|Biological agent type
seed head weevil
Plant species attacked
diffuse knapweed (Centaurea diffusa)
spotted knapweed (Centaurea stoebe)
meadow knapweed (Centaurea pratensis)
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Images by Eric Coombs, Oregon Department of Agriculture.
If images are downloaded and used from the ODA web site please be sure to credit the photographer.
Site of attack
Larvae feed on the developing seeds, and adults can cause severe defoliation during population outbreaks.
Mode of attack
The larvae feed in the flower receptacle destroying most of the seeds. Heavy attack by adults can stunt or kill plants, delay flowering, and are causing spectacular stand density reductions at numerous sites in eastern Oregon. Extensively defoliated plants may recover and produce multi-stemmed plants when sufficient rain occurs.
Larval and adult.
Collection and release information
Widespread in distribution and can be collected by sweep net June-July. Consult with ODA for availability for your area.
History in Oregon
The seed head weevil Larinus minutus was released in Morrow County in 1992. The weevil is now widespread and abundant at most infestations in Eastern Oregon. Attack rates at many sites exceed 95% of the seed heads. This insect also does well on spotted knapweed and was recently recovered on meadow knapweed.
Release status in Oregon
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