An adult root weevil is between 2-3 millimeters long.
The houndstongue root weevil is present in all the counties that are green and suspected in the teal colored counties
Root weevil larvae are between 1-4 millimeters long and are found in the roots.
Feeding on the leaves by the root weevil leaves circular or oval holes.
Houndstongue is a well-known noxious weed here in the Seeley, Swan and Blackfoot region. As a member of the Borage family, it contains pyrrolizidine alkaloids that make it toxic for livestock to ingest. We often find the seeds before we find the plants themselves, as the seeds are known for their Velcro like characteristics that easily attach to our pants and pets.
Houndstongue can grow in a variety of habitats and is very successful at spreading. This noxious weed is a biannual plant, meaning that it germinates and lives as a rosette for one year and the following year it will flower, seed then die.
Houndstongue can be successfully managed with herbicides and digging. Although, there is a new to the valley biocontrol agent that is attacking the plant and has a lot of people excited!
The following is an update and description of the houndstongue root weevil (Mogulones crucifer) written by Melissa Maggio with the Montana Biocontrol Coordination Project, mmaggio@missoulaeduplace.org
Background: The houndstongue root weevil was approved for release in Canada in the late 1990s, where it has effectively suppressed houndstongue infestations. However, due to perceived risks to non-target plants, it is not currently an approved biocontrol agent in the U.S. Nevertheless, the weevil has made its way into Montana (see map). Regardless of its presence in Montana, it is illegal to aid in its movement.
Identification and Biology: To identify the weevil's presence in an area, look for adults on plants (spring and fall), larvae in roots (summer) and feeding damage on leaves (spring – fall). Adult weevils are 2-3 millimeters (mm) long and brown with a white cross on their backs. Larvae are 1-4 mm long, white with a brown head and curl in a C-shape in the roots. Feeding damage on leaves results in circular or oval holes.
Biology: In spring adult weevils emerge from the soil where they overwinter. From spring to early summer, weevils feed on houndstongue leaves, mate and lay eggs at the base of the leaves. The larvae inflict the most significant damage by feeding on the roots. This feeding damage can result in plant death, prevention of flowering or a reduction in seed production. Larvae emerge from the roots to complete their life cycle in the soil. New adults emerge in late summer and early fall to feed on houndstongue foliage before overwintering in the soil.
Impacts: This weevil has been very effective at reducing houndstongue infestations in Canada and in the portions of the U.S. where it has naturally migrated. At sites where the weevil has been present for multiple years, houndstongue is rare or absent. Feeding on native plants in the same family as houndstongue has been documented in both Canada and the U.S., but to date this non-target attack seems minor, sporadic and temporary. The biggest concern is its potential impact to federally listed plant species.
Current Status: While the weevil is not currently approved as a biocontrol agent in the U.S., there is ongoing research to help inform the regulatory approval process. Research includes chemical ecology, continued lab and field cage tests. A monitoring project occurring in Montana, Washington and Idaho looking for impacts to plant species other than houndstongue in areas that the weevil has moved into naturally. Until approved, this weevil will continue to be considered an agricultural pest and, as such, cannot be intentionally moved.
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