Native Plants Seed Production

Western Colorado Entomology
Pests Affecting Native Plant Seed Production

Scientific Name: Hedysarum boreale Nutt.

Common Name: Utah Sweetvetch, Northern Sweetvetch

Plant Abbreviation:

Description: Utah sweet vetch is a nitrogen fixing legume that grows on western rangelands. There is significant seed production in CO, UT and ID. 'Timp' is a released variety and several ecotypes are in production. A widespread seed weevil, Acanthoscelides sp. has reduced yield by 75% in extreme situations. Lygus bugs can reduce seed set. The larvae of several native butterflies and moths can feed on foliage and seed pods, although we have not yet seen significant damage from them. Sweetvetch production is also impacted by a rust disease and root rot disease which are poorly understood.

Hedysarum Seed Beetle

Scientific Name: Coleoptera: Bruchidae: Acanthoscelides sp. The Hedysarum seed beetle is widespread across the west. It is recorded in HEBO seed production plots in CO, UT and ID. Losses of 75% were recorded in the early 1990's in a field at Meeker, CO. The beetle was originally identified as A. fraterculus (1) , but recent taxonomy work has shown that it is probably an undescribed species. A. fraterculus is recorded from several species of legumes but it is possible that the undescribed species has a more limited host range. (1) Johnson, C.D. 1990. Confirmation of Hedysarum boreale Nuttall (Leguminosae) as a host plant for Acanthoscelides fraterculus (Horn) (Coleoptera: Bruchidae). Pan-Pac. Entomol. 66 (2): 175-176
Adult	Adult beetles are about 1.5 mm in length and brown in color. Their snout is broad,. Males appear in the field shortly before the first flowers bloom, and females are present at first bloom. Beetles are easily found using a sweep net, but are not readily apparent with simple visual searches.
Egg	Eggs have not been described. They are laid either in or on developing seed pods.
Larva	Larvae spend most of their life within infested seeds. The seed in the upper picture was damaged when a larva chewed its way out. Larvae are small (about 2 mm long when fully grown), yellowish grubs with no legs and a small head capsule (middle picture). The mouth parts are exposed and constitute most of the brownish area at the tip of the head. Larvae feed within the seed pods on developing seed, destroying it. The seed pod pictured in the bottom picture had a beetle larva feeding within. The hole was created as the larva exited the seed.
Pupa	Pupation is probably in the soil but we have not yet seen a pupa in the field.

Management

It is important to monitor HEBO seed fields at first bloom for seed beetles. A sweep net is an excellent, inexpensive, monitoring tool. We have treated fields that have one or two seed beetles per ten sweeps. There are no good thresholds set, but if beetles are easily found and you wish to maximize production, an insecticide application may be used. Bees will be visiting the field when flowers appear so it is important to time a spray as soon as possible before bloom appears. Pyrethroid insecticides work very well against adult beetles. If flowers are present in the field, spray at night, when they have time to dry before bees become active in the morning. Allowing the spray to dry before bees become active will minimize bee kill.

Keep monitoring seed beetle activity during bloom. If beetles appear during bloom, a night time application of a non residual insecticide may work to reduce the beetle numbers while protecting bees.

Photo Gallery

	Utah sweetvetch production in Colorado.
	Sweep net sampling of a field of Utah sweetvetch.
	Sweetvetch production at Western Colorado Research Center at Rogers Mesa. This field is being grown for the Uncompahgre Project.

Links

For more information visit the USDA Natural Resources Conservation Service Plant Database