|Biological agent type
Seed head weevil
Plant species attacked
yellow starthistle (Centaurea solstitialis)
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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
Mode of attack
The adults feed on the young developing buds, causing the buds to die, causing a characteristic grayish-white hook. Adults have been found to feed on the seed heads of other knapweeds that grow in proximity to yellow starthistle.
Adult and larvae stage.
Collection and release information
Widespread in distribution, can be collected by sweep net June-July. Consult with ODA for availability for your area.
History in Oregon
The seed head weevil Eustenopus villosus was released in Douglas County in 1990 and 1991. It was recovered in 1991. The Myrtle Creek site, in Douglas County, served as the main nursery site for collection. The weevil can drastically reduce flower and seed production of the plant. In 1996 collections at the Myrtle Creek site were difficult because of the low density of yellow starthistle. Reduced grazing and increased plant competition in combination with the biocontrol agents contributed to the decline.
Release status in Oregon
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