Description and life history
Prionus beetles belong to the family Cerambycidae, commonly called long-horned beetles because of their very long antennae. The California prionus is widely distributed in the Pacific Northwest, and has been recorded as a pest of hops in Idaho for over 60 years.

Adults are large brown beetles that emerge from overwintering sites in the soil from early June until early August to mate and lay eggs. Female prionus appear to be sedentary and may emit a pheromone to attract potential mates. Oviposition behavior is not well understood but eggs are laid in the soil from ½ to 1½ inches below the surface. A single female prionus can lay 150 to 200 eggs during her 30 to 60 day life. Larvae emerge from eggs and begin feeding on plant roots.

Larvae are cream to brown in color and grow from less than ½ to about 3 inches in length over a three to four-year period. Larvae can be found in roots from 2 to 8 inches below the soil surface. Smaller larvae (less than ½ inch) are found deeper in the root zone than larger larvae, and tend to tunnel in roots. Larger larvae tend to graze and prune larger roots closer to the soil surface. Mature larvae pupate in cells constructed from soil and lined with root material. (back to top)

Damage to hop
Adult prionus are not known to damage hop plants. However, larvae feeding on the roots of hop plants can cause economic loss. Root feeding by prionus larvae damages plant roots resulting in decreased nutrient uptake, water stress and reduced plant growth. Severe infestations can completely destroy plant crowns resulting in plant death. Less severe infestations can result in the wilting, yellowing and death of one or more bines of infested plants. (back to top)

California Prionus Management
Management of prionus in hop consists of identifying and removing infested plants. Occasionally, it may be necessary to dig up and remove all plants in severely infested fields. Once the infested plants have been removed, the field can be fumigated, or planted to a non-host crop for 2-3 years to reduce prionus populations before replanting the field to hop. However, larvae can survive for extended periods by feeding on dead woody tissue, such as trellis support poles found in hop fields. There are no hop varieties or accessions identified as being resistant to California prionus. No economically significant natural enemies have been identified. A pheromone may be involved in prionus mating behavior. Prionus management using mating disruption or adult trapping techniques may be possible if the existence of a mating pheromone can be confirmed, and the compound(s) isolated. There are no chemicals presently registered for control of prionus in hop.