|Pests Affecting Native Plant Seed Production|
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.
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.
This page was updated on March 8, 2011