygus hesperus

Lygus bugs are a serious pest of many forbs grown for seed. Adult bugs are very mobile and have a very broad host range. They move into seed production fields during bloom and early seed set and feed on flowers and developing seed, aborting the seed.

Lygus have piercing and sucking mouthparts which they use to suck juices from the plants they feed on. They puncture plant tissue and suck juices. they can inject a toxin when they feed on buds. Severe Lygus infestations can cause loss of all of the flower buds within a field. Foliar feeding can cause stunted or irregular growth. Some species of Penstemon respond to Lygus feeding by producing a black tar-like substance.

Adult Adult Lygus are about 5 mm in length and about half as wide. Color varies with age, with newly molted bugs being green and older bugs brownish There is a distinct scutellum, a triangular light colored area behind the head. Adult lygus are winged although the wings remain folded over the abdomen when not in use. Lygus Bug Adult
Egg Eggs are inserted into plant tissue, usually in the top portion of a plant.  
Larva Immature lygus can be recognized by the presence of wing pads. There pads will vary in size by instar. Early instar nymphs can be mistaken for aphids. They are very mobile, much more than aphids. The first three instars are greenish, fourth and fifth have darker markings. Lygus Nymphs


Management of lygus must start outside of the seed production field. Lygus populations build in other crops, especially alfalfa hay and weeds such as kochia. When the hay is cut or weeds burned down with herbicide, the Lygus move into the blooming seed crop. If no action is taken, severe damage can occur. The obvious solution would be to kill the bugs before they move, but this is rarely possible. It is important to monitor seed fields for lygus. A sweep net is a quick, easy and inexpensive tool for monitoring fields. Control thresholds will vary with crop species, value, and timing of lygus infestation in relation to harvest. In general, with high value crops, counts of immature lygus that are higher than one per sweep and increasing over time can be a cause for concern. There are a couple of insecticides used for lygus control in seed alfalfa, where there is an extensive knowledge base. The first time to monitor for lygus is pre-bloom, or just as the first flowers are opening in the field. If adult lygus are present in the field, or in nearby alfalfa that is ready for harvest, a clean up spray can be applied. These are typically pyrethroids that give residual to kill bugs when they migrate into the field. If these insecticides are applied pre-bloom and allowed to dry before many flowers open, pollinators are not at high risk. Once flowers open and there are pollinators in the field, the choice of insecticides is limited. During bloom, Dibrom is often used for lygus control. This organophosphate has a very short residual. It is typically applied at night, when bees are not active. Once it dries, there is no residual activity. It is termed a "flash" kill of insects present in the field at the time of application. If dew or any free moisture is present in the field during application, bees WILL be killed when they begin foraging in the morning. It is critical that relative humidity is monitored during Dibrom applications to be sure that there is no dew formation. A new growth regulator insecticide, Rimon has been used in seed alfalfa fields since 2007. This material affects immature insects as they molt by inhibiting the synthesis of chitin. It has no effect on adult insects or other wildlife. Rimon has excellent residual and is an effective lygus control agent in seed alfalfa. It is often tank mixed with dibrom if there are many adult lygus present.

Photo Gallery
Lygus feeding on Penstemon Lygus feeding on this Penstemon speciosus caused these black tears. Seed yield was severely impacted in this field. This picture was taken by Clinton Shock.
Mouthparts on a Lygus Bug This picture shows Lygus piercing and sucking mouthparts used to feed on plants.
Lygus feeding damage Lygus damage on seed alfalfa appears as barren seed stalks. Damage appears long after bugs are gone.


Lygus management in cotton (California)

Alfalfa management for lygus control in cotton

This page was updated on April 26, 2014