Biological agent type
beetle-root borer
Plant species attacked
diffuse knapweed (Centaurea diffusa)
spotted knapweed (Centaurea stoebe)
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Images by Eric Coombs, Oregon Department of Agriculture.
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If images are downloaded and used from the ODA web site please be sure to credit the photographer.
Site of attack
Center of the root.
Mode of attack
Larvae feed in the roots causing galls and stressing the plant.
Destructive stage
Larval-internal.
Collection and release information
This beetle is widespread and adults can be collected with sweep net June-July. Consult with ODA for availability for your area.
History in Oregon
The root-boring beetle Sphenoptera jugoslavica was introduced in 1980 in Wasco County. It is now widely distributed and often infests over 95% of the rosettes. Some reductions in plant density have been observed, especially in Wasco and Morrow Counties, where it occurs with Larinus minutus. It is also being used against spotted knapweed.
Release status in Oregon
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